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Reduced Herbicide Inputs for Weed Management in Florida Peanut (Arachis hypogaea L.) Production


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REDUCED HERBICIDE INPUTS FOR WEED MANAGEMENT IN FLORIDA PEANUT ( Arachis hypogaea L.) PRODUCTION By SAMUEL D. WILLINGHAM A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004

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ACKNOWLEDGMENTS For their support and guidance at the University of Florida, I wish to express sincere appreciation to my graduate committee: Dr. Barry Brecke, Dr. Greg MacDonald, Dr. Joyce Tredaway Ducar, and Dr. Ben Whitty. I would like to acknowledge Nick Pool, Melissa Barron, Amanda Collins, and Nasir Shaik. While their assistance helped make this research possible, their fellowship and camaraderie also made my time at the University of Florida enjoyable. ii

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iii TABLE OF CONTENTS page ACKNOWLEDGMENTS..................................................................................................ii LIST OF TABLES...............................................................................................................v ABSTRACT......................................................................................................................v ii CHAPTER 1 INTRODUCTION........................................................................................................1 Current Management Strategies...................................................................................2 Diclosulam, Flumioxazin, and Imazapic......................................................................4 Reduced Rate Herbicide Research................................................................................6 Row Spacing Research.................................................................................................7 New Peanut Varieties.................................................................................................10 Summary.....................................................................................................................14 2 EFFECTS OF REDUCED APPLICATIONS OF DICLOSULAM, FLUMIOXAZIN, AND IMAZAPIC ON WEED MANAGEMENT IN PEANUT ( Arachis hypogaea L.) PRODUCTION.....................................................................................................16 Introduction.................................................................................................................16 Materials and Methods...............................................................................................18 Results and Discussion...............................................................................................21 Weed Control-2002.............................................................................................21 Weed Control-2003.............................................................................................22 Peanut Yield........................................................................................................24 Economic Analysis..............................................................................................25 3 EFFECTS OF REDUCED COST HERBI CIDE TREATMENT COMBINATIONS ON WEED MANAGEMENT IN PEANUT ( Arachis hypogaea L.) PRODUCTION...........................................................................................................49 Introduction.................................................................................................................49 Materials and Methods...............................................................................................51 Results and Discussion...............................................................................................53 Weed Control-2002.............................................................................................53 Weed Control-2003.............................................................................................54

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Peanut Yield........................................................................................................55 Economic Analysis..............................................................................................57 4 PEANUT (Arachis hypogaea L.) VARIETY RESPONSE TO SELECTED HERBICIDES.............................................................................................................73 Introduction.................................................................................................................73 Materials and Methods...............................................................................................74 Results and Discussion...............................................................................................76 Peanut Injury.......................................................................................................76 Canopy.................................................................................................................78 Peanut Yield........................................................................................................79 5 SUMMARY AND CONCLUSIONS.........................................................................89 APPENDIX DAILY PRECIPITATION............................................................................94 REFERENCES..................................................................................................................98 BIOGRAPHICAL SKETCH...........................................................................................102 iv

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LIST OF TABLES Table page 2.1 2002 Reduced rate treatments-Jay and Citra, FL...................................................27 2.2 2002 Reduced rate treatmentsMarianna, FL........................................................28 2.3 2003 Reduced rate treatmentsJay and Citra, FL..................................................29 2.4 Weed control as affected by reduced rate herbicide treatments in 2002 at Jay, FL...................................................................................................................31 2.5 Weed control as affected by reduced rate herbicide treatments in 2002 at Citra, FL.................................................................................................................32 2.6 Weed control as affected by reduced rate herbicide treatments in 2002 at Marianna, FL..........................................................................................................33 2.7 Weed control as affected by reduced rate herbicide treatments in 2003 at Citra, FL in single row study.................................................................................34 2.8 Weed control as affected by reduced rate herbicide treatments in 2003 at Citra, FL in twin row study....................................................................................36 2.9 Weed control as affected by reduced rate herbicide treatments in 2003 at Jay, FL in single row study....................................................................................38 2.10 Weed control as affected by reduced rate herbicide treatments in 2003 at Jay, FL in twin row study......................................................................................40 2.11 Peanut yield as affected by reduced herbicide treatments in 2002 at Jay and Citra, FL.................................................................................................................42 2.12 Peanut yield as affected by reduced herbicide treatments in 2002 at Marianna, FL...........................................................................................................................43 2.13 Peanut yield as affected by reduced rate herbicide treatments in 2003 at Jay and Citra, Fl. in twin and single row studies..........................................................44 2.14 Total revenue per treatment as affected by yield and treatment cost separated by location and row spacing........................................................................46 v

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2.15 Herbicide treatment cost for reduced rate study..........................................48 3.1 2002 Reduced Cost Herbicide Treatments............................................................59 3.2 2003 Reduce Cost Herbicide Treatments..............................................................61 3.3 Weed control with reduced cost herbicide treatments in 2002 at Jay, FL.............63 3.4 Weed control with reduced cost herbicide treatments in 2003 at Jay, FL.............64 3.5 Weed control with reduced cost herbicide treatments in 2003 at Citra, FL..........65 3.6 Weed control with reduced cost herbicide treatments in 2003 at Marianna, FL...66 3.7 Yield with reduced cost herbicide treatments in 2002 at Jay, FL..........................67 3.8 Yield with reduced cost herbicide treatments in 2003 at Jay, Citra, and Marianna, FL..........................................................................................................68 3.9 Herbicide treatment cost for reduced cost study-2002..........................................69 3.10 Herbicide treatment cost for reduced cost study-2003..........................................70 3.11 Total revenue for reduced cost treatments at Jay, FL..................................71 3.12 Total revenue for reduced cost treatments...................................................72 4.1 Variety tolerance herbicide treatments, Jay and Citra, FL. 2003...........................82 4.2 Percent injury as affected by treatments compared to non treated check for each variety at each measurement interval pooled over locations.........................83 4.3 Canopy means for each treatment averaged over all varieties at Jay and Citra, FL...........................................................................................................................84 4.4 Canopy means for each variety averaged over treatments at Citra, Fl..................85 4.5 Yield of each variety averaged over all treatments at Jay, FL..............................86 4.6 Yield as affected by treatments averaged over all varieties at Jay, FL..................87 4.7 Yield of each variety per treatment with significance compared to the non-treated control (check)....................................................................................88 A.1 Daily precipitation (cm) for Citra, FL. May 2002 September 2002....................95 A.2 Daily precipitation (cm) for Jay, FL. May 2002 September 2002......................96 A.3 Daily precipitation (cm) for Jay, FL. May 2003 September 2003......................97 vi

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science REDUCED HERBICIDE INPUTS FOR WEED MANAGEMENT IN FLORIDA PEANUT (Arachis hypogaea L.) PRODUCTION By Samuel D. Willingham May 2004 Chair: Barry J. Brecke Cochair: Greg MacDonald Major Department: Agronomy Field studies were conducted in 2002 and 2003 at Citra, Jay, and Marianna, FL, to evaluate the effects of reduced herbicide inputs on weed management and yield in peanut in both twin-and single-row spacing regimes. Economic return was also calculated to determine the return to management for all herbicide systems. Seven peanut varieties recently released by the University of Florida in 2002 were evaluated to determine tolerance to five commonly used herbicide systems. At Jay and Citra in 2002, diclosulam plus flumioxazin applied preemeregence (PRE) at 1/4x (1/4 labeled use rate) followed by imazapic post emergence (POST)at or 2/3x was the lowest herbicide input that provided greater than 85% control of common cocklebur (Xanthium strumaruim L.), sicklepod (Senna obtusifolia L.), and yellow nutsedge (Cyperus esculentus L.) and greater than 90% control of pigweed (Amaranthus spp), hairy indigo (Indigofera hirsuta L.), and Florida beggarweed (Desmodium tortuosum sw. DC). vii

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At Citra in 2003, the twin row pattern provided greater overall control of tropcal spiderwort (Commelina banghalensis L.) than the single row pattern (75 and 65%, respectively). Diclosulam applied with flumioxazin PRE followed by (fb) imazapic POST both at x for twin and at 1/2x for single rows was the lowest input that provided greater than 82% control. Sicklepod required 1x treatments for > 85% control and Florida beggarweed control was > 85% except with diclosulam alone or fb imaxapic at 1/4x. Diclosulam controlled purple nutsedge 10 to 20% greater than flumioxazin. Total revenue at Citra and Jay was highest for diclosulam applied with flumioxazin followed by imazapic, all at 1/2x ($1981.68 and $986.00/ha, respectively). In the reduced cost studies at Jay in 2002 and 2003, and at Citra and Marianna in 2003, the greatest level of weed management was observed with pendimethalin pre plant incorporated (PPI), fb imazapic and/or 2,4-DB POST. At Marianna, treatments with pendimethalin PPI alone or fb diclosulam PRE fb imazapic 1/2x and/or mixed with 2,4-DB POST were the highest yielding at 4374, 4511, and 4394 kg/ha, respectively, resulting in the highest total revenue. C-99R and Hull displayed the greatest injury late-season from paraquat at-cracking (AC) fb chlorimuron at 2x. All varieties exhibited 25-35% injury from paraquat AC 1x alone. Varieties exhibited < 21% injury from diclosulam PRE. Flumioxazin PRE injured UF00324 (75%) and Norden (71%), and imazapic injury was highest for AP-3 (38%) and Hull (33%). All varieties recovered by late season. At Citra, DP-1 and Hull consistently had smaller canopy over all treatments. Paraquat AC fb imazapic EPOST significantly reduced canopy size for all varieties. Variety AP-3 was the lowest yielding and significantly lower than Carver while DP-1 was the highest yielding vii

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when averaged across all treatments at Jay. At Citra, DP-1 was the only variety where yield for all four herbicide treatments were significantly lower than the non-treated. vii

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CHAPTER 1 INTRODUCTION In 2002, approximately 3.19 million hectares of peanut (Arachis hypogaea L.) were harvested in the United States with an average yield of 2,870 kg/ha (United States Department of Agriculture 2002). This was a 5% reduction from 2001 and a 4% reduction from 2000. Growers in the Southwest (New Mexico, Oklahoma, and Texas) planted 180,000 hectares of peanut in 2001, 16% less than 2000. Plantings in the Virgina-North Carolina region totaled 67,000 hectares a 17% reduction from 2001. These changes in peanut production were most likely the result of change in farm subsidize programs that resulted in a less favorable pricing structure than was available under previous legislation. The Southeast (Alabama, Florida, Georgia, and South Carolina) is the largest peanut production region in the United States with over 350,000 hectares planted in 2002, an increase of 6% from 2001 (USDA 2002). Florida is ranked 5th nationally in peanut production with Jackson County being the 3rd leading peanut producing county in the United States. In 2002, Florida growers harvested 35,000 hectares with an average yield of 2,600 kg/ha (Aerts and Nesheim 2000). States with the highest average yield in 2002 were Texas: 3,500 kg/ha, New Mexico: 3,400 kg/ha, Oklahoma: 3,100 kg/ha, Georgia: 2,900 kg/ha, and Florida: 2,600 kg/ha (USDA 2002). Since 1990, the price per kilogram received for peanut has declined considerably from $0.66/kg to the current price of less than $0.40/kg. The 2002 Farm Bill is an important factor in determining profit potential of peanuts. Farmers were receiving 1

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2 $0.67/kg quota price but that changed with the 2002 Farm Bill to $0.39/kg. According to Dr. Nathan Smith from the University of Georgia, the variable cost for peanut production will be lower for 2003 averaging $0.29/kg for non-irrigated and $0.33/kg for irrigated compared to $0.42 for non-irrigated and $0.52 for irrigated in 2002. The factor having the most significant impact on variable cost will be the price of seed and seed price has declined as a result of the lower price paid for peanut (Smith 2003). Current Management Strategies Pest management accounts for a large portion of the variable production costs for peanut. More than 36% of the total operating costs are invested in pesticides. In peanut, there are over 43 weed species, 20 insect pests, 17 disease and 4 nematode pathogens that are of economic importance in 9 peanut producing states. The worst weed pests, if left uncontrolled, can reduce yield 30-80 percent in infested areas (Aerts and Nesheim 2000). The most troublesome weeds in Florida peanut fields in 2001 were 1) Florida beggarweed (Desmodium tortuosum L.) 2) sicklepod (Senna obtusifolia L.) and 3) nutsedge spp. (Cyperus spp.) (Webster 2001). Peanut yields were reduced 15.8 to 30.2 kg/ha by Florida beggarweed and 6.1 to 22.3 kg/ha by sicklepod for each weed per 10 m2 (Hauser et al. 1982). Peanut weed control is accomplished through cultural, mechanical, and chemical methods. Crop rotation has many benefits and one of these is the better weed control that can be a benefit to crop rotations most likely the benefit is to rotate herbicides. Continuous use of a single mode-of-action herbicide can lead to development of resistance where weed biotypes that were once controlled are no longer affected by that herbicide.

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3 Adoption of reduced tillage cropping practices that rely on in-crop selective herbicides has lead to widespread change of rigid ryegrass (Lolium rigidum Gaud.) and wild radish (Raphanus raphanistrum L.) populations in Western Australia with resistance to acetolactate synthase (ALS)-inhibiting herbicides (Walsh et al. 2004). ALS herbicides were introduced in 1982 and due to continuous use, resistance was first reported in 1987 (Walsh et al. 2001). By 1999, ALS-herbicide resistance had developed in 83 weed species worldwide (Heap 2000). Mixing herbicides with different modes of action reduces the probability of weed resistance and weed shifts. Cultivation may also be utilized to slow the onset of weed resistance. In peanut, the most effective weed control and highest yields have generally been obtained using a herbicide program consisting of a preplant incorporated (PPI) or preemergence (PRE) treatment followed by an at cracking (AC) stage treatment when the plant is just emerging through the soil surface followed by a postemergence (POST) application (Ducar et al. 2002). Traditional herbicide applications have included pendimethalin or ethalfluralin PPI for control of annual grasses and small seeded broadleaf weeds followed by a PRE application of diclosulam, flumioxazin, metolachlor, or norflurazon for additional control of broadleaf weeds. At cracking and POST herbicides most commonly used in Florida peanut production include paraquat for broad spectrum early season weed control; bentazon for control of yellow nutsedge (Cyperus esculentus L.) and various broadleaf weeds; 2,4-DB for control of morningglory spp. (Ipomoea spp.) and sicklepod (Senna obtusifolia L.); chlorimuron or imazapic for late season Florida beggarweed (Desmodium tortuosum sw. DC), nutsedge, and multiple broadleaf weed species control (Ducar et al. 2002).

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4 Traditional herbicide practices require that the herbicides previously mentioned be applied at the full labeled rate. With the reduction of revenue due to the new Farm Bill, farmers will need new tactics to reduce their production cost possibly by configuring herbicide treatment combinations that will reduce the cost of weed management. Diclosulam, Flumioxazin, and Imazapic Over the past 6 years, three herbicides (diclosulam, flumioxazin, and imazapic) have been introduced for broad-spectrum weed control in peanut production. Two of these herbicides (diclosulam and imazapic) have a similar mode-of-action. Either of these can be tank mixed with the third (flumioxazin) to get broad-spectrum weed control while reducing the likelihood of developing weed resistance. Diclosulam, [N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimidine-2-sulfonamide], is a new triazolopyrimidine sulfonanilide herbicide from Dow AgroSciences registered in peanut. It received Section 3 label in 2000 for use in peanut as a soil applied herbicide for broadleaf weed control. Diclosulam can be applied PPI, preplant surface, or PRE through true AC at the maximum rate of 27 g ai/ha. Rotational restrictions for various crops do exist for this herbicide. There is a 10 month restriction for cotton and an 18 month restriction for corn, however, some research indicates these restrictions may not be necessary. Cotton, corn and sorghum planted the year following diclosulam applied at up to three times the labeled rate showed no difference in fresh or dry weights of any crop (Gerngross and Senseman 2002). Diclosulam is absorbed through the roots and shoots of germinating seedlings as they grow and expand through the soil. Exposure to diclosulam prevents sensitive weed seedlings from emerging, or if they do emerge they do not develop beyond the cotyledon stage. Diclosulam inhibits the acetolactate synthase (ALS) enzyme that is involved in the

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5 synthesis of branched chain amino acids (isoleucine, leucine, and valine) that are required for plant growth (Vencill 2002). Flumioxazin, (2-[7-fluoro-3,4-dihydro-3-oxo-4-(2-propynyl)-2H-1,4-benzoxazin-6-yl]-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione), is a new herbicide developed by Valent USA Corp. for broadleaf weed control in cotton (Gossypium spp.), peanut, sugarcane (Saccharum officinarum L.), and soybean (Glycine max L.). Flumioxazin is a N-phenylpthalimide derivative, which is new chemistry for peanut, cotton, and sugarcane. The mode of action of this family is inhibition of the protoporphyrinogen oxidase (PPO) causing peroxidation of membrane lipids, which leads to damage of membrane functions. Flumioxazin may be applied to peanut prior to planting as a preplant burndown or PRE at 70 to105g ai/ha depending on the weed species and/or the weed density (Cranmer et al. 2000). Preemergence applications must be made within 2 days after planting. Applications after peanut have begun to crack or emerge result in severe crop injury. Rotational restrictions do exist for flumioxazin, however, the rotational interval is shorter compared to other herbicides. Cotton, field corn, rice, sorghum, tobacco, wheat, and sugarcane may be planted 30 days after application for the 70g ai/ha rate and 2 months for the higher rate (Valor 2001). Imazapic, [(+,-,)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid], is an imidazolinone herbicide produced by BASF and was labeled for use in peanut in 1996. It is applied to approximately 75 % of Florida's peanut hectarage at a rate of 70g ai/ha early POST. Imazapic controls various

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6 broadleaf weeds, grasses, yellow and purple nutsedge and can be applied over the top of peanut without causing crop damage. Similar to diclosulam, imazapic inhibits acetolactate synthase (ALS), a key enzyme in biosynthesis of the branch-chain amino acids (Vencill 2002). Compared to the previously described herbicide, imazapic has very strict rotational restrictions. Nine months must pass after imazapic application before planting field corn, soybean, tobacco, snap, and southern pea. There is an 18 month interval between imazapic application and planting of cotton, grain sorghum, sweet corn, and oats (Cadre 2001). Significant cotton damage has been observed when it was planted the season following imazapic application to peanut. In one study, cotton injury was greater than 50% 2 wk after planting (WAP) when 9 to 36 g ai/ha was applied and greater than 60% injury at 6 WAP (Dotray et al. 2002). Reduced Rate Herbicide Research Peanut is a high management, high input crop with the cost of inputs steadily increasing. Overall, yields have not increased for several years, even with new varieties and technological advances. To remain competitive in a global market, farmers must find ways to improve production efficiency or increase yields (Wright et al. 2001). Reducing the amount of herbicides applied can help reduce the 36% of production cost due to pesticide applications. Research has been conducted using the full labeled rates of imazapic, diclosulam and flumioxazin alone and in mixtures to examine weed control, peanut tolerance, and yield. Weed control has been successful at these rates. Research has also been conducted using these same three herbicides but at reduced rates in peanut in an attempt

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7 to maintain weed control while reducing cost and to reduce the potential for imazapic carryover. Previous research indicates that imazapic, diclosulam, and flumioxazin can be applied at reduced rates and still provide adequate weed control. Swann conducted a study in 2000 that evaluated diclosulam applied PRE at 8.8 (.33X), 17.7 (.66X), and 26.5 (1X) g ai/ha to peanuts. Yellow nutsedge (Cyperus esculentus L.) control was greater than 83% and control of common ragweed (Ambrosia artemisiifolia L.) was greater than 78%. When reduced rates of diclosulam were followed by imazapic applied early POST, also at reduced rates, yellow nutsedge control increased to 88% and common ragweed control increased to 99% (Swann 2000). Troxler et al. (2001) conducted a study with diclosulam applied at 13g/ha (.5X) and flumioxazin applied at 52 g ai/ha (.5X). He concluded that weed control was comparable to the 1X rates for the two herbicides for all weeds evaluated. When diclosulam and flumioxazin applied at .5X were followed by imazapic applied at 35g/ha (.5X) it was concluded that these rates provided similar weed control to the regional standard. In Northwest Texas at one location, yellow nutsedge control was 85% or greater with imazapic applied at the 1/2X rate in combination diclosulam at the 1/2X rate. At the second location, yellow nutsedge control was less than 70%. In South Texas, imazapic applied alone at the 1/2X rate or used in combination with diclosulam at 1/2X rate controlled Palmer amaranth (Amaranthus palmeri S.), smellmellon (Cucumis melo L), and yellow nutsedge 80% or greater (Baughman et al. 2003). Row Spacing Research Improving production efficiency and yield is essential for peanut producers to remain competitive. Closer spacing of rows is one way to improve yield that has been

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8 studied since the early 1900's but has not been adopted by farmers until recently. Parham (1942) reported that Spanish peanut yields were higher in 46 cm rows than in 61, 76, 91, and 107 cm rows. Due to cultivation requirements he suggested a spacing of 67 to 76 cm as the most practical. More recent studies indicate that planting peanut in a twin row spacing pattern increases yields, decreases incidents of Tomato Spotted Wilt Virus (TSWV), and may increase grade by 1 to 2% compared to traditional single row patterns. TSWV affects peanut by decreasing yield and decreasing sound mature kernel percentage (TSMK) (Baldwin et al. 1998). In a twin-row system, peanut row centers remain 91 centimeters apart with the seeds planted in rows on each side of the 91 cm center with the twin rows spaced 19 to 23 cm apart. The seeding rate per hectare is the same for twin-row spacing with three seed per 30.5 cm for each row versus conventional row spacing with six seed per 30.5 cm for one row. Twin-row planting scheme results in quicker canopy coverage (as much as two weeks earlier) which helps in weed control and higher grades due to a greater taproot crop and less of a limb crop (Wright et al. 2001). Wehtje et al. (1984) studied the effect of twin-row spacing on 'Florunner' production and reduced herbicide applications. The results showed that yields improved in twin rows only when weed competition was reduced to a minimum and that, consequently, weed control inputs could not realistically be reduced. In 1985, Colvin et al. studied the effects of row patterns and weed management systems on weed control, peanut yield, and net return. Broadleaf fresh weights were significantly lower for the dual pattern in 1981 and grass fresh weight significantly lower in 1983. Peanut yields

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9 were higher for the dual pattern in 1981 and 1983 and equal to the standard in 1982. The average net returns were higher for the dual pattern when compared to conventional. In 1986, Cardina et al. studied weed control using reduced rates of standard herbicides on 'Sunbelt runner' planted in twin-row patterns. A 30-60% reduction in residual herbicide rates resulted in weed control and crop yield equivalent to the standard treatment. He concluded that there was potential for reducing herbicide inputs in twin-row peanut without sacrificing yield or quality (Cardina et al. 1986). Sicklepod density in plots treated with dimethenamid-P alone was approximately 2/m2 in 2001 and 40/m2 in 2002. Sicklepod control was 9 and 11% higher in twin rows compared with single rows when evaluated late in the growing season (Lanier et al. 2003). This data suggest that seeding peanut in twin rows improve weed control when compared with seeding in single rows. A field study was conducted by in Texas evaluated the impact of reduced and full rates of imazapic and diclosulam when applied to peanut in twin row and conventional planting configurations. Averaged across all treatments yellow nutsedge control was significantly better in the twin row spacing (87%) compared to conventional row spacing (70%) (Besler et al. 2002). Yield increases of 565 and 426 kg/ha were observed with 'Florunner' and 'Southern Runner', respectively, when grown in twin rows compared to single rows in 1992 (Beasley et al. 1992). In twin rows, the 3 seeds per 30.5 centimeters of Georgia Green cultivar resulted in significantly higher yields (4625 vs. 4301 kg/ha) and less TSWV (12% vs. 18%) when compared to 2 seeds per 30.5 centimeters. Net returns for two,

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10 three, or four seeds per 30.5 centimeters of row were $328, $437, and $264/ha respectively (Baldwin et al. 2000). When four different peanut cultivars ('Georgia Green', 'ViruGard', 'SunOleic 97R', and 'Flavor Runner 458') were planted in twin rows versus single rows the results were similar to previous research. When averaged across cultivars and locations, the twin row pattern resulted in significantly higher yield and total sound mature kernel (TSMK) and significantly reduced other kernel (OK) and TSWV incidence (Baldwin et al. 1998). The response of another cultivar (VA 98R) to twin row planting versus single row planting resulted in yield increases ranging from 264 to 703 kg/ha and were obtained in four on-farm tests. The increase in value averaged $341/ha (Mozingo and Swann 2000). In 2001, a new Tomato Spotted Wilt Virus resistant peanut cultivar was released, tested in a twin row pattern, and compared to a single row pattern. The results indicated less TSWV in the twin row pattern compared to the single row (19.8% versus 6.9%) (Baldwin et al. 2001). Less TSWV is the main reason for renewed interest in twin rows because TSWV incidence has been increasing in the southeast since 1986. Research since that time has shown that in the presence of TSWV there is a positive effect on yield when seeding rates are high enough to establish a final stand count of at least four plants per foot of row. Increasing seedling count, while guaranteeing a uniform stand, also increases production costs. New Peanut Varieties Differential response to herbicides is common in peanut (Jordan et al. 1998). 'Early Bunch', a Virginia market type peanut, exhibited early-season injury from naptalam plus dinoseb and paraquat applied early post emergence (Brecke 1989). Imazapic reduced percentage of extra large and jumbo kernels in 'Florunner' and 'Sunrunner" cultivars.

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11 Imazapic injury was also reported with 'Florunner', 'Georgia Runner', 'GK 7', 'NC 7', 'NC-V11', 'Southern Runner', 'Sunrunner', and 'Agra Tech VC-1' cultivars (Richburg et al. 1995). Research in Texas has shown diclosulam applied PRE at 18 and 27 g ai/ha injured 'Flavor Runner 458', 'Sunoleic 97R', 'TX 977006', and 'Georgia Hi O/L' varieties 10 to 40% 14 DAT but did not injure 'Tamrun 96'. Injury remained 20 to 25% 42 DAT for the 'Flavor Runner 458' and 'Sunoleic 97R' varieties and 35 to 45% for the 'Georgia Hi O/L' from diclosulam applied PRE at 27 g ai/ha (Murphree et al. 2003). In 2000, diclosulam applied PPI at 18, 27, or 54g ai/ha to three runner market-type peanut cultivars, 'Georgia Green', 'C-99R', and 'MDR 98', in Florida, resulted in no peanut injury and canopy diameter was unaffected at any rate (Main et al. 2002). In much of the Southwestern production area during 2000, diclosulam caused stunting, stand loss, and chlorosis to the peanut canopy when applied PPI and PRE. Therefore, a supplemental label was issued in 2001 for Texas, New Mexico, and Oklahoma changing PRE application timing to no less than five days after planting through at-cracking at 26.8g ai/ha. In addition, Oklahoma can apply diclosulam preemergence immediately after planting through at-cracking only at 20.1g ai/ha (Strongarm 2001). Peanut injury from flumioxazin has been inconsistant. Early-season injury has been a minor concern with flumioxazin. Less than 5% injury 14 DAT was observed on all varieties from flumioxazin applied PRE at 105g ai/ha (Murphree et al. 2002). In North Carolina, early season peanut injury at 3 WAP was minimal (3% or less) in 1996 on seven Virginia-type peanut cultivars (NC 7, NC 12C, NC 9, NC 10C, NC-V 11, VAC 92R, AT VC 1) when flumioxazin was applied at 71 g ai/ha PRE.

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12 In 1997, all peanut cultivars treated with flumioxazin PRE were injured 15 to 28% at 3 WAP (Wilcut et al. 2001). This may have been due to the cold wet conditions during the 2 wk after PRE treatment. In 2002, Main et al. observed similar results with runner-type varieties. Up to 25% injury was observed from flumioxazin at 14 and 28 DAT. Flumioxazin was registered in 2001 and during its first year, injury was reported in Oklahoma, Georgia, North Carolina, and West Texas (Murphree et al. 2003). These results indicate the importance of evaluating cultivars for tolerance to current herbicide application practices. In 2003, seven new peanut cultivars developed by Dr. D. W. Gorbet at the University of Florida were released. These varieties have not been tested for their tolerance to commonly used herbicides in peanut production ('Carver', 'ANorden', 'GP-1', 'DP-1', 'Hull', 'AP-3', and 'UF00324'). 'ANorden' is a medium maturity (135-140 days) variety, with runner growth habit (prominent center stem), runner size pods and seeds, very good TSWV resistance, and with high oleic oil chemistry. It is a replacement for 'SunOleic 97R' in the Florida Foundation Seed Producers program. 'ANorden' has shown pod yields equal to or better than 'Georgia Green' in Florida tests and likewise for TSWV resistance, with somewhat larger seed size. 'ANorden' has been equal to 'Georgia Green' in resistance to white mold, leaf spot, and rhizoctonia disease. 'DP-1' is a late maturity (150+ days) cultivar with excellent disease resistance. It has the highest level of resistance to late leaf spot, TSWV, and white mold currently available in a US peanut cultivar. Yield in excess of 5000 kg/ha has been recorded in

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13 Florida tests without fungicide applied for leaf spot control. 'DP-1' has "normal" oil chemistry and seed size similar to 'GK 7'. It has somewhat less vine growth than 'C-99R'. 'Carver' is a medium maturity (135-140 days), runner growth habit, runner pod, and seed size. It has TSWV and white mold resistance that is somewhat better than 'Georgia Green' with some resistance to CBR, Rhizoctonia limb rot and late leaf spot. 'Carver' has excellent yield potential with somewhat larger and elongated seeds that have "normal" oil chemistry. 'Hull' is a late maturity (150+ days) jumbo runner seed size, high oleic cultivar with excellent pod yields and multiple disease resistance in Florida studies. 'Hull' has resistance to TSWV and late leaf spot similar to 'C-99R' but better than 'Georgia Green'. It has white mold resistance equal to or better than C-99R and better than 'Georgia Green'. 'Hull' also has some good resistance to CBR and some root knot nematode resistance. Its seed size is similar to 'C-99R', with somewhat less vine growth. The major advantage of this new peanut is its greatly improved oil chemistry compared to all normal chemistry varieties. High oleic varieties have about 80% oleic and only 2-3% linoleic fatty acid based on total fat content, which greatly improves shelf life of products made from seed of this variety. 'GP-1' has early maturity (125-130 days) in Florida test with high oleic oil chemistry, runner seed size, and intermediate runner growth habit. 'GP-1' has some TSWV resistance but less than 'Georgia Green'. Pod yields have been equal to 'GA Green' only in low TSWV pressure situations however seed size is somewhat larger (Gorbet et al. 2002).

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14 'AP-3' is a new variety of peanut that was released in 2003 by Dr. D. W. Gorbet and will only be marketed by Anderson's Peanut Co. This variety is a medium maturity (135-140 days) with runner growth habits. It is a sister line of 'Carver' and 'NC 3033' variety developed by North Carolina with good yield. It has excellent TSWV resistance, good white mold and CBR resistance better than that of 'Carver' variety. 'AP-3' is not a high oleic variety. The grading of this variety is slightly lower than that of 'Carver' mainly due to the thicker hull of 'AP-3'. 'UF00324' is a new variety not yet approved for release and is still under evaluation. It's a medium maturity (135-140 days) variety with runner growth habits, good yield and grades similar to 'Carver' with larger seed size. 'UF00324' has good TSWV resistance similar to 'Carver'. This variety is not high oleic and it's not yet known if there is resistance to white mold or CBR. Summary Because of previous research results and the high value of peanut, growers have been reluctant to implement reduce rate herbicide application. However, with the recent introduction of new herbicides and change in government program that lowered the value of peanut, growers are now interested in reducing input costs, especially cost of weed management. With the benefits of twin-row planting including more rapid canopy closure, reduce TSWV, higher yields, and increase grade leading to increased revenue, research to determine effectiveness of reduced herbicide rates in a twin row system appears justified. Since twin row pattern achieves canopy cover at least two weeks earlier than conventional row spacing, weed suppression is possible and may require less herbicide inputs.

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15 Minimal research has been conducted in the area of reduced herbicide rates in both conventional and twin-row spacing regimes. The goal of this research was to evaluate diclosulam, flumioxazin, and imazapic for weed management and peanut yield applied at reduced rates to both twin and single row spacing production systems. Economic analysis was also conducted for these two situations. In addition, a study was conducted with commonly used herbicides used in reduced cost combinations for peanut weed management. An additional test evaluated seven new peanut cultivars for response to various commonly used herbicides.

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CHAPTER 2 EFFECTS OF REDUCED APPLICATIONS OF DICLOSULAM, FLUMIOXAZIN, AND IMAZAPIC ON WEED MANAGEMENT IN PEANUT (ARACHIS HYPOGAEA L.) PRODUCTION Introduction Peanut is a high management, high input crop with the input costs steadily increasing. Overall, yields have not increased for several years, even with new varieties and technological advances. To remain competitive in a global market, farmers must find ways to improve production efficiency or increase yields (Wright et.al 2002). Reducing the amount of herbicides applied can help reduce the 36% of production cost due to pesticide applications (Aerts 2000). Imazapic, diclosulam and flumioxazin alone and in mixtures provided control of many broadleaf weeds in peanut when applied at the full label rates (Troxler et al.2001). Weed control has been successful at these rates. Research has also been conducted using these same three herbicides but at reduced rates in peanut in an attempt to maintain weed control while reducing cost and to reduce the potential for imazapic carryover (Baughman et al.2003; Swann et al. 2000). Swann (2000) reported that diclosulam applied at 8.8 (.33X) (0.33 of the labeled rate), 17.7 (.66X), and 26.5 (1X)g ai/ha to peanut controlled yellow nutsedge (Cyperus esculentus L.) >83% and control of common ragweed (Ambrosia artemisiifolia L.) was >78%. When reduced rates of diclosulam were followed by imazapic applied early postemergence, also at reduced rates, yellow nutsedge control increased to 88% and common ragweed control increased to 99% (Swann 2000). 16

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17 Troxler et al. (2001) conducted a study using diclosulam applied at 13 g/ha (1/2x) and flumioxazin applied at 52 g ai/ha (1/2x). He concluded that weed control was comparable to the 1X rates for the two herbicides for all weeds evaluated. When diclosulam and flumioxazin applied at 1/2x were followed by imazapic applied at 35 g/ha (1/2x) weed control was similar to that observed with the regional standard. In Northwest Texas at one location, yellow nutsedge control was at least 85% with imazapic applied at the 1/2X rate in combination with diclosulam at the 1/2X rate at one location while at a second location control of yellow nutsedge was less than 70%. In South Texas, imazapic applied alone at the 1/2X rate or in combination with diclosulam at 1/2X rate controlled Palmer amaranth (Amaranthus palmeri S.), smellmellon (Cucumis melo L), and yellow nutsedge at least 80% (Baughman et al. 2003). Improving production efficiency and yield is essential for peanut producers to remain competitive. Closer spacing of rows, one way to improve yield, has been studied since the early 1900's but was not adopted by farmers until recently. More recent studies indicate that planting peanut in a twin-row spacing pattern increase yields, decrease incidents of Tomato Spotted Wilt Virus (TSWV), and may increase grade by 1 to 2%. This planting scheme results in quicker canopy coverage (as much as 2 wk earlier) which aids in weed control and results in higher grade since peanut tends to put on more of a taproot crop and less of a limb crop (Wright et al. 2001). In 1986, Cardina et al. studied weed control using reduced rates of standard herbicides on 'Sunbelt runner' planted in twin-row patterns. A 30-60% reduction in residual herbicide rates resulted in weed control and crop yield equivalent to the standard treatment. He concluded that there was

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18 potential for reducing herbicide inputs in twin-row peanut without sacrificing yield or quality (Cardina et al.1986). Because previous research indicated sometimes negative results and the high value of peanut, growers were reluctant to implement reduced rate herbicide application. However, with the recent introduction of new herbicides and change in government program that lowered the value of peanut, growers are now interested in reducing input costs, especially cost of weed management. In a more recent study, sicklepod (Senna obtusifolius L.) density in plots treated with dimethenamid-P alone was approximately 2/m2 in 2001 and 40/m2 in 2002. Sicklepod control was 10% higher in twin rows compared with single rows when evaluated late in the growing season (Lanier et al. 2003). With the benefits of twin-row planting including more rapid canopy closure, reduced TSWV, higher yields, and increased grade leading to increased revenue, research to determine effectiveness of reduced herbicide rates in twin rows appears justified. Studies conducted thus far have focused on comparing one-half with full rate application combinations of herbicides. With new interest in reducing input cost, the objective of this study was to determine if adequate weed management could be achieved in peanut at rates lower than 1/2x combinations of diclosulam, flumioxazin, and imazapic in both single and twin-row spacing. Materials and Methods Field studies were conducted in 2002 and 2003 at the West Florida Research and Education Center near Jay, FL, the North Florida Research and Education Center near Marianna, FL, and at the Plant Science Research and Education Center near Citra, FL. Jay is located in the far West panhandle of Florida with soil type of Red Bay Sand Loam

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19 (fine-loamy, siliceous, thermic, Rhodic paleudults) at pH 5.8 and organic matter of 2.1%. Marianna is located in the central panhandle with Chipola loamy sand (loamy, siliceous, thermic, Arenic hapudult) soil type containing 1.0% organic matter and pH of 6.2. Citra is located in North Central Florida with soil type Sparr sand (loamy, siliceous, hyperthermic, Grossa-renic paleudult) with organic matter 1% and pH of 6.4. Conventional tillage system consisting of deep moldboard plowing, leveling disking and one field cultivation prior to planting was used to prepare the field for peanut planting. Pendimethalin was applied at 1.12 kg ai/ha pre plant incorporated (PPI) to the entire test at all locations for control of small-seeded broadleaf and annual grasses. The peanut variety C-99R was planted on May 6, 8, and 9, 2002 at Marianna, Citra, and Jay, FL, respectively and on April 30 and May 5, 2003 at Citra and Jay FL respectively. Peanut was planted at a depth of 6 cm with a seeding rate of 122 kg/ha. Row spacing was 91cm single rows in 2002 at Jay, Citra and Marianna and in 2003 at Jay and Citra. In 2003, peanut were also planted in twin rows 20 cm apart on 91 cm spacing in addition to the single row test at Jay and Citra. Plots at Citra were four rows, 3 m wide and 6.1 m long. Plots at Jay and Marianna were four rows, 3 m wide and 7 m long. Treatments were arranged in a randomized complete block design with 4 replications. Soil fertilization and liming practices were in accordance with test recommendations by the University of Florida Soil Testing Laboratory. Florida Cooperative Extension Service recommendations were followed for management of fungicide, insecticide, and irrigation. Herbicide treatments and application rates are listed in tables 2.1 and 2.2 include diclosulam and flumioxazin applied preemergence (PRE) alone and as tank mixtures at

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20 1/4, 1/2, and full labeled rates. Imazapic at 1/4, 1/2, 2/3, and full labeled rates early postemergence (EPOST) following PRE diclosulam and/or flumioxazin treatments. All EPOST applications of imazapic included a non-ionic surfactant (Induce) of 0.25 % V/V. Herbicides were applied with a CO2 pressurized backpack sprayer calibrated to deliver 187 L/ha. Weed control was visually evaluated using a scale of 0 (no control) to 100 (complete control) early season ~35 days after planting (DAP), and late season, ~120 DAP, during the growing season. The center two rows from each plot were harvested with conventional equipment approximately 140-148 DAP at physiological maturity as determined by the hull scrape method (Johnson 1987). Plot yields were converted to yield per hectare at 8% moisture. Economic returns were determined for each treatment based on yield per hectare utilizing the following formula: Yield/hectare @ $0.50 per kg $1358/ha (total production cost) herbicide cost/ha The price per ton and total production cost was based on the average Florida peanut grower values as determined through conversation with University of Florida's Extension Agricultural Economist. Herbicide prices used in the analysis were obtained from several farm supply stores throughout Florida's peanut production region. SAS (1996) Proc GLM software was used to analyze the data. Data were subjected to analysis of variance to test treatment effects and interactions. Means were separated using Fisher's Protected LSD Test at the p<0.1 level.

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21 Results and Discussion Treatments in 2002 were different from 2003 and location interactions for all parameters measured prevented pooling of data. Therefore, data is presented by location and year. Weed Control-2002 Predominant weeds at Jay were common cocklebur (Xanthium strumarium L), sicklepod (Senna obtusifolia L.), and yellow nutsedge (Cyperus esculentus L.). Diclosulam and flumioxazin at all rates applied alone did not adequately control the weed species present (Table 2.4). Diclosulam at 1/4x and 1x PRE controlled yellow nutsedge 48 and 63% and sicklepod 9 and 25% greater than 1/4 and 1x rates of flumioxazin. Diclosulam mixed with flumioxazin both at 1/4x increased sicklepod control over diclosulam alone at 1/4x or flumioxazin alone at 1/4x and 1x rate. Preemergence treatments followed by imazapic EPOST provided better control (85%) than PRE alone for sicklepod and yellow nutsedge. Diclosulam mixed with flumioxazin at 1/4x PRE followed by imazapic at 1x EPOST provided weed control equal to the 1x rates of PRE and EPOST herbicides. Diclosulam plus flumioxazin applied PRE at 1/4x followed by imazapic at 1/2x was the lowest level of herbicide input that provided greater than 85% control of all weeds evaluated late season. Results with this treatment were comparable to that observed with the regional standard. Predominant weeds at Citra were pigweed (Amaranthus spp.), hairy indigo (Indigofera hirsuta L.), and Florida beggarweed (Desmodium tortuosum (Sw) DC.). Flumioxazin at the full rate alone PRE provided 95% control over all weeds evaluated (Table 2.5). Other PRE treatments alone did not provide weed control >72% for hairy

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22 indigo and Florida beggarweed; however, control was ~20% greater with flumioxazin than with diclosulam. Diclosulam plus flumioxazin applied PRE both at 1/4x followed by imazapic at 2/3x was the lowest level of herbicide input that provided greater than 90% late season control of all weeds evaluated and greater than 1x treatments. Smallflower morningglory (Jaquemontia tamnifolia (L.) Greseb), and tropic croton (Croton glandulosus L.) control at Marianna was greater than 85% for all treatments except flumioxazin at 1/4x PRE fb imazapic at 1/4x EPOST (Table 2.6). However, none of the treatments provided >60% control of yellow nutsedge and only Diclosulam at 1x plus flumioxazin at 1x PRE fb imazapic at 1x provided >70% sicklepod control. Lack of control was due to rain soon after the EPOST application of imazapic which requires at least a 3 hour rain free period (Cadre 2001). Weed Control-2003 Citra represented an area of relatively low weed pressure at approximately 1-3 weeds per m2 in the untreated checks for all but one species. The one species present at a higher population (2 to 10 weeds per m2) is a new troublesome weed to Florida and parts of Georgia in both cotton and peanut; tropical spiderwort (Commelina benghalensis L.). This weed establishes quickly, and has prostrate growth therefore providing quick ground cover, and is difficult to control. Quick growth and establishment of this weed may have reduced the populations of the other weeds. All treatments in both twin-and single-row studies provided 77% or greater control of sicklepod, purple nutsedge (Cyperus rotundus L.), hairy indigo, and cutleaf groundcherry (Physalis angulata L.) (Tables 2.7 and 2.8). Florida beggarweed control was greater than 80% for all treatments except for diclosulam PRE treatments applied

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23 alone at all rates in both the twin-and single-row studies and treatments with diclosulam PRE at 1/4 and 1/2x followed by imazapic at 1/4x, flumioxazin at 1/2x followed by imazapic at 1x, and imazapic alone EPOST at 1/4x in the single-row study. Tropical spiderwort was the predominant weed at Citra. Tropical spiderwort was controlled >80% in more treatments in the twin-row study than in the single-row study. Diclosulam 1/4x applied with flumioxazin at 1/4x PRE followed by imazapic EPOST at 1/4x was the least herbicide input that provided greater than 80% tropical spiderwort control in twin rows. In single rows diclosulam combined with flumioxazin PRE followed by imazapic EPOST all at 1/2x was the herbicide combination that provided 86% control. Jay was an area of relatively high weed pressure. Predominate weeds at this location were sicklepod, purple nutsedge, Florida beggarweed, smallflower morningglory, and wild poinsettia (Euphorbia heterophylla L.). All treatments in both twin-and single-row studies provided greater than 87% control for smallflower morningglory and wild poinsettia (Table 2.9 and 2.10). Full rate treatments and the regional standard were required to control sicklepod greater than 85% in both row spacing studies as was expected from previous experience with these three herbicides (Prostko and Gray 2003 & 2004). Florida beggarweed control late-season was greater than 85% in the single-row study except for diclosulam PRE alone at all rates, diclosulam followed by imazapic at 1/4x, and when imazapic was applied alone EPOST at 1/4 and 1/2x. Flumioxazin at all rates alone or when followed by imazapic provided greater than 89% control late-season. Twin-row culture provided increased control (greater than 85%) of Florida beggarweed as opposed to the single-row system. Treatments with

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24 diclosulam 1/4x PRE or imazapic 1/4x EPOST provided 77 and 80% control respectively. Diclosulam at 1/4x applied with flumioxazin at 1/4x PRE was the only treatment in the twin-row culture that provided less than 84% control of purple nutsedge. Control of purple nutsedge was greater with diclosulam than with flumioxazin applied alone for all rates in the single-row system. Peanut Yield There was no significant difference among treatments at Jay, Marianna, or Citra in 2002. Yield was much lower at Jay in 2002. This was due to a late-season infestation of Cylindrocladium black rot (Cylindrocladium parasiticum) and the heavy rains from a tropical storm that delayed drying and harvesting after digging and inverting was complete. Flumioxazin at 1x yielded 1582 kg/ha more than flumioxazin at 1/4x (Table 2.11). Yield at Citra ranged from 2571 to 4459 kg/ha (non-treated and diclosulam with flumioxazin at 1/4x, respectively) (Table 2.11). Flumioxazin applied at 1/4x PRE yielded 1253 kg/ha less than the highest yielding treatment, yielding only higher than the non-treated control. Other treatments were not significantly different. Yield at Marianna was the highest for treatments with flumioxazin at 1/4x PRE followed by imazapic at 1/2x and flumioxazin plus diclosulam at 1/4x PRE followed by imazapic at 1/4x EPOST (4902 and 4953 kg/ha, respectively) (Table 2.12). The non-treated control yielded lowest at 3885kg/ha. In 2003, there again was no significant difference among treatments (Table 2.14). Diclosulam mixed with flumioxazin at 1/2x followed by imazapic at 1/2x treatment was the highest yielding in the single row study at both locations (6811and 4824 kg/ha). This treatment was also among the higher yielding (3rd and 4th) treatments in the twin row study. The highest yielding treatments in both twin row studies were observed with

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25 imazapic at 1/4x alone EPOST, flumioxazin at 1/4x alone PRE, and diclosulam at 1/4x PRE followed by imazapic at 1/2x EPOST. Applications of imazapic EPOST following a PRE application consistently resulted in increased yield (~300 kg/ha) at both locations and in both row patterns except at Citra for flumioxazin applied PRE where the weed pressure was low. Economic Analysis Total revenue at Citra and Jay in the single row study was highest with diclosulam plus flumioxazin both at 1/2x followed by imazapic at 1/2x ($1981.68 and $986.00/ha, respectively) (Table 2.14). The next highest return was with the combination of diclosulam plus flumioxazin 1/4x followed by imazapic at 1x at Citra and flumioxazin applied at 1/4x followed by imazapic at 1/2x at Jay ($1929.02 and $968.71/ha, respectively). The highest total revenue in the Citra twin-row study was with imazapic applied at 1/4x EPOST and next highest was with flumioxazin at 1/4x ($1770.30 and $1701.43/ha, respectively). The lowest total revenue was observed with flumioxazin followed by imazapic at 1x in the twin row study and diclosulam applied with flumioxazin at 1/4x followed by imazapic at 2/3x in the single-row study ($656.49 and $961.21/ha, respectively). Total revenue at Jay was highest with diclosulam mixed with flumioxazin at 1/4x followed by imazapic at 1x ($864.68/ha). Results from these studies indicate reduced rates of diclosulam and flumioxazin followed by imazapic can be used in Florida peanut production, provide adequate weed control without compromising yield and provide total revenue equal to or higher than the regional standard. Diclosulam applied with flumioxazin PRE followed by imazapic EPOST at 1/2x consistently (both years in twin-and single-row systems) produced total

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26 revenue higher than the regional standard of paraquat plus bentazone AC fb imazapic EPOST with treatment cost $3 less per hectare. Since the passing of the 2002 Farm Bill, growers will have to compete in a global market receiving the world price for their peanut which is significantly lower than the previous government supported price. Peanut are a high management, high input crop with the cost of inputs steadily increasing. To remain competitive, growers must find ways in which to improve production efficiency. Reducing the amount of herbicides applied is one way to reduce the 40% of total production cost that results from pesticides (Aerts an Nesheim 2000). Further research is needed to determine whether using reduced rates of imazapic may decrease the potential for carryover to the next growing season so that rotational restriction on cotton for the following year might be relaxed. Environmental effects such as leaching of chemicals and ground water quality may also be reduced due to the lower herbicide rates. With all the benefits of increased yield, increased grade, decreased TSWV, and decreased weed populations proven in previous studies with twin-row planting regimes, the additional benefit of effectively using reduced rates of herbicides can only result in an increase in total revenue. They benefit the grower, consumer, and the U.S. economy since peanut contributes over $4 billion to the economy each year (USDA 2002).

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27 Table 2.1-2002 Reduced rate treatments-Jay and Citra, FL. Abbreviation Treatment a,b Rate Portion of labeled rate Timingc g ai/ha Check NONTREATED DS Diclosulam 6.72 1/4x PRE DS Diclosulam 26.8 1x PRE FL Flumioxazin 26.3 1/4x PRE FL Flumioxazin 105.3 1x PRE FL + Flumioxazin + 26.3 1/4x PRE + DS Diclosulam 6.72 1/4x PRE FL + Flumioxazin + 26.3 1/4x PRE + DS fb Diclosulam fb 6.72 1/4x PRE fb IM Imazapic 35.3 1/2x EPOST FL+ Flumioxazin + 26.3 1/4x PRE + DS fb Diclosulam fb 6.72 1/4x PRE fb IM Imazapic 47.1 2/3x EPOST DS fb Diclosulam fb 26.8 1x PRE fb IM Imazapic 70.6 1x EPOST FL fb Flumioxazin fb 105.3 1x PRE fb IM Imazapic 70.6 1x EPOST FL+ Flumioxazin + 26.3 1/4x PRE + DS fb Diclosulam fb 6.72 1/4x PRE fb IM Imazapic 70.6 1x EPOST PAR+ Paraquat + 140 1x PRE + BEN fb Bentazon fb 280 1x PRE fb IM Imazapic 70.6 1x EPOST a All treatments including the check received pendimethalin PPI @ 1120 g ai/ha b EPOST applications received surfactant at 0.25% V/V. c + = tank mix, fb = followed by in a sequential treatment

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28 Table 2.2 Reduced rate treatmentsMarianna, FL Abbreviation Treatment a,b Rate Portion of labeled rate Timingc g ai/ha Check Non-treated DS fb IM diclosulam fb imazapic 6.72 17.6 1/4x 1/4x PRE fb EPOST DS fb IM diclosulam fb imazapic 6.72 35.3 1/4x 1/2x PRE fb EPOST DS fb IM diclosulam fb imazapic 13.4 17.6 1/2x 1/4x PRE fb EPOST DS fb IM diclosulam fb imazapic 13.4 35.3 1/2x 1/2x PRE fb EPOST FL fb flumioxazin fb 26.3 1/4x PRE fb IM imazapic 17.6 1/4x EPOST FL fb flumioxazin fb 26.3 1/4x PRE fb IM imazapic 35.3 1/2x EPOST FL fb flumioxazin fb 52.6 1/2x PRE fb IM imazapic 17.6 1/4x EPOST FL fb flumioxazin fb 52.6 1/2x PRE fb IM imazapic 35.3 1/2x EPOST DS+ FL fb diclosulam + flumioxazin fb 6.72 26.3 1/4x 1/4x PRE + PRE fb IM DS+ Imazapic diclosulam + 17.6 13.4 1/4x 1/2x EPOST PRE + FL fb IM DS+ FL fb flumioxazin fb imazapic diclosualm + flumioxazin fb 52.6 35.3 26.8 105.3 1/2x 1/2x 1x 1x PRE fb EPOST PRE + PRE fb IM imazapic 70.6 1x EPOST a All treatments including the check received pendimethalin PPI @ 1120 g ai/ha b EPOST applications received surfactant at 0.25% V/V. c + = tank mix, fb = followed by in a sequential treatment

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29 Table 2.3-2003 Reduced rate treatmentsJay and Citra, FL. Abbreviation Treatment a,b Rate Portion of labeled rate g ai/ha Timingc Check Non-treated DS diclosulam 6.72 1/4x PRE DS diclosulam 13.4 1/2x PRE DS diclosulam 26.8 1x PRE DS fb diclosulam fb 6.72 1/4x PRE fb IM imazapic 17.6 1/4x EPOST DS fb diclosulam fb 6.72 1/4x PRE fb IM imazapic 35.3 1/2x EPOST DS fb diclosulam fb 13.4 1/2x PRE fb IM imazapic 17.6 1/4x EPOST DS fb diclosulam fb 13.4 1/2x PRE IM imazapic 35.3 1/2x EPOST DS fb diclosulam fb 13.4 1/2x PRE fb IM imazapic 70.6 1x EPOST DS fb diclosulam fb 26.8 1x PRE fb IM imazapic 70.6 1x EPOST FL flumioxazin 26.3 1/4x PRE FL flumioxazin 52.6 1/2x PRE FL flumioxazin 105.3 1x PRE FL fb flumioxazin fb 26.3 1/4x PRE fb IM imazapic 17.6 1/4x EPOST FL fb flumioxazin fb 26.3 1/4x PRE fb IM imazapic 35.3 1/2x EPOST FL fb flumioxazin fb 52.6 1/2x PRE fb IM imazapic 17.6 1/4x EPOST FL fb flumioxazin fb 52.6 1/2x PRE fb IM imazapic 35.3 1/2x EPOST

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30 Table 2.3 Continued Abbreviation Treatment a,b Rate Portion of labeled rate g ai/ha Timingc FL fb flumioxazin fb 52.6 1/2x PRE fb IM imazapic 70.6 1x EPOST FL fb flumioxazin fb 105.3 1x PRE fb IM imazapic 70.6 1x EPOST FL fb flumioxazin + 26.3 1/4x PRE + DS diclosulam 6.72 1/4x PRE FL+ flumioxazin + 26.3 1/4x PRE + DS fb diclosulam fb 6.72 1/4x PRE fb IM imazapic 17.6 1/4x EPOST FL+ flumioxazin + 26.3 1/4x PRE + DS fb diclosulam fb 6.72 1/4x PRE fb IM imazapic 35.3 1/2x EPOST FL+ flumioxazin + 26.3 1/4x PRE + DS fb diclosulam fb 6.72 1/4x PRE fb IM imazapic 47.1 2/3x EPOST FL+ flumioxazin + 26.3 1/4x PRE + DS fb diclosulam fb 6.72 1/4x PRE fb IM imazapic 70.6 1x EPOST FL+ flumioxazin + 52.6 1/2x PRE + DS fb diclosulam fb 13.4 1/2x PRE fb IM imazapic 35.3 1/2x EPOST FL + flumioxazin + 105.3 1x PRE + DS fb diclosulam fb 26.8 1x PRE fb IM imazapic 70.6 1x EPOST IM imazapic 17.6 1/4x EPOST IM imazapic 35.3 1/2x EPOST Para + paraquat + 140 AC + Ben fb bentazon fb 280 AC fb IM imazapic 70.6 EPOST a All treatments including the check received pendimethalin PPI @ 1120 g ai/ha b EPOST applications received surfactant at 0.25% V/V. c + = tank mix, fb = followed by in a sequential treatment

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31 Table 2.4Weed control as affected by reduced rate herbicide treatments in 2002 at Jay, FL Late Seasona TRTb,c,d XANST CASOB CYPES ------------------------% Control--------------------------------------Check 0 0 0 DS 1/4x 86 45 76 DS 1x 97 72 93 FL 1/4x 65 36 28 FL 1x 75 47 30 DS + FL1/4x 88 70 75 DS + FL 1/4x fb 97 85 95 IM 1/2x DS + FL 1/4x fb 95 86 97 IM 2/3x DS + IM 1x 97 95 100 FL + IM 1x 97 95 100 DS + FL fb 98 92 100 IM 1/2x Par + Ben 1x fb 87 97 100 IM 1x LSDe 18.2 18.5 20 a XANST Xanthuim strumarium CASOB Senna obtusifolia CYPES Cyperus esculentus b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120 g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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32 Table 2.5-Weed control as affected by reduced rate herbicide treatments in 2002 at Citra, FL Late Season a TRT b,c,d AMASP INDHI DEDTO -----------------% Control---------------------------Check 0 0 0 DS 1/4x 92 52 52 DS 1x 93 67 67 FL 1/4x 41 72 72 FL 1x 95 95 95 DS + FL1/4x 92 78 78 DS + FL 1/4x fb 93 71 71 IM 1/2x DS + FL 1/4x fb 93 93 93 IM 2/3x DS + IM 1x 92 70 70 FL + IM 1x 91 86 86 DS + FL fb 40 83 83 IM 1/2x LSD e 6.2 24.2 24.2 a AMASP Amaranthus spp INDHI Indigofera hirsute DEDTO Desmodium tortuosum b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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33 Table 2.6-Weed control as affected by reduced rate herbicide treatments in 2002 at Marianna, FL Late Season a TRT b,c,d CYPES IAQTA CASOB CVNGL -------------------------% Control-----------------------------DS 1/4x fb IM 1/4x 32 99 26 89 DS 1/4x fb IM 1/2x 32 99 35 99 DS 1/2x fb IM 1/4x 21 99 35 99 DS 1/2x fb IM 1/2x 35 99 40 99 FL 1/4x fb IM 1/4x 12 73 12 99 FL 1/4x fb IM 1/2x 27 89 40 86 FL 1/2x fb IM 1/4x 35 95 30 99 FL 1/2x fb IM 1/2x 30 96 18 99 DS 1/4x + FL 1/4x fb 27 99 37 99 IM 1/4x DS 1/2x + FL 1/2x fb 57 99 55 99 IM 1/2x DS 1x + FL 1x fb 55 99 72 99 IM 1x Check 0 0 0 0 LSD e 20.4 9.2 21.7 10.9 a IAQTA Jaquemontia tamnifolia CVNGL Croton glandulosus CASOB Senna obtusifolia CYPES Cyperus esculentus b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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34 Table 2.7-Weed control as affected by reduced rate herbicide treatments in 2003 at Citra, FL in single row study Late Season a TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBA --------------------------------% Control-----------------------------------DS 1/4x 96 99 74 77 87 67 DS 1/2x 91 96 68 97 99 75 DS 1x 84 96 84 93 98 80 DS1/4x fb IM 1/4x 91 95 72 97 99 68 DS 1/4x fb IM 1/2x 94 99 93 97 99 72 DS 1/2x fb IM 1/4x 99 99 72 93 99 75 DS 1/2x fb IM 1/2x 99 99 89 89 99 82 DS 1/2x fb IM 1x 99 99 95 97 99 82 DS 1x fb IM 1x 96 99 99 94 99 90 Check 0 0 0 0 0 0 FL 1/4x 86 86 84 94 99 58 FL 1/2x 84 95 94 97 99 58 FL 1x 90 96 86 94 99 66 FL 1/4x fb IM 1/4x 96 90 90 97 99 53 FL 1/4x fb IM 1/2x 99 99 88 94 99 57 FL 1/2x fb IM 1/4x 99 96 94 97 99 57 FL 1/2x fb IM 1/2x 99 99 99 97 99 71 FL 1/2x fb IM 1x 99 99 76 96 99 78 FL 1x fb IM 1x 95 99 96 97 99 73 DS 1/4x + FL 1/4x 99 96 99 96 99 71 DS 1/4x + FL 1/4x fb IM 1/4x 95 99 99 94 99 76 DS 1/4x + FL 1/4x fb IM 1/2x 94 99 99 97 99 22 DS 1/4x + Fl 1/4x fb IM 2/3x 99 99 96 97 99 75 DS 1/4x + FL 1/4x fb IM 1x 93 99 96 96 99 87 DS 1/2x + FL 1/2x fb IM 1/2x 91 99 93 94 99 86 DS 1x + FL 1x fb IM 1x 99 99 99 97 99 91 IM 1/4x 99 96 99 97 99 68 IM 1/2x 93 76 65 94 99 52

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35 Table 2.7 Continued Late Season a TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBA --------------------------------% Control-----------------------------------Par 1x + Ben 1x fb IM 1x 99 99 91 97 99 75 Check 0 0 0 0 0 0 LSD e 12.8 11 22.7 6.4 2.5 19.2 a CASOB Senna obtusifolia CYPRO Cyperus rotundus INDHI Indigofera hirsute DEDTO Desmodium tortuosum PHYAN Physalis angulata COMBA Commelina banghalensis b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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36 Table 2.8-Weed control as affected by reduced rate herbicide treatments in 2003 at Citra, FL in twin row study Late Season a TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBA --------------------------------% Control---------------------------------DS 1/4x 77 94 75 94 86 83 DS 1/2x 77 88 76 90 89 82 DS 1x 80 96 76 88 99 77 DS1/4x fb IM 1/4x 86 94 86 99 86 82 DS 1/4x fb IM 1/2x 86 99 85 99 99 81 DS 1/2x fb IM 1/4x 94 96 92 91 99 63 DS 1/2x fb IM 1/2x 92 96 94 99 99 77 DS 1/2x fb IM 1x 92 99 94 99 99 82 DS 1x fb IM 1x 92 99 92 99 96 91 Check 0 0 0 0 0 0 FL 1/4x 94 84 88 94 96 60 FL 1/2x 92 79 91 97 99 66 FL 1x 92 96 94 94 99 85 FL 1/4x fb IM 1/4x 94 96 94 97 99 70 FL 1/4x fb IM 1/2x 92 99 94 94 99 75 FL 1/2x fb IM 1/4x 92 94 94 97 99 67 FL 1/2x fb IM 1/2x 92 93 94 97 99 76 FL 1/2x fb IM 1x 92 95 92 96 99 87 FL 1x fb IM 1x 94 99 94 97 91 85 DS 1/4x + FL 1/4x 92 93 92 96 99 76 DS 1/4x + FL 1/4x fb IM 1/4x 92 96 94 94 99 83 DS 1/4x + FL 1/4x fb IM 1/2x 92 99 94 97 99 83 DS 1/4x + Fl 1/4x fb IM 2/3x 92 92 94 97 99 85 DS 1/4x + FL 1/4x fb IM 1x 92 99 87 96 99 86 DS 1/2x + FL 1/2x fb IM 1/2x 92 99 94 94 99 90 DS 1x + FL 1x fb IM 1x 92 98 92 97 99 88 IM 1/4x 92 95 92 97 99 86 IM 1/2x 92 91 89 94 99 88

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37 Table 2.8 Continued Late Season a TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBA --------------------------------% Control---------------------------------Par 1x + Ben 1x fb IM 1x 92 99 94 97 99 92 Check 0 0 0 0 0 0 LSD e 10.3 9.2 10.7 5.8 8.3 16.7 a CASOB Senna obtusifolia CYPRO Cyperus rotundus INDHI Indigofera hirsute DEDTO Desmodium tortuosum PHYAN Physalis angulata COMBA Commelina banghalensis b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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38 Table 2.9-Weed control as affected by reduced rate herbicide treatments in 2003 at Jay, FL in single row study Late Season a TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL -----------------------------% Control-----------------------------------DS 1/4x 30 78 77 87 96 DS 1/2x 43 86 94 99 99 DS 1x 65 99 89 94 99 DS1/4x fb IM 1/4x 52 85 64 96 94 DS 1/4x fb IM 1/2x 68 99 93 99 99 DS 1/2x fb IM 1/4x 48 94 78 99 99 DS 1/2x fb IM 1/2x 59 99 93 99 99 DS 1/2x fb IM 1x 75 99 99 99 99 DS 1x fb IM 1x 85 99 88 99 99 Check 0 0 0 0 0 FL 1/4x 51 62 89 86 89 FL 1/2x 63 76 90 90 90 FL 1x 94 67 85 96 91 FL 1/4x fb IM 1/4x 55 94 93 99 96 FL 1/4x fb IM 1/2x 68 96 99 99 99 FL 1/2x fb IM 1/4x 62 81 99 99 99 FL 1/2x fb IM 1/2x 76 99 91 99 99 FL 1/2x fb IM 1x 73 99 94 99 96 FL 1x fb IM 1x 89 99 99 99 99 DS 1/4x + FL 1/4x 40 95 99 94 94 DS 1/4x + FL 1/4x fb IM 1/4x 61 90 99 93 96 DS 1/4x + FL 1/4x fb IM 1/2x 61 99 99 96 99 DS 1/4x + Fl 1/4x fb IM 2/3x 63 99 99 99 99 DS 1/4x + FL 1/4x fb IM 1x 66 99 99 99 99 DS 1/2x + FL 1/2x fb IM 1/2x 69 99 99 99 99 DS 1x + FL 1x fb

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39 Table 2.9 Continued Late Season a TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL -----------------------------% Control-----------------------------------IM 1x 89 99 99 99 99 IM 1/4x 47 96 75 99 69 IM 1/2x 67 94 73 99 88 Par 1x + Ben 1x fb IM 1x 96 99 99 99 99 Check 0 0 0 0 0 LSD e 18.3 10.9 15.2 5 8 a CASOB Senna obtusifolia, CYPRO Cyperus rotundus, DEDTO Desmodium tortuosum, IAQTA Jaquemontia tamnifolia, EPHHL Euphorbia heterophylla b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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40 Table 2.10-Weed control as affected by reduced rate herbicide treatments in 2003 at Jay, FL in twin row study Late Season a TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL -----------------------------% Control-----------------------------------DS 1/4x 51 88 77 99 94 DS 1/2x 43 99 94 99 99 DS 1x 45 96 84 99 96 DS1/4x fb IM 1/4x 50 99 88 99 96 DS 1/4x fb IM 1/2x 79 99 94 99 99 DS 1/2x fb IM 1/4x 60 99 99 99 99 DS 1/2x fb IM 1/2x 66 99 99 99 96 DS 1/2x fb IM 1x 77 99 94 99 96 DS 1x fb IM 1x 73 96 75 99 88 Check 0 0 0 0 0 FL 1/4x 58 84 99 99 96 FL 1/2x 53 90 99 99 96 FL 1x 56 94 93 99 96 FL 1/4x fb IM 1/4x 53 93 99 99 96 FL 1/4x fb IM 1/2x 71 99 94 99 99 FL 1/2x fb IM 1/4x 62 94 85 99 99 FL 1/2x fb IM 1/2x 75 99 99 99 96 FL 1/2x fb IM 1x 77 99 99 99 99 FL 1x fb IM 1x 94 99 99 99 99 DS 1/4x + FL 1/4x 27 74 91 99 96 DS 1/4x + FL 1/4x fb IM 1/4x 82 99 99 99 96 DS 1/4x + FL 1/4x fb IM 1/2x 56 99 99 99 99 DS 1/4x + Fl 1/4x fb IM 2/3x 74 99 99 99 99 DS 1/4x + FL 1/4x fb IM 1x 73 99 94 99 99 DS 1/2x + FL 1/2x fb IM 1/2x 65 99 99 99 99 DS 1x + FL 1x fb IM 1x 94 99 99 99 99 IM 1/4x 53 99 80 99 96 IM 1/2x 67 99 90 99 89

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41 Table 2.10 Continued Late Season a TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL -----------------------------% Control-----------------------------------Par 1x + Ben 1x fb IM 1x 94 99 99 99 99 Check 0 0 0 0 0 LSD e 19 13 12 0 6 a CASOB Senna obtusifolia, CYPRO Cyperus rotundus, DEDTO Desmodium tortuosum, IAQTA Jaquemontia tamnifolia, EPHHL Euphorbia heterophylla b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d+ = tank mix, fb = followed by in a sequential treatment e Fisher's Protected LSD test P < 0.1.

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42 Table 2.11Peanut yield as affected by reduced herbicide treatments in 2002 at Jay and Citra, FL. Treatment a,b,c Jay Citra -------------------kg/ha-------------------Check 2529 2571 DS 1/4x 3056 4003 DS 1x 2617 4329 FL 1/4x 1992 3206 FL 1x 3574 4101 DS + FL1/4x 2882 4459 DS+FL 1/4x fb 3525 3987 IM 1/2x DS+FL 1/4x fb 2412 4329 IM 2/3x DS 1x fb IM 1x 2812 3548 FL 1x fb IM 1x 2763 3971 DS+FL 1/4x fb 2480 3792 IM 1x Par+Ben fb 3242 N/Ad IM 1x NS e NS a DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. b All treatments including the check received pendimethalin PPI @ 1120g ai/ha c+ = tank mix, fb = followed by in a sequential treatment d Regional standard treatment was not included at Citra, Fl. e P < 0.1 level.

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43 Table 2.12Peanut yield as affected by reduced herbicide treatments in 2002 at Marianna, FL. Treatment Marianna kg/ha DS 1/4x fb IM 1/4x 4780 DS 1/4x fb IM 1/2x 4333 DS 1/2x fb IM 1/4x 4434 DS 1/2x fb IM 1/2x 4048 FL 1/4x fb IM1/4x 4699 FL 1/4x fb IM 1/2x 4902 FL 1/2x fb IM 1/4x 4679 FL 1/2x fb IM 1/2x 4597 DS + FL 1/4x fb 4953 IM 1/4x DS + FL 1/2x 4506 IM 1/2x DS + FL 1/2x fb 4658 IM 1/2x Check 3885 NS d a DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. b All treatments including the check received pendimethalin PPI @ 1120g ai/ha c+ = tank mix, fb = followed by in a sequential treatment d P < 0.1 level.

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44 Table 2.13-Peanut yield as affected by reduced rate herbicide treatments in 2003 at Jay and Citra, Fl. in twin and single row studies. Citra Jay Treatment a,b,c Single Twin Single Twin ------------------------------kg/ha--------------------------------DS 1/4x 5956 5151 3700 4189 DS 1/2x 5566 5590 3574 4023 DS 1x 5859 4809 3886 4081 DS 1/4x fb IM 1/4x 6005 5444 3818 4267 DS 1/4x fb IM 1/2x 5858 5664 4052 4492 DS 1/2x fb IM 1/4x 6322 5150 4374 3544 DS 1/2x fb IM 1/2x 5761 5492 4032 4384 DS 1/2x fb IM 1x 6225 5517 4140 4433 DS 1x fb IM 1x 6420 5077 4091 3798 Check 5126 5444 3691 3642 FL 1/4x 5468 6152 3779 3974 FL 1/2x 6030 5761 4296 3613 FL 1x 6591 5834 4443 4257 FL 1/4x fb IM 1/4x 4931 5200 3866 4374 FL 1/4x fb IM 1/2x 5419 5285 4735 4081 FL 1/2x fb IM 1/4x 5785 5200 4198 4379 FL 1/2x fb IM 1/2x 6127 4150 4198 4042 FL 1/2x fb IM 1x 6371 5224 4706 4433 FL 1x fb IM 1x 6103 4199 4160 4276 DS 1/4x + FL 1/4x 6213 5834 4140 3730 DS 1/4x + FL 1/4x fb IM 1/4x 6152 5346 4550 4306 DS 1/4x + FL 1/4x fb IM 1/2x 5663 4565 4160 4023 DS 1/4x + Fl 1/4x fb IM 2/3x 4760 4882 4169 4306 DS 1/4x + FL 1/4x fb IM 1x 6713 4955 4013 4589 DS 1/2x + FL 1/2x fb IM 1/2x 6811 5932 4824 4423

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45 Table 2.13 Continued Citra Jay Treatment a,b,c Single Twin Single Twin ------------------------------kg/ha--------------------------------DS 1x + FL 1x fb IM 1x 6591 5834 3944 4384 IM 1/4x 6225 6298 4657 3984 IM 1/2x 5590 5834 4062 4072 Par 1x + Ben 1x fb IM 1x 6396 5492 4277 4404 Check 5395 5932 3837 3544 NS d NS NS NS a DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. b All treatments including the check received pendimethalin PPI @ 1120g ai/ha c+ = tank mix, fb = followed by in a sequential treatment d P < 0.1 level.

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46 Table 2.14 Total revenue per treatment as affected by yield and treatment cost separated by location and row spacing Citra, FL Jay, FL Treatment b,c,d Single Twin Single Twin --------------------------TR ($/hectare)a.-----------------------DS 1/4x 1601 1197 470 715 DS 1/2x 1395 1407 397 622 DS 1x 1522 996 533 631 DS1/4x fb IM 1/4x 1613 1332 517 742 DS 1/4x fb IM 1/2x 1529 1431 624 844 DS 1/2x fb IM 1/4x 1762 1175 786 370 DS 1/2x fb IM 1/2x 1470 1335 604 780 DS 1/2x fb IM 1x 1682 1327 637 784 DS 1x fb IM 1x 1760 1087 593 446 Check 1210 1369 491 467 FL 1/4x 1358 1701 512 610 FL 1/2x 1632 1497 763 421 FL 1x 1898 1519 822 729 FL 1/4x fb IM 1/4x 1077 1212 544 798 FL 1/4x fb IM 1/2x 1311 1244 968 640 FL 1/2x fb IM 1/4x 1498 1205 702 793 FL 1/2x fb IM 1/2x 1658 668 692 613 FL 1/2x fb IM 1x 1759 1185 925 788 FL 1x fb IM 1x 1610 656 636 695 DS 1/4x + FL 1/4x 1722 1532 683 477 DS 1/4x + FL 1/4x fb IM 1/4x 1679 1275 876 754 DS 1/4x + FL 1/4x fb IM 1/2x 1423 873 670 602 DS 1/4x + Fl 1/4x fb IM 2/3x 961 1022 665 733 DS 1/4x + FL 1/4x fb IM 1x 1929 1048 576 864 DS 1/2x + FL 1/2x fb IM 1/2x 1981 1541 986 785 DS 1x + FL 1x fb IM 1x 1815 1436 489 709 IM 1/4x 1733 1770 947 610

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47 Table 2.14 Continued Citra, FL Jay, FL Treatment b,c,d Single Twin Single Twin --------------------------TR ($/hectare)a.-----------------------IM 1/2x 1404 1526 639 644 Par 1x + Ben 1x fb IM 1x 1770 1317 709 772 Check 1345 1614 564 417 a Total revenue based on equation: yield per treatment at $0.50 per kg total production cost ($1358 per hectare) herbicide treatment cost per hectare. b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. c All treatments including the check received pendimethalin PPI @ 1120g ai/ha d + = tank mix, fb = followed by in a sequential treatment

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48 Table 2.15 Herbicide treatment cost for reduced rate study Treatment a,b $/hectare DS 1/4x 25.68 DS 1/2x 35.56 DS 1x 55.31 DS1/4x fb IM 1/4x 37.5 DS 1/4x fb IM 1/2x 48.34 DS 1/2x fb IM 1/4x 47.38 DS 1/2x fb IM 1/2x 58.22 DS 1/2x fb IM 1x 79.21 DS 1x fb IM 1x 98.96 FL 1/4x 23.34 FL 1/2x 30.89 FL 1x 45.97 FL 1/4x fb IM 1/4x 35.16 FL 1/4x fb IM 1/2x 46 FL 1/2x fb IM 1/4x 42.71 FL 1/2x fb IM 1/2x 53.55 FL 1/2x fb IM 1x 74.75 FL 1x fb IM 1x 89.62 DS 1/4x + FL 1/4x 33.22 DS 1/4x + FL 1/4x fb IM 1/4x 45.04 DS 1/4x + FL 1/4x fb IM 1/2x 55.88 DS 1/4x + Fl 1/4x fb IM 2/3x 66.03 DS 1/4x + FL 1/4x fb IM 1x 76.87 DS 1/2x + FL 1/2x fb IM 1/2x 73.31 DS 1x + FL 1x fb IM 1x 129.13 IM 1/4x 27.62 IM 1/2x 38.47 Par 1x + Ben 1x fb IM 1x 76.12 a DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g ai/ha, 1x=26.8, 105.3, 70.6g ai/ha. respectively. b + = tank mix, fb = followed by in a sequential treatment

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CHAPTER 3 EFFECTS OF REDUCED COST HERBICIDE TREATMENT COMBINATIONS ON WEED MANAGEMENT IN PEANUT (ARACHIS HYPOGAEA L.) PRODUCTION Introduction In 2002, approximately 3.19 million hectares of peanut (Arachis hypogaea L.) were harvested in the United States with an average yield of 2,870 kilograms per hectare (USDA 2002). This was a 5% reduction from 2001 and a 4% reduction from 2000. Growers in the Southwest (New Mexico, Oklahoma, and Texas) planted 180,000 hectares of peanut in 2001, 16% less than 2000. Plantings in the Virgina-North Carolina region totaled 67,000 hectares, a 17% reduction from 2001. Peanut planting in these areas was delayed due to the early dry conditions and peanut hectarage was reduced in response to the new Farm Bill, growers planted fewer dry-land peanut because they often have a lower yield potential than irrigated peanut. The Southeast (Alabama, Florida, Georgia, and South Carolina) is the largest production region of peanut in the United States with over 350,000 hectares planted in 2002, an increase of 6% from 2001 (USDA 2002). Peanut are a significant part of the row crop economy in Florida. Florida is ranked 5th nationally in production and Jackson County is the 3rd leading peanut producing county in the United States. In 2002, Florida harvested 35,000 hectares with an average yield of 2,600 kilograms per hectare (Aerts and Nesheim 2000). Since 1990 the price per kilogram received for peanut has declined considerably from $ 0.66/kg to the December 2001 price of $0.43/kg. The 2002 Farm Bill will be the 49

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50 determining factor for profitability of peanut. Growers were receiving the previous quota price of $0.67/kg but that has been reduced to $0.39/kg as a result of the 2002 Farm Bill. Pest management accounts for a large portion of the variable production cost for peanut. More than 36% of the total operating costs are invested in pesticides (Aerts and Nesheim 2000). In peanut, there are over 43 weed species, 20 insect pests, 17 disease and 4 nematode pathogens that are of economic importance in 9 peanut producing states. The worst weed pests, if left uncontrolled, can reduce yield 30-80 percent in infested areas (Aerts and Nesheim 2000). Peanut weed control is accomplished through cultural, mechanical, and chemical practices. Crop rotation has many benefits, including better weed control that is obtained when a variety of herbicides are used. Mixing two herbicides with different modes of action reduces the probability of weed resistance and shifts. Cultivation may be utilized if effective weed control with herbicides is not achieved (Ducar et al. 2002). In peanut, the most effective weed control and highest yield has generally been obtained using a herbicide program that includes a preplant incorporated (PPI) and/or preemergence (PRE) treatment, followed by an at cracking (AC) stage treatment, followed by a postemergence (POST) application (Ducar et al. 2002). Traditional herbicide applications have included pendimethalin or ethalfluralin applied PPI for control of annual grasses and small seeded broadleaf weeds followed by a PRE application of diclosulam, flumioxazin, or norflurazon for additional control of broadleaf weeds. At cracking and POST herbicides most commonly used in Florida peanut production include: paraquat for broad spectrum early season weed control; bentazon for control of yellow nutsedge (Cyperus esculentus L.) and good control of various broadleaf

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51 weeds; 2,4-DB for control of morningglory spp. (Ipomoea spp.) and sicklepod (Senna obtusifolia L.); chlorimuron or imazapic for late season Florida beggarweed (Desmodium tortuosum (sweet) DC.), nutsedge, and multiple broadleaf weed species control (Ducar et al. 2002). Traditional herbicide programs use as many as five or six herbicides applied at the full labeled rate. With the reduction of revenue due to the new Farm Bill, farmers will need new tactics to reduce their production cost possibly by configuring herbicide treatment combinations that will reduce the cost. The objective of this research was to determine the economic effectiveness of reduced cost (either by eliminating some herbicide treatments or reducing herbicide rates) herbicide programs. Materials and Methods Field studies were conducted in 2002 and 2003 at the West Florida Research and Education Center near Jay, FL, and in 2003 at the North Florida Research and Education Center near Marianna, FL, and at the Plant Science Research and Education Center near Citra, FL. Jay is located in the far West panhandle of Florida with soil type of Red Bay sand loam (fine-loamy, siliceous, thermic, Rhodic paleudults) at pH 5.8 and organic matter of 2.1%. Marianna is located in the central panhandle with Chipola loamy sand (loamy, siliceous, thermic Arenic Hapudult) soil type containing 1.0% organic matter and pH of 6.2. Citra is located in North Central Florida with soil type Sparr sand (loamy, siliceous, hyperthermic, Grossa-renic paleudult) with organic matter 1% and pH of 6.4. Conventional tillage system consisting of a deep moldboard plowing, leveling disking and one field cultivation prior to planting was used to prepare the field for peanut planting.

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52 The peanut variety C-99R was planted on May 7, 2002 at Jay, FL and April 30, May 5 and May 13, 2003 at Citra, Jay, and Marianna, FL respectively. Peanuts were planted at a depth of 6 cm and seeding rate of 122 kg/ha. Row spacing was 91 cm single rows in 2002 and 2003 at all three locations. Plots at Citra were four row (3.0m) wide and 6.1 m long. Plots at Jay and Marianna were four row (3.0m) wide and (7.0m) long. A randomized complete block was utilized as the experimental design to arrange the herbicide treatments. Soil fertilization and liming practices were in accordance with test recommendations by the University of Florida Soil Testing Laboratory. Florida Cooperative Extension Service recommendations were followed for management of fungicide, insecticide, and irrigation. Herbicide treatments and application rates are listed in tables 3.1 and 3.2 and consist of 9 commonly used herbicides in peanut production applied in various programs ranging in cost from $5 to $66 per hectare (Table 3.9, 3.10). All AC, early post (EPOST), or POST applications also included a non-ionic surfactant (Induce) of 0.25 % V/V. Herbicides were applied with a CO2 pressurized backpack sprayer calibrated to deliver 187 L/ha. Weed control was visually evaluated using a scale of 0 (no control) to 100 (complete control) early, ~35 days after planting (DAP), and late, ~120 DAP, during the growing season. The center two rows from each plot were harvested using conventional equipment approximately 140-148 DAP at physiological maturity as determined by the hull scrape method (Johnson 1987). Plot yields were converted to yield per hectare at 8% moisture.

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53 Economic return was determined for each treatment based on yield per hectare utilizing the following formula: Yield/hectare @ $0.501 per kg $1358/ha (total production cost) herbicide cost/ha The price per ton and total production cost was based on the average Florida peanut grower as determined through conversation with University of Florida's Extension Agriculture Economist. Herbicide prices used in the analysis were obtained from several farm supply stores throughout Florida's peanut production region. SAS (1996) Proc GLM software was used to analyze the data. Data were subjected to analysis of variance to test treatment effects an interactions. Means were separated using Fisher's Protected LSD Test at the p<0.1 level. Results and Discussion Treatments in 2002 were different from 2003 and location interactions for all parameters measured prevented pooling of data. Therefore, data is presented separately for each location and year. Weed Control-2002 Predominant weeds at Jay in 2002 were common cocklebur (Xanthium strumarium L), sicklepod (Senna obtusifolia L.), Florida pusley (Richardia scabra L.), and yellow nutsedge (Cyperus esculentus L.). Pendimethalin PPI fb imazapic at 3/4x and 2,4-DB POST provided greater than 87% late season control over all weeds evaluated (Table 3.3). Using imazapic at 1/2x with pendimethalin and 2,4-DB provided comparable weed control for a treatment cost $10/ha less. Pendimethalin fb either imazapic at full rate or 2,4-DB provided greater than 80% control over all weeds evaluated. Metolachlor and paraquat used AC fb 2,4-DB (a treatment without imazapic) also provided greater than 84% control over all weeds in the study.

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54 Weed Control-2003 Predominant weeds at Jay in 2003 were Florida beggarweed (Desmodium tortuosum (Sw) DC.), smallflower morningglory (Jaquemontia tamnifolia (L.) Griseb), sicklepod, Florida pusley, and purple nutsedge (Cyperus rotundus L.). Metolachlor alone AC only provided control of Florida pusley (87%) and purple nutsedge (89%) (Table 3.4). When paraquat was added AC to metolachlor, control of all weeds evaluated as >75% and when 2,4-DB was included to this treatment, control provided was >92%. Treatment with chlorimuron applied 60 DAE and paraquat AC required one treatment of 2,4-DB POST to obtain weed control >83%. Providing weed control greater than 92% over all weeds evaluated late season were treatments including metolachlor and paraquat AC and pendimethalin PRE fb imazapic POST or diclosulam PRE and paraquat AC. All of these three treatments used 2,4-DB POST. Treatments that did not receive a POST application of imazapic or 2,4-DB provided inadequate weed control over all weeds evaluated. Predominant weeds at Citra in 2003 were Florida beggarweed, pigweed (Amaranthus spp.), tropical spiderwort (Commelina benghalensis L.), crowfootgrass (Dactyloctenium aegyptium L.), and purple nutsedge. Tropical spiderwort was controlled 83 to 99% by all treatments except pendimethalin PPI alone, mainly due to the low populations of approximately 2 to 4 plants/m2 (Table 3.5). Treatments that did not utilize pendimethalin PPI controlled crowfootgrass less than 79%. When crowfootgrass was not controlled, it dominated the plot, reduced populations of other species, and interfered with harvesting (Table 3.7). Herbicide treatments which included pendimethalin PPI fb imazapic at 1x or 3/4x POST, imazapic plus 2,4-DB POST, diclosulam PRE fb paraquat AC fb 2,4-DB POST, and diclosualm at 1/2x PRE fb imazapic at 1/2x POST provided

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55 greater than 92% control over all weeds evaluated. Purple nutsedge control was higher in treatments using diclosulam (92%) compared to treatments using flumioxazin (80%) when both herbicides were followed by the same POST application. Predominant weeds at Marianna were crowfootgrass, sicklepod, smallflower morningglory, yellow nutsedge, and tropic croton (Croton glandulosus L.). Sicklepod was present in low populations and sporadic throughout the location. Similar to Citra, treatments that did not utilize pendimethalin PPI provided less than 74% control of crowfootgrass (Table 3.6). Pendimethalin PPI fb imazapic plus 2,4-DB POST, diclosulam PRE fb paraquat AC, or diclosulam at 1/2x PRE fb imazapic at 1/2x POST provided greater than 89% control over all weeds evaluated. Treatments using pendimethalin PPI fb imazapic at 1/2x plus 2,4-DB POST provided greater than 94% control of all weeds except sicklepod (84%). Providing greater than 90% control of all weeds except yellow nutsedge (78%) the program using pendimethalin PPI fb diclosulam at 1/2x PRE fb paraquat AC fb 2,4-DB POST. Yellow nutsedge populations were high at Marianna and pendimethalin alone provided the poorest control. Control was higher in treatments using diclosulam at 1x (81%) compared to treatments using flumioxazin at 1x (68%) when both herbicides were followed by the same POST application. All other weeds evaluated were controlled greater than 88% by these treatments. Peanut Yield There were no significant differences among yield treatments at Jay in 2002. Yields were low and variable across the study site (Table 3.7). This was likely due to a combination of a late-season infestation of Cylindrocladium black rot (CBR) and heavy rains from a tropical storm that delayed drying and harvesting after digging and inverting was complete. Treatments of metolachlor and pendimethalin application alone ant the

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56 non-treated check yielded the least. Highest yielding were metolachlor and paraquat AC, paraquat and 2,4-DB AC fb chlorimuron and 2,4-DB 60 DAE, and pendimethalin PPI fb diclosulam at 1/2x fb paraquat AC fb 2,4-DB POST (1943, 1923, and 2079 kg/ha, respectively). Sicklepod was the only weed that was controlled <83 % in these treatments. There was no significant difference among treatments at Jay and Citra, FL in 2003. At Jay, pendimethalin PPI fb imazapic POST was the highest yielding treatment (4609 kg/ha) (Table 3.8). Yielding the lowest was metolachlor applied AC alone (3505 kg/ha). At Citra, yield was generally higher and pendimethalin PPI fb imazapic and 2,4-DB POST was the highest yielding treatment (6616 kg/ha). Lower yield was observed with paraquat applied AC alone (2734 kg/ha). Crowfootgrass was an abundant weed at Citra and in treatments without pendimethalin yield was lower (2734, 3784, 3033 and 3613 kg/ha). At Marianna in 2003, treatments with pendimethalin PPI fb imazapic 1/2x POST, pendimethalin PPI fb imazapic 1/2x mixed with 2,4-DB POST, and pendimethalin PPI fb diclosulam 1/2x PRE fb paraquat AC, fb 2,4-DB POST were the highest yielding (4374, 4511, and 4394 kg/ha, respectively). Treatments using pendimethalin PPI fb paraquat AC and paraquat AC fb chlorimuron and 2,4-DB 60DAE, or fb 2,4-DB POST fb chlorimuron and 2,4-DB 60 DAE were the lowest yielding (2851, 2949, 2539 kg/ha, respectively). This was a result of the <37% control of crowfootgrass in the treatments without pendimethalin PPI. Pendimethalin fb paraquat was unable to adequately control smallflower morningglory and yellow nutsedge <79% resulting in lower yield.

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57 Economic Analysis Total revenue at Jay in 2002 were all negative values because of the low yield received per treatment. Treatment using pendimethalin PPI fb diclosulam at 1/2x PRE fb paraquat AC fb 2,4-DB POST provided the highest total revenue ($.63/ha) with treatment cost of $46.42/ha (Table 3.9 & 3.11). Jay in 2003 did show positive economic returns. Highest total revenue was obtained using pendimethalin PPI fb imazapic at 3/4x POST ($902.19/ha) with treatment cost of $49.38/ha (Table 3.10 and 3.12). Next highest return was realized from the program of pendimethalin PPI fb imazapic at 1x POST ($769.54/ha) costing $59.26/ha. Metolachlor applied PRE only was the lowest total revenue ($363.79/ha) with treatment cost of $14.00/ha. The highest total revenue at Citra was from the treatment pendimethalin PPI fb imazapic and 2,4-DB POST and next highest was from pendimethalin PPI fb imazapic at 1/2x ($1893.09 and $1673.72/ha) with treatment cost of $64.20 and $38.52/ha respectively. The lowest total revenue was earned with paraquat AC alone ($7.07/ha) at treatment cost of $2.00/ha. Highest total revenue at Marianna was achieved using pendimethalin PPI fb imazapic at 1/2x and 2,4-DB POST ($858.02/ha) with treatment cost of $44.44/ha. Next highest total revenue used pendimethalin PPI fb diclosulam at 1/2x PRE fb paraquat AC fb 2,4-DB POST ($797.41/ha) with treatment cost of $46.42/ha. Paraquat AC fb 2,4-DB POST fb chlorimuron and 2,4-DB 60DAE received the lowest total revenue ($-118.30/ha) due to grass control less than 37% with treatment cost of $13.20/ha. Results indicate that with regional standard herbicide treatments averaging $76/ha, adequate weed control and a net profit higher than the standard can be achieved with

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58 reduced cost herbicide treatments. Systems which used pendimethalin PPI followed by imazapic and/or 2,4-DB POST consistently, from the three locations, resulted in the highest total revenue earned costing less than the regional standard herbicide treatment. Since the passing of the 2002 Farm Bill, growers are now having to compete in a global market receiving the world price per ton for their peanut which is significantly lower than the price previously available. Peanut is a high management, high input crop with the cost of inputs steadily increasing. To remain competitive, growers must find ways in which to improve production efficiency. Using reduced cost combinations of herbicides applied without compromising yield and provide adequate weed control is one way to reduce the 40% of total production cost that results from pesticides (Aerts and Nesheim 2000).

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59 Table 3.1-2002 Reduced Cost Herbicide Treatments Abbreviation a Treatment b Rate Timing b g ai/ha Check NONTREATED Pen pendimethalin 1120 PRE Par paraquat 140 AC Par+ben paraquat + 140 + AC + bentazon 280 AC Pen+par pendimethalin fb 1120 + PRE fb paraquat 140 AC Pen+par+ben pendimethalin fb 1120 + PRE fb paraquat + bentazon 140 + 280 AC Met* metolachlor 1400 AC Met+par metolachlor + 1400 + AC + paraquat 140 AC Met+par* metolachlor + 1400 + AC + paraquat 140 AC Met+par+DB metolachlor + 1400 + AC + paraquat fb 140 + AC fb 2,4-DB 280 POST Par+chl paraquat fb 140 + AC fb chlorimuron 9 60 DAE Par+chl+DB paraquat fb 140 + AC fb 2,4-DB fb 280 + POST fb chlorimuron 9 60 DAE Par+2,4+chl+ paraquat fb 140 + AC fb DB 2,4-DB fb 280 + POST fb chlorimuron fb 9 + 60 DAE + 2,4-DB 280 60 DAE Pen+im Pendimethalin fb 1120 + PRE fb imazapic 70.6 POST Pen+im+DB pendimethalin fb 1120 + PRE fb imazapic + 70.6 + POST + 2,4-DB 280 POST

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60 Table 3.1 Continued Abbreviation a Treatment b Rate Timing b g ai/ha Pen+im3/4 pendimethalin fb 1120 + PRE fb imazapic 3/4x 46.6 POST Pen+im1/2 pendimethalin fb 1120 + PRE fb imazapic 1/2x 35.3 POST Pen+im3/4+ pendimethalin fb 1120 + PRE fb DB imazapic 3/4x + 46.6 + POST + 2,4-DB 280 POST Pen+im1/2+ pendimethalin fb 1120 + PRE fb DB imazapic 1/2x + 35.3 + POST + 2,4-DB 280 POST Pen+fl+par pendimethalin fb 1120 + PRE + flumioxazin fb 105.3 + PRE fb paraquat 140 AC Pen+fl+par+ pendimethalin fb 1120 + PRE + DB flumioxazin fb 105.3 + PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+fl1/2+ pendimethalin fb 1120+ PRE + Par+DB flumioxazin 1/2x fb 52.6+ PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+ds+par pendimethalin fb 1120+ PRE + diclosulam fb 26.8+ PRE fb paraquat 140 AC Pen+ds+par pendimethalin fb 1120+ PRE + +DB diclosulam fb 26.8+ PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+ds1/2+par pendimethalin fb 1120+ PRE + +DB diclosulam 1/2x fb 13.4 + PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST a Treatments did not include a surfactant. All other treatments received a surfactant of 0.25% V/V at AC, EPOST, POST, and 60DAE applications b + = tank mix, fb = followed by in a sequential treatment

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61 Table 3.2-2003 Reduce Cost Herbicide Treatments Abbreviation a Treatment b Rate Timing b g ai/ha Check NONTREATED Pen pendimethalin 1120 PRE Par paraquat 140 AC Par+ben paraquat + 140 + AC + bentazon 280 AC Pen+par pendimethalin fb 1120 + PRE fb paraquat 140 AC Pen+par+ben pendimethalin fb 1120 + PRE fb paraquat + bentazon 140 + 280 AC Met* metolachlor 1400 AC Met+par metolachlor + 1400 + AC + paraquat 140 AC Met+par+DB metolachlor + 1400 + AC + paraquat fb 140 AC fb 2,4-DB 280 POST Par+chl paraquat fb 140 + AC fb chlorimuron 9 60 DAE Par+chl+DB paraquat fb 140 + AC fb 2,4-DB fb 280 + POST fb chlorimuron 9 60 DAE Par+DB+chl+ paraquat fb 140 + AC fb DB 2,4-DB fb 280 + POST fb chlorimuron fb 9 + 60 DAE + 2,4-DB 280 60 DAE Pen+im Pendimethalin fb 1120 + PRE fb imazapic 70.6 POST Pen+im+DB pendimethalin fb 1120 + PRE fb imazapic 70.6 + POST + 2,4-DB 280 POST Pen+im3/4 pendimethalin fb 1120 + PRE fb imazapic 3/4x 46.6 POST Pen+im1/2 pendimethalin fb 1120 + PRE fb imazapic 1/2x 35.3 POST Pen+im3/4+ pendimethalin fb 1120 + PRE fb DB imazapic 3/4x + 46.6 + POST +

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62 Table 3.2 Continued Abbreviation a Treatment b Rate Timing b g ai/ha 2,4-DB 280 POST Pen+im1/2+ pendimethalin fb 1120 + PRE fb DB imazapic 1/2x + 35.3 + POST + 2,4-DB 280 POST Pen+fl+par pendimethalin fb 1120 + PRE + flumioxazin fb 105.3 + PRE fb paraquat 140 AC Pen+fl+par+ pendimethalin fb 1120 + PRE + DB flumioxazin fb 105.3 + PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+fl1/2+ pendimethalin fb 1120+ PRE + Par+DB flumioxazin 1/2x fb 52.6+ PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+ds+par pendimethalin fb 1120+ PRE + diclosulam fb 26.8+ PRE fb paraquat 140 AC Pen+ds+par pendimethalin fb 1120+ PRE + +DB diclosulam fb 26.8+ PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+ds1/2+par pendimethalin fb 1120+ PRE + +DB diclosulam 1/2x fb 13.4 + PRE fb paraquat fb 140+ AC fb 2,4-DB 280 POST Pen+fl1/2x+im1/2x pendimethalin + 1120 + PRE + flumioxazin 1/2x fb 52.6+ PRE fb imazapic 1/2x 35.3 POST Pen+ds1/2x+im1/2x pendimethalin + 1120+ PRE + diclosulam x fb 13.4 + PRE fb imazapic 1/2x 35.3 POST a Treatments did not include a surfactant. All other treatments received a surfactant of 0.25% V/V at AC, EPOST, POST, and 60DAE applications b + = tank mix, fb = followed by in a sequential treatment

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63 Table 3.3Weed control with reduced cost herbicide treatments in 2002 at Jay, FL. Late Season Treatment RCHSCa XANST CASOB CYPES -----------------------% Control----------------------------Pen 95 17 5 12 Par 72 92 55 52 Par+ ben 47 85 61 68 Pen+par 95 86 50 70 Pen+par+ben 95 93 58 72 Met* 90 20 0 47 Met+par 92 80 56 78 Met+par* 100 87 75 85 Met+par+DB* 97 91 84 92 Par+chl 37 85 62 77 Par+chl+DB 77 96 70 82 Par+DB+chl+ DB 87 95 68 87 Pen+im 100 97 80 97 Pen+im+DB 100 100 88 92 Pen+im3/4 100 92 76 96 Pen+im1/2 100 100 70 92 Pen+im3/4+ DB 100 100 87 97 Pen+im1/2+ DB 97 100 87 92 Pen+fl+par 95 95 56 50 Pen+fl+par+ DB 97 95 60 61 Pen+fl1/2+ Par+DB 97 95 59 41 Pen+ds+par 100 95 57 78 Pen+ds+par +DB 97 100 61 81 Pen+ds1/2+par +DB 100 100 67 83 LSD c 10 14.3 13.1 20.6 a XANST = (Xanthuim strumarium L), CASOB = (Senna obtusifolia), RCHSC = (Richardia scabra), and CYPES = (Cyperus esculentus) b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam c Fisher's Protected LSD test P < 0.1. Did not received a surfactant of 0.25% V/V. All other AC, POST & 60DAE treatments did

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64 Table 3.4Weed control with reduced cost herbicide treatments in 2003 at Jay, FL. Late Season a Treatment b CASOB IAQTA DEDTO RCHSC CYPRO -----------------------------------% control---------------------------------------Pen 42 62 83 79 73 Par 75 57 96 87 87 Par+ben 73 75 72 61 90 Pen+par 63 71 78 94 82 Pen+par+ben 83 87 94 96 88 Met 45 65 67 87 89 Met+par 77 75 92 93 94 Met+par+DB 94 99 99 99 92 Par+chl 94 67 96 79 84 Par+chl+DB 94 96 99 94 83 Par+DB+chl+ DB 86 99 99 99 89 Pen+im 89 99 99 99 99 Pen+im+DB 96 96 99 99 99 Pen+im3/4 79 99 91 99 99 Pen+im1/2 79 99 93 99 96 Pen+im3/4+ DB 84 99 87 99 99 Pen+im1/2+ DB 92 96 87 99 99 Pen+fl+par 77 88 86 96 91 Pen+fl+par+ DB 96 99 93 99 86 Pen+fl1/2+ Par+2,4 99 96 96 96 88 Pen+ds+par 74 99 89 99 96 Pen+ds+par+ DB 89 99 94 99 99 Pen+ds1/2+par +DB 95 99 94 99 92 Pen+fl1/2x+im1/2x 65 96 99 99 90 Pen+ds1/2x+im1/2x 73 99 99 99 99 LSD C 15 13 15 9 9 a DEDTO = Desmodium tortuosum, IAQTA = Jaquemontia tamnifolia, CASOB = Senna obtusifolia, RCHSC = Richardia scabra, and CYPRO = Cyperus rotundus b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam c Fisher's Protected LSD test P < 0.1.

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65 Table 3.5Weed control with reduced cost herbicide treatments in 2003 at Citra, FL Late Season a Treatment b DEDTO CYPRO AMASP DTTAE COMBA ------------------------------------% control---------------------------------------Pen 92 81 82 76 62 Par 74 77 71 50 94 Par+ben 78 90 74 47 94 Pen+par 95 90 96 92 96 Pen+par+ben 98 81 99 80 96 Met 88 86 89 37 89 Met+par 95 84 71 52 94 Met+par+DB 95 94 96 79 95 Par+chl 96 88 91 57 96 Par+chl+DB 98 91 88 42 94 Par+DB+chl+ DB 99 93 90 74 96 Pen+im 98 96 96 92 99 Pen+im+DB 98 99 99 99 96 Pen+im3/4 98 95 99 92 99 Pen+im1/2 83 96 95 99 84 Pen+im3/4+ DB 98 99 95 90 91 Pen+im1/2x+ DB 98 91 96 94 83 Pen+fl+par 98 82 99 86 95 Pen+fl+par+ DB 98 80 96 81 96 Pen+fl1/2+ Par+2,4 90 78 96 82 99 Pen+ds+par 98 93 96 89 95 Pen+ds+par+ DB 98 92 99 93 99 Pen+ds1/2+par +DB 98 92 96 86 95 Pen+fl1/2x+im1/2x 98 94 96 87 89 Pen+ds1/2x+im1/2x 98 96 96 92 99 LSD c 13.1 10.8 10.8 17.7 12.2 a DEDTO = Desmodium tortuosum, AMASP = Amaranthus spp., COMBA = Commelina banghalensis, DTTAE = Dactyloctenium aegyptium, and CYPRO = Cyperus rotundus b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam c Fisher's Protected LSD test P < 0.1.

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66 Table 3.6Weed control with reduced cost herbicide treatments in 2003 at Marianna, FL Late Season a Treatment b DTTAE CASOB IAQTA CYPES CVNGL ---------------------------% control----------------------------------------Pen 74 75 57 65 58 Par 35 80 45 86 85 Par+ben 42 77 52 83 83 Pen+par 99 91 56 69 84 Pen+par+ben 96 86 66 77 80 Met 84 89 73 80 72 Met+par 68 90 60 85 82 Met+par+DB 40 94 87 90 93 Par+chl 42 92 58 76 88 Par+chl+DB 35 90 78 88 95 Par+DB+chl +DB 37 92 89 88 91 Pen+im 99 91 99 98 77 Pen+im+DB 99 91 94 97 98 Pen+im3/4 99 83 88 94 77 Pen+im1/2 99 82 96 96 66 Pen+im3/4 +DB 99 81 84 87 88 Pen+im1/2x +DB 99 84 96 94 95 Pen+fl+par 99 99 81 72 96 Pen+fl+par +DB 93 96 96 65 99 Pen+fl1/2 +Par+2,4 96 94 92 67 95 Pen+ds+par 95 94 93 94 92 Pen+ds+par +DB 99 95 96 72 99 Pen+ds1/2+par +DB 99 90 96 78 99 Pen+fl1/2x+im1/2x 99 88 96 88 96 Pen+ds1/2x+im1/2x 99 89 99 99 96 LSDc 13.3 11.6 13.1 12.6 12.9 a DEDTO = Dactyloctenium aegyptium, CASOB = Senna obtusifolia, IAQTA = Jaquemontia tamnifolia, CYPES = Cyperus esculentus, and CVNGL = Croton glandulosus b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam c Fisher's Protected LSD test P < 0.1.

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67 Table 3.7-Yield with reduced cost herbicide treatments in 2002 at Jay, FL. Treatment a kg/ha Check 468 Pen 439 Par 1464 Par+ben 1494 Pen+par 1162 Pen+par+ben 1660 Met 615 Met+par 1631 Met+par 1943 Met+par+2,4 1699 Par+ch 1884 Par+chl+2,4 1660 Par+2,4+chl+2,4 1923 Pen+im 1465 Pen+im+2,4 1367 Pen+im3/4 1464 Pen+im1/2 1640 Pen+im3/4+2,4 1787 Pen+im1/2+2,4 1689 Pen+fl+par 1689 Pen+fl+par+2,4 1513 Pen+fl1/2+Par+2,4 1786 Pen+ds+par 1562 Pen+ds+par+2,4 1591 Pen+ds1/2+par+2,4 2079 LSD b NS a Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam b Fisher's Protected LSD test P < 0.1.

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68 Table 3.8Yield with reduced cost herbicide treatments in 2003 at Jay, Citra, and Marianna, FL Treatment a Jay Marianna Citra -------------------kg/ha---------------------------Check 3837 4023 3955 Pen 3769 3808 5713 Par 3866 4179 2734 Par+ben 4081 3496 4468 Pen+par 3954 2851 5664 Pen+par+ben 4023 3515 4126 Met 3505 3456 3784 Met+par 4160 3398 3003 Met+par+DB 3828 3359 3931 Par+chl 3867 3124 3906 Par+chl+DB 3611 2949 3613 Par+DB+chl+DB 4238 2539 4712 Pen+im 4364 3925 4077 Pen+im+DB 3681 3652 6616 Pen+im3/4 4609 3691 4980 Pen+im1/2 3964 4374 6127 Pen+im3/4+DB 4140 3886 4663 Pen+im1/2+DB 4296 4511 5615 Pen+fl+par 4042 3827 5151 Pen+fl+par+DB 4111 3378 4516 Pen+fl1/2+Par+DB 4081 3828 5029 Pen+ds+par 3974 3788 4077 Pen+ds+par+DB 4140 3554 5249 Pen+ds1/2+par+DB 4042 4394 5322 Pen+fl1/2x+im1/2x 3906 3710 4492 Pen+ds1/2x+im1/2x 3700 4160 5078 LSD b NS 934.3 NS a Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam b Fisher's Protected LSD test P < 0.1.

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69 Table 3.9Herbicide treatment cost for reduced cost study-2002 Treatment a $/hectare Check 0 Pen 15.80 Par 4.93 Par+ben 16.79 Pen+par 20.86 Pen+par+ben 32.59 Met 34.56 Met+par 39.5 Met+par 38.51 Met+par+DB 44.44 Par+ch 20.74 Par+chl+DB 26.66 Par+DB+chl+DB 32.59 Pen+im 59.25 Pen+im+DB 65.43 Pen+im3/4 48.64 Pen+im1/2 38.46 Pen+im3/4+DB 54.56 Pen+im1/2+DB 44.44 Pen+fl+par 50.86 Pen+fl+par+DB 56.79 Pen+fl1/2+Par+DB 41.97 Pen+ds+par 60.24 Pen+ds+par+DB 66.17 Pen+ds1/2+par+DB 46.41 a Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam

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70 Table 3.10Herbicide treatment cost for reduced cost study-2003 Treatment a $/hectare Check 0 Pen 15.80 Par 4.93 Par+ben 16.79 Pen+par 20.86 Pen+par+ben 32.59 Met 34.56 Met+par 39.5 Met+par+DB 44.44 Par+ch 20.74 Par+chl+DB 26.66 Par+DB+chl+DB 32.59 Pen+im 59.25 Pen+im+DB 65.43 Pen+im3/4 48.64 Pen+im1/2 38.46 Pen+im3/4+DB 54.56 Pen+im1/2+DB 44.44 Pen+fl+par 50.86 Pen+fl+par+DB 56.79 Pen+fl1/2+Par+DB 41.97 Pen+ds+par 60.24 Pen+ds+par+DB 66.17 Pen+ds1/2+par+DB 46.41 Pen+fl1/2x+im1/2x 53.58 Pen+ds1/2x+im1/2x 58.27 a Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam

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71 Table 3.11Total revenue for reduced cost treatments at Jay, FL Jay, FL Treatment b Revenuea ($/hectare) Check -1123.49 Pen -1153.82 Par -629.32 Par+ben -626.14 Pen+par -796.58 Pen+par+ben -558.76 Met -1084.39 Met+par -580.21 Met+par -422.81 Met+par+DB -551.07 Par+ch -434.66 Par+chl+DB -552.84 Par+DB+chl+DB -426.97 Pen+im -683.14 Pen+im+DB -738.42 Pen+im3/4 -673.03 Pen+im1/2 -574.66 Pen+im3/4+DB -517.10 Pen+im1/2+DB -556.08 Pen+fl+par -562.50 Pen+fl+par+DB -656.62 Pen+fl1/2+Par+DB -505.01 Pen+ds+par -635.52 Pen+ds+par+DB -626.92 Pen+ds1/2+par+DB -362.63 a Total revenue based on equation: yield per treatment at $0.501 per kg total production cost ($1358 per hectare) herbicide treatment cost per hectare. b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam

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72 Table 3.12Total revenue for reduced cost treatments Jay, FL Citra, FL Marianna, FL Treatment b Revenuea Revenue Revenue ($ hectare-1) Check 564.72 623.85 657.93 Pen 514.84 1588.98 534.39 Par 574.31 7.07 731.16 Par+ben 670.20 864.12 377.06 Pen+par 602.36 1459.24 49.65 Pen+par+ben 625.33 676.95 340.77 Met 363.76 503.59 339.23 Met+par 687.07 107.30 305.23 Met+par+DB 514.78 566.39 279.76 Par+ch 559.01 578.56 186.70 Par+chl+DB 424.31 425.31 92.58 Par+DB+chl+DB 733.07 970.59 -118.30 Pen+im 769.54 625.73 549.56 Pen+im+DB 422.35 1893.08 407.82 Pen+im3/4 902.19 1088.10 442.18 Pen+im1/2 589.84 1673.72 795.29 Pen+im3/4+DB 661.99 924.06 534.71 Pen+im1/2+DB 750.28 1411.23 858.02 Pen+fl+par 616.57 1172.30 508.85 Pen+fl+par+DB 645.23 848.18 277.93 Pen+fl1/2+Par+DB 645.01 1120.06 518.24 Pen+ds+par 573.12 624.74 479.92 Pen+ds+par+DB 650.38 1206.10 356.74 Pen+ds1/2+par+DB 621.03 1262.43 797.41 Pen+fl1/2x+im1/2x 545.72 839.36 447.50 Pen+ds1/2x+im1/2x 437.80 1128.31 668.30 a Total revenue based on equation: yield per treatment at $455 per ton total production cost ($550 per hectare) herbicide treatment cost per hectare. b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par=paraquat, fl=flumioxazin, ds=diclosulam

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CHAPTER 4 PEANUT (ARACHIS HYPOGAEA L.) VARIETY RESPONSE TO SELECTED HERBICIDES Introduction Differential response to herbicides is common in peanut (Jordan et al. 1998). These responses can include phytotoxic symptoms and/or a reduction in growth or yield. It is important to test new varieties they are released to determine tolerance to commonly used herbicides. Results from earlier studies show 'Early Bunch', a Virginia market type peanut, exhibited early-season injury from naptalam plus dinoseb and paraquat applied early post emergence (Brecke 1989). Imazapic injured 'Florunner', 'Georgia Runner', 'GK 7', 'NC 7', 'NC-V11', Southern Runner, 'Sunrunner', and Agra Tech VC-1' cultivars and reduced percentage of extra large and jumbo kernels in 'Florunner' and 'Sunrunner cultivars (Richburg el al. 1995). Research in Texas has shown at 14 DAT, diclosulam applied PRE at 18 and 27 g ai/ha injured Flavor Runner 458, Sunoleic 97R, TX 977006, and Georgia Hi O/L varieties 10-40% but did not injure the conventional variety 'Tamrun 96'. Injury continued 20 to 25% 42 DAT for the 'Flavor Runner 458' and 'Sunoleic 97R' varieties and 35 to 45% for the 'Georgia Hi O/L' from diclosulam applied PRE at 27 g ai/ha. In a 2000 test conducted in Florida where diclosulam was applied PPI at 0, 18, 27, or 54 g ai/ha to three runner market-type peanut cultivars, 'Georgia Green', 'C-99R', and 'MDR 98', peanut injury was not observed and canopy diameter was unaffected at any rate at any location in either year (Main et al. 2002). In 2000, diclosulam caused 73

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74 stunting, stand loss, and chlorosis to peanut when applied PPI and PRE. Therefore, a supplemental label was issued in 2001 for Texas and New Mexico changing preemergence application timing to no less than five days after planting through at-cracking at 26.8g ai/ha. The supplemental label for Oklahoma restricted diclosulam application to immediately after planting through at-cracking at no more than 20.1g ai/ha (Strongarm 2001). Flumioxazin was registered in 2001 and during its first year, injury was reported in Oklahoma, Georgia, North Carolina, and West Texas (Murphree et al. 2003). Early-season injury was a minor concern with flumioxazin when the herbicide was first introduced however in 2002 Main et al. observed some injury due to cool wet conditions in runner type varieties. Up to 25% flumioxazin injury was observed 14 and 28 DAT with the cultivars Georgia Green, C-99R, and MDR-98. Injury was still evident at 56 DAT but only with flumioxazin applied at 211 g/ha. In some cases, less than 5% injury 14 DAT was observed on all varieties from flumioxazin applied PRE at 105g ai/ha with all varieties tested (Murphree et al. 2002). Therefore, it is important to determine whether newer cultivars are tolerant to current herbicide application practices. In 2002, seven new peanut cultivars (AP-3, Carver, DP-1, GP-1, Hull, ANorden, UF00324) are in various stages of development and releases by Dr. D. W. Gorbet at the University of Florida. None of these cultivars have been evaluated for tolerance to herbicides. The objective of this study was to determine response of these new cultivars to commonly used herbicides in peanut production. Materials and Methods Field studies were conducted in 2003 at the West Florida Research and Education Center near Jay, FL and at the Plant Science Research and Education Center near Citra,

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75 FL. Jay is located in the far West panhandle of Florida with soil type of Red Bay sand loam (fine-loamy, siliceous, thermic, Rhodic paleudults) at pH 5.8 and organic matter of 2.1%. Citra is located in North Central Florida with soil type Sparr sand (loamy, siliceous, hyperthermic, Grossa-renic paleudult) with organic matter 1% and pH of 6.4. Conventional tillage system consisting of deep moldboard plowing, leveling disking and one field cultivation prior to planting was used to prepare the field for peanut planting. Pendamethalin was applied at 1.12kg ai/ha PPI to the entire test at all locations for control of small-seeded broadleaf and annual grasses. Peanuts were planted under conventional tillage at both locations. Seven recently released runner-type varieties, (AP-3, Carver, DP-1, GP-1, Hull, ANorden, UF00324), along with a standard variety (C-99R) were planted on May 8, 2003 at Jay, FL and May 15, 2003 at Citra, FL at a depth of 6 cm and seeding rate of 122 kg/ha. Peanuts were planted in 91cm single rows at both locations. Plots at Citra consisted of four rows, 3.0m wide and 6.1 m long. Plots at Jay consisted of four rows, 3.0m wide and 7.0m long. A split-plot design was utilized with four replications. The whole plot effect was peanut varieties and the sub plot effect was five herbicide treatment combinations. Soil fertilization and liming practices were in accordance with test recommendations by the University of Florida Soil Testing Laboratory. Florida Cooperative Extension Service recommendations were followed for management of fungicide, insecticide, and irrigation. Herbicide treatments and application rates listed in table 4.1 consist of five herbicide systems commonly used by peanut growers. Rates of the herbicides were two times that of the labeled rate in order to detect any differences in herbicide tolerance. All

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76 at cracking (AC), early post (EPOST), POST, or 60 days after emergence (DAE) treatments include a non-ionic surfactant (Induce) at 0.25 % V/V. Herbicides were applied with a CO2 pressurized backpack sprayer calibrated to deliver 187 L/ha. Plots were maintained weed-free throughout the growing season by cultivation and hand hoeing. Crop injury was visually evaluated two weeks after PRE application, one week after AC application, four weeks after EPOST application, and just prior to peanut harvest. Peanut canopy diameter was measured 1, 2 and 4 wk after AC application and 3 wk after 60 DAE application. Visual evaluations of injury were recorded on a scale of 0 to 100% with 0 = no injury and 100 = crop death. Canopy diameter measurements (cm) were recorded from 12 randomly selected plants from each plot and averaged. The center two rows from each plot were harvested with conventional equipment at physiological maturity for each variety as determined by the hull scrape method (Johnson 1987). Yields were adjusted to 8% moisture and converted to kilograms per hectare. SAS (1996) Proc Mixed software was used to analyze the data. Data were subjected to analysis of variance to test treatment effects and interactions. Means were separated using Fishers Protected LSD Test at the p<0.1 level. Results and Discussion There was an interaction between treatment and location for canopy and yield measurements, therefore, data will be presented by location. However, there was not a location interaction for injury measurements so data will be pooled over locations. Peanut Injury There was an interaction between peanut cultivar and herbicide treatment; therefore, data are presented for each cultivar and herbicide combination. Diclosulam caused 10-21% visual injury 2 wk after PRE application with ANorden and AP-3

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77 exhibiting the most significant damage (21%). Flumioxazin caused significant injury (75-48%) on all varieties evaluated 2 wk after PRE application. UF00324 injury was significantly the highest (75%) with DP-1, GP-1, and AP-3 displaying significantly lower injury (56, 50, 48%, respectively). When evaluated 1 wk after application of paraquat following diclosulam PRE, DP-1 exhibited the most injury (51%) while UF00324 showed the least damage (32%). All varieties recovered slowly by 7 wk after AC (15-23%), however, recovery was slowest for C-99R (23%). By 17 wk after AC recovery was complete for all varieties (<10%). Paraquat AC applied without a PRE application stunted Carver and 'C-99R' the most (35 and 36%, respectively) and Hull and GP-1 the least (26 and 25%, respectively) one week after treatment (Table 4.2). Seven weeks after AC application stunting was less for all varieties. At that time AP-3 and Hull recovered the slowest and exhibiting the most injury (26 and 25%) and GP-1 the least (11%). When evaluated 7 wk after application of paraquat AC following flumioxazin, injury was between 31 and 13% with ANorden and DP-1 displaying the most injury and GP-1 the least (31 and 13%, respectively). When evaluated 4 wk after imazapic EPOST application injury remained (37-26%) with AP-3 the most and DP-1 the least (37% and 26%, respectively). By 10 wk after EP, injury was less than 15% for all varieties. Peanut recovered (<15%) by the time of the last evaluation. When evaluated 5 wk after chlorimuron 60 DAE application, injury ranged from 5-21% stunting. Hull was significantly the least tolerant variety and ANorden significantly tolerated the most (21% and 5% injury, respectively).

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78 Canopy At Jay, there was not a significant main effect of variety or a variety by treatment interaction. Canopy means were averaged across all varieties for each treatment at each time of measurement and compared to treatment #5 the non-treated control (Table 4.3). All treatment canopy measurements were significantly different from the non-treated control at each time of measurement except for treatments using diclosulam PRE or flumioxazin PRE fb paraquat AC when measured at three weeks after the 60DAE application. This may be due to not receiving a treatment after the AC application. Diclosulam PRE fb paraquat provided the least reduction in canopy when compared to the control (79.6 and 79.8cm, respectively) late season and at each time of measurement. Paraquat AC fb chlorimuron 60 DAE caused the most reduction in canopy when compared to the control late season (73.0 and 79.8cm, respectively). At Citra, there was a significant main effect of variety (Table 4.4) and of herbicide treatment (Table 4.3). Canopy measurements for each variety were averaged over all treatments. DP-1 and Hull consistently had the lowest canopy at each time of measurement (Table 4.8). GP-1 and ANorden showed the highest level of tolerance to the herbicides the best resulting in significantly higher canopy diameter for most measurement timings at 3 wk after 60 DAE. UF00324 produced the largest canopy resulting in the highest canopy measurement followed by ANorden and GP-1 (89, 88.6 and 84.6cm, respectively). When canopy means were averaged over varieties for each treatment, results indicated significant differences when compared to the non-treated control (Table 4.3). Canopy size was significantly reduced for all treatments at all measurement times when compared to the non-treated control. Paraquat AC fb imazapic POST caused the most

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79 reduction in canopy size when compared to the control (78.1 and 88.1 cm, respectively) late season and at each time of measurement. Paraquat AC fb chlorimuron 60DAE resulted in the next highest canopy damage but only at the last measurement 3 wk after chlorimuron was applied. Later measurements indicate canopy recovery for the POST and 60DAE application treatments. Flumioxazin PRE fb paraquat AC resulted with less canopy damage at 1 wk after PRE and at last measurement when compared to diclosulam PRE fb paraquat AC (59.9, 55.5cm and 86.2 83.8 cm, respectively). Peanut Yield At Jay, there was a significant main effect of variety (Table 4.5) and of herbicide treatment (Table 4.6); however, there was not a variety by treatment interaction. Variety AP-3 was the lowest yielding (1894 kg/ha) and significantly lower than Carver and DP-1 (3195 and 3531 kg/ha, respectively), the highest yielding when averaged across all treatments. Yields of treatments using paraquat AC fb chlorimuron 60DAE, imazapic POST, or flumioxazin PRE at Jay, when averaged over all varieties, was significantly lower than the non-treated control which yielded highest. Flumioxazin PRE fb paraquat AC resulted in the lowest yield (2820 kg/ha) and next lowest was paraquat AC fb imazapic POST (2840 kg/ha). These yield reductions were most likely the result of the 2x rates used in this study to insure detection of any differences that exist among peanut cultivars. At Citra, there was an interaction between variety and treatment. Significant differences among many varieties were observed when each variety was compared to their non-treated control (Table 4.7). DP-1 was the only variety where yield for all four treatments was significantly lower than the non-treated (5810 kg/ha). Carver, GP-1, ANorden, and UF00324 were the varieties where yield for all four treatments were not

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80 significantly different from their non-treated check (5150, 4540, 4613, and 5199 kg/ha, respectively). This suggests that the four treatments had little to no effect on the yield of these four varieties when compared to the non-treated control. Treatment with paraquat AC fb imazapic POST consistently resulted in significantly lower yields compared to the non-treated control for the remaining varieties, AP-3, C-99R, and Hull (5712, 4467, 4078 kg/ha, respectively). Yield of C-99R was also reduced by the treatment using paraquat AC fb chlorimuron 60 DAE (4223 kg/ha). Canopy size and yield were significantly affected by the 2x rates of herbicides used in this study. At Citra, AP-3 exhibited some foliar damage, however, it provided the highest yield. DP-1 and Hull varieties displayed the most damage to canopy and were also the lowest yielding. When each varietys treatments were compared to the non-treated, DP-1 resulted in the greatest yield reduction. Paraquat AC fb imazapic POST resulted in significant yield reduction for AP-3, C-99R, DP-1, and Hull. At Jay, canopy damage was minimal and significant only up to 2 wk after EP for Carver and DP-1. AP-3, GP-1 and C-99R resulted in the lowest yield when averaged over all treatments possibly a result from the lowest yielding treatments of flumioxazin PRE fb paraquat AC and paraquat AC fb imazapic POST. Flumioxazin PRE fb paraquat AC resulted in the highest canopy reduction however recovered late season to become non-significant. Carver and UF00324 consistently had high yield at both locations with minimal canopy reduction. The results from these studies indicate that peanut varieties respond differently to commonly used herbicides. Therefore, it is important to determine whether newer

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81 cultivars are tolerant to current herbicide application practices. Among all treatments, GP-1 and Hull displayed the least visual injury when evaluated 1 to 4 wk after application. All varieties recovered late-season with <15% injury. However, when canopy measurements and yield was evaluated, results differed. Three varieties displayed the least canopy reduction and were the higher yielding. Carver, GP-1, and ANorden were not significantly affected by herbicide treatments when compared to their non-treated control. Yields ranged from 5614 to 2820 kg/ha with Carver yielding the highest. GP-1 is an early maturing variety with some TSWV resistance. ANorden and Carver are both medium maturity varieties with good tomato spotted wilt virus (TSWV) and disease resistance with higher yield than Georgia Green. ANorden yielded lower than Carver; however, it has better TSWV and disease resistance. Using ANorden may result in less usage of pesticides; however, the higher yield of Carver may make up for the increased use. Economic returns need to be analyzed to determine which variety results in higher total revenue.

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82 Table 4.1Variety tolerance herbicide treatments, Jay and Citra, FL. 2003 Abbreviation Treatment Rate Timing g ai/ha Par+chl Paraquat 140 AC fb Chlorimuron 9 60 DAE Ds+par Diclosulam 53.6 PRE fb Paraquat 140 AC Par+im Paraquat 140 AC fb Imazapic 70.6 EPOST Fl+par Flumioxazin 210.6 PRE fb Paraquat 140 AC Check Non-treated AC, EPOST, and 60DAE treatments received a surfactant at 0.25% V/V

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83 Table 4.2Percent injury as affected by treatments compared to non treated check for each variety at each measurement interval pooled over locations. Treatment Variety 2 wkPRE 1wkAC 4wkEP 5wk60DAE ---------------------------% injury------------------------------Par+chl C-99R 0 34 19 9 DP-1 0 30 18 14 GP-1 0 25 11 7 Hull 0 26 25 21 ANorden 0 30 17 5 Carver 0 35 15 9 AP-3 0 34 26 13 UF00324 0 27 16 9 LSD NS NS NS 6.6 Ds+par C-99R 17 45 23 3 DP-1 15 51 20 10 GP-1 10 37 15 5 Hull 16 33 18 2 ANorden 21 45 21 5 Carver 12 35 21 8 AP-3 21 33 20 5 UF00324 16 32 20 10 LSD 7.1 NS NS NS Par+im C-99R 0 36 30 8 DP-1 0 28 26 10 GP-1 0 33 26 12 Hull 0 27 33 15 ANorden 0 36 31 7 Carver 0 31 31 11 AP-3 0 25 37 6 UF00324 0 23 30 9 LSD NS 6.7 NS NS Fl+par C-99R 63 33 30 8 DP-1 56 32 31 10 GP-1 50 28 13 4 Hull 67 28 27 13 ANorden 71 33 31 15 Carver 68 30 28 12 AP-3 48 32 23 10 UF00324 75 30 23 7 LSDa 9.3 NS 10.5 NS a Fishers Protected LSD procedure @ P<0.1

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84 Table 4.3Canopy means for each treatment averaged over all varieties at Jay and Citra, FL. Treatment 1 Week EP 2 Weeks EP 4 Weeks EP 3 Weeks 60 DAE Jay, FL (cm) Par+chl 45.8* 62.3* 71.1* 73.0* Ds+par 47.7* 64.8* 71.6* 79.6 Par+im 38.3* 56.3* 67.9* 74.1* Fl+par 32.4* 50.8* 67.5* 76.8 Check 52.9 69.4 76.0 79.8 Citra, FL Par+chl 60.7* 71.0* 76.7* 80.4* Ds+par 55.5* 65.6* 77.5* 83.8* Par+im 50.2* 59.8* 71.1* 78.1* Fl+par 59.9* 70.1* 78.3* 86.2* Check 65.2 75.2 81.4 88.1 significance as compared to non-treated #5 at p< 0.1 level

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85 Table 4.4Canopy means for each variety averaged over treatments at Citra, Fl. Treatment1 1 Week EP 2 Weeks EP 4 Weeks EP 3 Weeks 60 DAE Citra, FL (cm) AP-3 58.9 69.2 72.8 78.7 C-99R 54.2 64.8 74.8 84 Carver 64.7* 75.2* 80.7 85.7 DP-1 47.5* 57.4* 68.7 75.9* GP-1 65.5* 74.5* 81.1 84.6 Hull 51.5 61.6 74 79.9 ANorden 65* 75* 83* 88.6 UF00324 59.5 69 80.9 89 *Canopy significantly different from conventional variety (C-99R) at p< 0.1 level

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86 Table 4.5 Yield of each variety averaged over all treatments at Jay, FL Variety Yield p value vs AP-3 kg/ha AP-3 1894 ---------C-99R 3116 0.076 Carver 3195 0.046* DP-1 3531 0.005* GP-1 2820 0.5005 Hull 3130 0.0705 ANorden 3101 0.0850 UF00324 3152 0.0610 *Significantly different form AP-3 variety a p< 0.1 level

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87 Table 4.6 Yield as affected by treatments averaged over all varieties at Jay, FL. Treatment Yield p value vs trt #5 kg/ha Par+chl 2882 0.0327* Ds+par 3138 0.7388 Par+im 2840 0.0155* Fl+par 2820 0.0104* Check 3283 --------* Yield significantly different form treatment #5 (control) at p< 0.1 level

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88 Table 4.7 Yield of each variety per treatment with significance compared to the non-treated control (check) Citra, FL Variety Treatment Yield VarietyTreatment Yield kg/ha kg/ha AP-3 Par+chl 6347 GP-1 Par+chl 4028 AP-3 Ds+par 6884 GP-1 Ds+par 4296 AP-3 Par+im 5712* GP-1 Par+im 4247 AP-3 Fl+par 6103 GP-1 Fl+par 4980 AP-3 Check 6933 GP-1 Check 4540 C-99R Par+chl 4223* Hull Par+chl 4638 C-99R Ds+par 5053 Hull Ds+par 4906 C-99R Par+im 4467* Hull Par+im 4078* C-99R Fl+par 5224 Hull Fl+par 5114 C-99R Check 5663 Hull Check 5199 Carver Par+chl 5614 ANorden Par+chl 4833 Carver Ds+par 5248 ANorden Ds+par 5150 Carver Par+im 5224 ANorden Par+im 4613 Carver Fl+par 5248 ANorden Fl+par 5150 Carver Check 5150 ANorden Check 4613 DP-1 Par+chl 4003* UF00324 Par+chl 4882 DP-1 Ds+par 4052* UF00324 Ds+par 4955 DP-1 Par+im 4174* UF00324 Par+im 4711 DP-1 Fl+par 4418* UF00324 Fl+par 5150 DP-1 Check 5810 UF00324 Check 5199 *Yield significantly different from non-treated control at p< 0.1 level

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CHAPTER 5 SUMMARY AND CONCLUSIONS These studies indicate reduced rates of diclosulam and flumioxazin, followed by imazapic can be used in Florida peanut production, provide adequate weed control without compromising yield and provide total revenue equal to or higher than the regional standard. Commonly used herbicides organized in combinations that are more cost efficient can control weeds without affecting yield and can also reduce the 40% of total production cost utilized for pesticides. With the release of seven new peanut varieties from the University of Florida, testing tolerance to commonly used herbicides is crucial to perform before applying reduced herbicide practices. The following summaries of these experiments could provide a foundation for peanut weed management on conventional and new peanut varieties utilizing reduce herbicide inputs therefore reducing cost and increasing total revenue. In 2002, weed management greater than 90% was achieved with diclosulam mixed with flumioxazin at x followed by imazapic at 2/3x at both Jay and Citra locations for common cocklebur, sicklepod, yellow nutsedge, pigweed, hairy indigo, and Florida beggarweed. In 2003, weed control at Jay was greater than 87% with all treatments for wild poinsettia and smallflower morningglory. Sicklepod control reached 85% only with full rates of diclosulam or flumioxazin fb imazapic or the regional standard. Florida beggarweed was not controlled >80% with diclosulam alone or when it was followed by imazapic at 1/4x or by imazapic alone. Flumioxazin at all rates provided the best Florida 89

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90 beggarweed control; however, purple nutsedge control greater than 80% required a sequential treatment of imazapic. Diclosulam at 1/2x alone and followed by imazapic at 1/4x provided greater than 85% control of purple nutsedge. Weed control at Citra was representative of an area with low weed pressure. The weed species with the highest density was tropical spiderwort and it may have reduced populations of other species. Greater than 80% control was observed with all treatments for purple nutsedge, sicklepod, hairy indigo, and cutleaf groundcherry. Florida beggarweed, similar to Jay, was not controlled with diclosulam alone or when it was followed by imazapic at 1/4x. Tropical spiderwort control was controlled by more treatments in twin row planting and required only diclosulam plus flumioxazin followed by imazapic at 1/4x to achieve 82% control. In single row planting, 1/2x rate of these three herbicides was required to obtain 86% control. All treatments resulted in peanut yield higher than the untreated check but there were no differences among the reduced rate treatments. When total revenue was calculated based on yield and cost per treatment, diclosulam plus flumioxazin followed by imazapic at 1/2x provided the highest total revenue earned for both locations. Reduced cost herbicide systems demonstrate they can provide weed control and higher total revenue when compared to the regional standard. Results in 2002 and 2003 at all locations had a similar trend. Pendimethalin was necessary to obtain grass control greater than 70% unless grass pressure was low then metolachlor provided adequate control. Metolachlor plus paraquat followed by 2,4-DB provided greater than 84% control of all weeds at Jay and cost only $38 per hectare, $20 less than the regional

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91 standard. Even though it provided good weed control, it was not one of the higher total revenue treatments. Treatments using pendimethalin followed by imazapic at 3/4x, pedimethalin followed by imazapic at 1/2x plus 2,4-DB, and pendimethalin followed by diclosulam PRE and paraquat AC followed by 2,4-DB provided greater than 80% weed control. At the Marianna site, pendimethalin PPI alone or fb diclosulam PRE then fb imazapic at 1/2x and/or mixed with 2,4-DB POST were the highest yielding herbicide program. Treatment costs were $9, $14, and $12/ha less and returned $60, $262, and $149/ha more than the regional standard. Studies conducted to evaluate herbicide tolerance in selected peanut cultivars indicate that certain peanut varieties are more tolerant than others and are affected differently depending on the herbicide systems. Yield and canopy were significantly affected by the higher than labeled rates of herbicides used in this study to insure detection of varietal differences. DP-1 and Hull displayed the greatest injury late season from paraquat AC fb chlorimuron at 2x. All varieties displayed 23-36% injury from paraquat AC alone. All varieties exhibited < 21% injury from diclosulam PRE with AP-3 and Norden displaying the most (21%). When paraquat was applied AC following diclosulam, injury increased for all varieties, some more than others. DP-1 was the most effected by paraquat with injury increasing from 15% to 51%. AP-3 displayed the least effect from paraquat only increasing injury form 21 to 33%. Flumioxazin PRE injured UF00324 and Norden (75, 71%) and imazapic injury was highest for AP-3 and Hull (37, 33%). All varieties recovered late season with injury < 15%. Variety canopy cover was

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92 not affected by cultivar at Jay, however, at Citra, DP-1 and Hull consistently had the smaller canopy size. Paraquat AC fb imazapic EPOST significantly reduced canopy for all varieties. Variety 'AP-3' was the lowest yielding and Carver and DP-1, the highest yielding, when averaged across all treatments at Jay. Yields following paraquat AC fb chlorimuron 60DAE, imazapic POST, or flumioxazin PRE, when averaged over all varieties, were significantly lower than the non-treated control which yielded highest. At Citra, DP-1 was the only variety where yield for all four treatments were significantly lower than the non-treated. Since the passing of the 2002 Farm Bill, growers are having to compete in a global market receiving the world price for their peanut which is significantly lower than the previous government supported price. Peanut are a high management, high input crop with the cost of inputs steadily increasing. To remain competitive, growers must find ways in which to improve production efficiency. Reducing the amount of herbicides applied is one way to reduce the 40% of total production cost that results from pesticides (Aerts and Nesheim 2000). Results from these studies indicate reduced rates of diclosulam and flumioxazin followed by imazapic can be used in Florida peanut production, provide adequate weed control without compromising yield and provide total revenue equal to or higher than the regional standard. With all the benefits of increased yield, increased grade, decreased tomato spotted wilt virus, and decreased weed populations proven in previous studies with twin-row planting regimes, the additional benefit of effectively using reduced rates of herbicides can only result in an increase in total revenue.

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93 Results indicate from these studies, that with regional standard herbicide treatments averaging $76/ha, adequate weed control and a net profit higher than the standard can be achieved with reduced cost herbicide treatments. Systems which used pendimethalin PPI followed by imazapic and/or 2,4-DB POST consistently, from the three locations, resulted in the highest total revenue earned costing less than the regional standard herbicide treatment. Three varieties displayed the least canopy reduction and were the higher yielding. Carver, GP-1, and ANorden were not significantly affected by herbicide treatments when compared to their non-treated control. ANorden yielded lower than Carver; however, it has better TSWV and disease resistance. Using ANorden may result in less usage of pesticides; however, the higher yield of Carver may make up for the increased use.

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APPENDIX A DAILY PRECIPITATION

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Table A-1. Daily precipitation (cm) for Citra, FL. May 2002 September 2002 May June July August September 1 0.00 0.00 0.05 0.51 0.18 2 0.00 0.00 0.00 0.43 0.05 3 0.00 0.00 0.00 0.36 0 4 0.00 0.00 0.05 0.03 0.3 5 0.00 0.00 1.98 0 0.2 6 0.00 0.00 0.00 0.00 0.00 7 0.00 0.00 0.00 0.05 0.00 8 0.00 0.00 0.3 0.00 0.00 9 0.00 0.00 0.13 0.00 0.00 10 0.00 0.00 0.38 0.00 0.00 11 0.00 0.00 0.00 0.00 0.00 12 0.00 0.00 0.25 2.62 3.26 13 0.00 0.00 0.38 1.17 0.23 14 0.00 0.00 0.00 0.00 2.87 15 0.00 0.00 0.00 0.97 0.23 16 0.00 0.00 0.00 0.05 3.66 17 0.00 0.3 0.48 0 0.46 18 0.00 0.61 0.00 2.05 0.36 19 0.00 0.58 0.00 0.00 0.00 20 0.00 0.86 2.57 0.03 0.00 21 0.00 0.41 0.43 0.00 0.00 22 0.00 5.28 0.2 0.81 0.00 23 0.00 1.04 0.08 0.03 0.00 24 0.00 1.91 0.00 0.00 0 25 0.00 1.19 0.97 0.00 0 26 0.00 0.79 0 0.05 0 27 0.00 0 1.63 0.2 0.00 28 0.00 0.23 0.03 0.86 0.00 29 0.00 0.38 0.69 0.1 0.00 30 0.00 0.03 0 2.64 0.00 31 0.00 0 1.37 Total 0 13.61 10.6 14.33 11.8 Normal 8.38 19.56 21.84 18.54 18.54 Difference -8.38 -5.95 -11.25 -3.22 -6.35 95

PAGE 105

96 Table A-2. Daily precipitation (cm) for Jay, FL. May 2002 September 2002 May June July August September 1 0.00 0.00 0.00 2.64 0.00 2 0.00 0.00 0.00 0.00 0.00 3 0.00 0.00 0.36 0.00 0.00 4 0.00 0.43 0.1 0.03 0.00 5 0.00 0.00 0.00 0.00 0.00 6 0.00 0.05 0.03 0.00 0.79 7 0.00 0.18 1.6 0.00 0.00 8 0.00 1.5 2.11 0.00 0.00 9 0.00 0.00 0.66 0.00 0.00 10 0.00 0.05 0.00 0.00 0.00 11 0.00 0.00 0.00 0.00 0.00 12 0.00 0.00 0.00 0.18 5.38 13 0.18 0.00 0.53 0.05 3.89 14 0.00 0.36 0.69 0.00 5.36 15 0.00 0.00 0.03 0.00 1.19 16 0.00 0.00 0.00 0.00 0.00 17 0.00 0.00 0.00 0.00 0.00 18 2.87 0.03 0.00 0.97 0.00 19 1.19 0.00 0.00 2.69 0.00 20 0.00 0.03 0.53 0.00 0.00 21 0.00 0.08 0.00 0.00 0.40 22 0.00 0.00 0.99 0.00 0.07 23 4 0.51 1.5 0.00 0.00 24 0.00 0.74 1.6 0.00 3.22 25 0.00 0.08 0.03 2.03 16.38 26 0.00 3.48 0.28 0.00 6.75 27 0.00 0.23 0.23 1.5 0.00 28 0.00 0.00 4.5 0.08 0.00 29 0.00 0.00 0.43 0.03 0.00 30 0.2 0.18 0.15 0.00 0.88 31 0.00 0.00 0.00 0.1 0.00 Total 8.73 7.9 16.33 10.29 44.31 Normal 10.41 14.22 17.53 15.27 12.45 Difference -1.68 -6.32 -1.2 -4.92 31.86

PAGE 106

97 Table A-3. Daily precipitation (cm) for Jay, FL. May 2003 September 2003 May June July August September 1 0.08 0.00 3.48 1.47 0.00 2 0.61 0.53 0.13 0.00 0.00 3 1.37 2.69 0.03 0.00 0.00 4 0.00 0.00 0.38 1.70 0.00 5 0.00 1.47 1.22 0.00 0.00 6 0.00 8.64 0.00 1.02 4.06 7 0.00 0.97 0.05 2.57 0.00 8 0.00 1.83 0.00 0.00 0.00 9 0.00 0.00 0.00 0.00 0.00 10 0.00 0.00 0.00 0.00 0.00 11 0.76 0.10 1.73 0.00 0.00 12 0.00 4.34 0.03 0.79 0.00 13 0.00 1.45 0.00 1.07 5.26 14 0.00 0.15 0.00 0.00 0.28 15 0.53 0.56 0.00 0.00 0.00 16 0.00 0.05 0.00 7.16 0.00 17 0.00 0.81 0.00 0.00 0.00 18 6.76 3.23 0.00 0.03 0.00 19 0.00 0.10 0.00 0.00 0.00 20 3.23 0.76 0.00 0.53 0.00 21 0.13 0.10 0.00 0.13 0.30 22 0.08 1.47 0.00 0.00 3.07 23 0.00 0.28 0.76 0.94 0.00 24 0.00 0.10 0.00 0.00 0.00 25 0.00 0.00 0.10 0.03 0.00 26 0.41 0.00 0.10 0.03 0.00 27 0.03 0.00 0.00 0.00 0.00 28 0.00 0.00 0.53 0.20 0.00 29 0.00 3.00 0.99 5.82 0.00 30 0.00 10.36 0.00 1.04 0.00 31 0.00 1.93 0.00 Total 13.97 43.00 11.46 24.51 12.98

PAGE 107

REFERENCES Aerts, M. J. and O. N. Nesheim. 2000. Florida Crop/Pest Management Profiles: Peanuts. Univ. of Florida Coop. Ext. Serv. PI044. Baldwin, J. A., J. P. Beasley Jr, S. L. Brown, J. W. Todd, and A. K. Culbreath. 1998. Yield, grade, and tomato spotted wilt virus incidence of four peanut cultivars in response to twin versus single row planting patterns. Proc. Am. Peanut Res. and Educ. Soc. Inc. 30:51. Baldwin, J. A., D. E. McGriff, T. B. Tankersley, A. S. Luke, and S. M. Fletcher. 2000. Effect of seeding rate on yield and grade of Georgia Green peanut when planted in twin row patterns. Proc. Am. Peanut Res. and Educ. Soc. Inc. 32:44. Baldwin, J. A., R. McDaniel, D. E. McGriff, T. B. Tankersley. 2001. Yield, grade, and tomato spotted wilt virus incidence of Georgia Green and AT-201 peanut when planted in twin versus single row pattern. Proc. Am. Peanut Res. and Educ. Soc. Inc. 33:31. Baughman, T. A., W. J. Gricher, P. A. Dotray, and J. C. Reed. 2003. Weed control with reduced rates of Cadre and Pursuit in peanut. Proc. South. Weed Sci. Soc. 56:35. Beasley Jr, J. P., and J. A. Baldwin, 1992. Row pattern demonstrations in Georgia. Proc. Am. Peanut Res. and Educ. Soc. Inc. 24:32 Besler, B. A., W. J. Grichar, and K. D. Brewer. 2002. Response of full and reduce rates of imazapic and diclosulam for yellow nutsedge control when peanuts are grown in a conventional vs twin row configuration. Proc. Am. Peanut Res. and Educ. Soc. Inc. 34:89. Brecke, B. J. 1989. Response of peanut cultivars to selected herbicide treatments. Proc. South, Weed Sci. Soc. 42:28. Cadre 2001 product label. American Cyanamid Company. Cardina, J., A. C. Mixon, and G. R. Wehtje. 1986. Reduce cost weed control systems for Sunbelt Runner peanuts. Proc. Am. Peanut Res. and Educ. Soc. Inc. 18:46. Colvin, D. L., R. H. Walker, M. G. Patterson, G. Wehtje, and J. McGuire. 1985. Row pattern and weed management effects on peanut production. Peanut Sci. 12:22-27. 98

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99 Cranmer, J. R., J. V. Altom, J. C. Braun, and J. A. Pawlak. 2000. Valor Herbicide: A new herbicide for weed control in cotton, peanuts, soybeans, and sugarcane. Proc. South. Weed Sci. Soc. 53:158. Dotray, P. A., J. W. Keeling, W. J. Grichar, T. A. Baughman, R. G. Lemon, and S. A. Senseman. 2002. Cotton response to imazapic and imazethapyr. Proc. South. Weed Sci. Soc. 55:168. Ducar, J. T., B. J. Brecke, G. E. MacDonald. 2002. Weeds in the Sunshine: Weed management in peanuts 2002. Univ. of Florida Coop. Ext. Serv. SS-AGR-03. Gerngross, C. A., S. A. Senseman. 2002. Diclosulam persistence in soil and its effect on peanut rotational crops. South. Weed Sci. Soc. 55:149. Gorbet, D. W., T. Stadsklev, K. Jordan. 2002. New release: Andru II, Carver, DP-1, GP1, Norden. Florida Foundation Seed Prod. Pub # 02-P1, P2, P3, P4, P6. Hauser, E. W., G. A. Buchanan, A. Gale, R. L. Nichols, and R. M. Patterson. 1982. Effects of Florida beggarweed (Desmodium tortuosum) and sickelpod (Cassia obtusifolia) on peanut(Arachis hypogaea) yield. Weed Science. 30:602-604. Heap, I. International Survey of Herbicide Resistance Weeds. 2001. Online, http://www.weedscience.com January 10, 2004. Johnson, W.C., III. 1987. The hull scrape method to assess peanut maturity. Georgia Coop. Ext. Serv. Bull. 958. Jordan, D. L., A. S. Culpepper, R. B. Batts, and A. C. York. 1998. Response of Virginia type peanuts to norflurazon. Peanut Sci. 25:4-7 Lanier, J. E., D. L. Jordan, P. D. Johnson, J. F. Spears, and R. Wells. 2003. Weed management in peanut planted in various row patterns. Proc. South. Weed Sci. Soc. 56:33. Main, C. L., J. Treadway Ducar, and G. E. MacDonald. 2002. Response of three runnertype peanut cultivars to diclosulam. Weed Technol. 16:593-596. Main, C. L., J. Treadway Ducar, E. Ben Whitty, and G. E. MacDonald. 2003. Response of three runner-type peanut cultivars to flumioxazin. Weed Technol. 17:89-93. Mozingo, R. W., and C. W. Swann. 2000. Response of VA 98-R peanut to twin vs single row planting patterns. Am. Peanut Res. and Educ. Soc. Inc. 32:43. Murphree, T. A., P. A. Dotray, J. W. Keeling, B. L. Porter, T. A. Baughman, W. J. Grichar, and R. G. Lemon. 2002. Varietal tolerance to diclosulam and flumioxazin in Texas peanut. Proc. South. Weed Sci Soc. 55:33.

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100 Murphree, T. A., P. A. Dotray, J. W. Keeling, T. A. Baughman, W. J. Grichar. 2003. Response of five peanut varieties to diclosulam and flumioxazin in Texas peanut. Proc. South. Weed Sci. Soc. 56:34 Parham, S. A. 1942. Peanut production in the Costal Plain of Georgia. Georgia Costal Plain Exp. Stn. Bull. 34. Prostko, E. P., T. L. Grey. 2004. A comparison of full and reduce rate weed management programs in peanut. Proc. South. Weed Sci. Soc. 57:35 Richburg, J. S., J. W. Wilcut, A. K. Culbreath, and C. K. Kevien. 1995. Response of eight peanut (Arachis hypogaea L.) cultivars to the herbicide AC 263,222. Peanut Sci. 22:76-80. Smith, N., 2003. Estimated cost and returns for peanut under the 2002 Farm Bill. 2003 Peanut Update. Univ. of Georgia Coop. Ext. Serv. Strongarm 2001 Supplemental Labeling. Dow Agrosciences. Swann, C. W. 2000. Weed management in peanut with diclosulam and imazapic. South. Weed Sci. Soc. 53:35. Troxler, S. C., J. A. Tredaway, D. L. Jordan, B. J. Brecke, S. D. Askew, and J. W. Wilcut. 2001. Weed management in peanuts with reduce rates of diclosulam, flumioxazin, and imazapic. South. Weed Sci. Soc. 54:36. United States Department of Agriculture Agriculture Statistics. "On-line database. 2002. http://www.usda.mannlib.cornell.edu/reports/nassr/field December 10, 2003. Valor 2001 product label. Valent USA Corp. Vencill, W. K., 2002. Herbicide Handbook. 8th Ed. Weed Sci. Soc. of Amer. Lawrence, KS. 139 & 249 p. Veneman, A. M. and F. A. Vogel. 2001. Acreage: Crop Production Report. National Agricultural Statistics Service, Agricultural statistics Board, U. S. Dept of Agri. Cr Pr 2-5 (6-01). Web page: http://usda.mannlib.cornell.edu/reports/nassr/field December 10, 2003 Walsh, M. J., R. D. Duane, and S. B. Powles. 2001. High frequency of chlorsulfuronresistant wild radish (Raphanus raphanistrum L.) populations across the Western Australian wheatbelt. Weed Tech. 15:199-203 Walsh, M. J., S. B. Powles, B. R. Beard, B. T. Parkin, S. A. Porter. 2004. Multipleherbicide resistanceacross four modes of action in wild radish (Raphanus raphanistrum L.). Weed Sci. 52:8-13.

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101 Webster, T. M., 2001. Weed Survey-Southern States. Ten most troublesome weeds. South. Weed Sci. Soc. 54:249. South. Weed Sci. Soc. 54:36. Wehtje, G., R. H. Walker, M. G. Patterson, J. A. McGuire. 1984. Influence of twin rows on yield and weed control in peanuts. Peanut Sci. 11:88-91. Wilcut, J. W., S. D. Askew, W. A. Bailey, J. F. Spears, and T. G. Isleib. 2001. Virgina market-type peanut (Arachis hypogaea L.) cultivar tolerance and yield response to flumioxazin preemergence. Weed Technol. 15:137-140. Wright, D. L., J. J. Marois, J. R. Rich, R. K. Sprenkel, and E. B. Whitty. 2001. Conservation tillage peanut production. Univ. of Florida Coop. Ext. Serv.AG187.

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BIOGRAPHICAL SKETCH Samuel D. Willingham was born May 29, 1974, in Newberry, FL. He attended Santa Fe High School and graduated May 1992. After graduation, he attended Santa Fe Community College and worked full-time at a financial institution. Once graduating in 1999 he entered the University of Florida in August and received a Bachelor of Science in agronomy specializing in crop production and management with a minor in agribusiness on May 2002. Upon graduation, he was accepted into the graduate program at the University of Florida, pursuing a Master of Science degree in agronomy with a concentration in weed science under the supervision of Dr. Barry Brecke. Sam has presented at the Weed Science Society of America, the Southern Weed Science Society, the Florida Weed Science Society, the Deep South Weed Tour, the IFAS College of Agriculture and Life Sciences Graduate Research Symposium, and the Peanut Field Day at the North Florida Research and Education Center. Following completion of his Master of Science degree, he plans to attend Texas A&M University to pursue a Doctor of Philosophy degree. 102


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Title: Reduced Herbicide Inputs for Weed Management in Florida Peanut (Arachis hypogaea L.) Production
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Copyright Date: 2008

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Holding Location: University of Florida
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Permanent Link: http://ufdc.ufl.edu/UFE0005160/00001

Material Information

Title: Reduced Herbicide Inputs for Weed Management in Florida Peanut (Arachis hypogaea L.) Production
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
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REDUCED HERBICIDE INPUTS FOR WEED MANAGEMENT IN FLORIDA
PEANUT (Arachis hypogaea L.) PRODUCTION
















By
SAMUEL D. WILLINGHAM


















A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2004















ACKNOWLEDGMENTS

For their support and guidance at the University of Florida, I wish to express

sincere appreciation to my graduate committee: Dr. Barry Brecke, Dr. Greg MacDonald,

Dr. Joyce Tredaway Ducar, and Dr. Ben Whitty.

I would like to acknowledge Nick Pool, Melissa Barron, Amanda Collins, and

Nasir Shaik. While their assistance helped make this research possible, their fellowship

and camaraderie also made my time at the University of Florida enjoyable.
















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S .................................................................................................. ii

LIST OF TABLES.. .. ....... ......... ................... .................v

ABSTRACT.................. .................. vii

CHAPTER

1 INTRODUCTION ................... .................. .............. .... ......... .......

Current M anagem ent Strategies ............................................. ...............2
Diclosulam Flum ioxazin, and Im azapic ............................................. .......4
Reduced Rate H erbicide Research................................ ................6
Row Spacing Research ............................................... .... .....7
N ew P eanu t V varieties ............................................................................................ 10
Summary...................................... .................. ............... .........14

2 EFFECTS OF REDUCED APPLICATIONS OF DICLOSULAM, FLUMIOXAZIN,
AND IMAZAPIC ON WEED MANAGEMENT IN PEANUT (Arachis hypogaea
L .) PR OD U CTION ........ .. ..... .. .. ...... ........... .............. 16

Introduction ................................. ..... ...........16
M materials an d M eth o d s .......................................................................................... 18
Results and Discussion ............................................... ........21
W eed Control-2002 ..................... ................................21
W eed Control-2003 ..................... .......... .............. .. 22
Peanut Yield ................................................24
Economic Analysis ................ ...........................25

3 EFFECTS OF REDUCED COST HERBICIDE TREATMENT COMBINATIONS
ON WEED MANAGEMENT IN PEANUT (Arachis hypogaea L.)
PRODUCTION.......... ...... .................... .....................49

Introduction........... ........... ............ .. ...... ................49
M materials an d M eth o d s .......................................................................................... 5 1
Results and Discussion ........................ ................. .......... 53
W eed Control-2002 ..................... .......... .......... ..... 53
W eed Control-2003 ..................... ................................54










Peanut Y field ....................................................... 55
E conom ic A naly sis .................. .................. .................. ......... ............... 57

4 PEANUT (Arachis hypogaea L.) VARIETY RESPONSE TO SELECTED
HERBICIDES .......................... .....................73

Introduction.............................. ..................73
M materials and M methods ............................................................74
Results and Discussion ............................................... .......... 76
Peanut Injury ......................................... .........76
Canopy ........................... ............ ..........78
Peanut Yield ...................................................... ........79

5 SUMMARY AND CONCLUSIONS.......................................................... 89

APPENDIX DAILY PRECIPITATION............................ .......... 94

REFERENCES ...................... ............................... 98

BIOGRAPHICAL SKETCH .............. ..............................102
















LIST OF TABLES


Table page

2.1 2002 Reduced rate treatments-Jay and Citra, FL................................................27

2.2 2002 Reduced rate treatments-Marianna, FL............ ................... 28

2.3 2003 Reduced rate treatments-Jay and Citra, FL. ..................................... 29

2.4 Weed control as affected by reduced rate herbicide treatments in 2002 at
Jay, FL....................... ................ ........ .3 1

2.5 Weed control as affected by reduced rate herbicide treatments in 2002 at
Citra, FL........................ ............... .......... 32

2.6 Weed control as affected by reduced rate herbicide treatments in 2002 at
Marianna, FL..............................................33

2.7 Weed control as affected by reduced rate herbicide treatments in 2003 at
Citra, FL in single row study ......................................................... 34

2.8 Weed control as affected by reduced rate herbicide treatments in 2003 at
C itra, FL in tw in row study ........................................................................ ...........36

2.9 Weed control as affected by reduced rate herbicide treatments in 2003 at
Jay, FL in single row study ........................................................................ ... ...... 38

2.10 Weed control as affected by reduced rate herbicide treatments in 2003 at
Jay, FL in tw in row study .............................................. ............... 40

2.11 Peanut yield as affected by reduced herbicide treatments in 2002 at Jay and
Citra, FL ........................... ............................42

2.12 Peanut yield as affected by reduced herbicide treatments in 2002 at Marianna,
FL........................................................ ........ 43

2.13 Peanut yield as affected by reduced rate herbicide treatments in 2003 at Jay
and Citra, Fl. in twin and single row studies............................... ........... ....44

2.14 Total revenue per treatment as affected by yield and treatment cost separated
by location and row spacing-2003 ............................. ............... 46









2.15 Herbicide treatment cost for reduced rate study-2003 .......................................48

3.1 2002 Reduced Cost Herbicide Treatments ................. ................. ............59

3.2 2003 Reduce Cost Herbicide Treatments .................................... ....61

3.3 Weed control with reduced cost herbicide treatments in 2002 at Jay, FL.............63

3.4 Weed control with reduced cost herbicide treatments in 2003 at Jay, FL.............64

3.5 Weed control with reduced cost herbicide treatments in 2003 at Citra, FL ..........65

3.6 Weed control with reduced cost herbicide treatments in 2003 at Marianna, FL ...66

3.7 Yield with reduced cost herbicide treatments in 2002 at Jay, FL.......................67

3.8 Yield with reduced cost herbicide treatments in 2003 at Jay, Citra, and
Marianna, FL..............................................68

3.9 Herbicide treatment cost for reduced cost study-2002 .......................................69

3.10 Herbicide treatment cost for reduced cost study-2003 .......................................70

3.11 Total revenue for reduced cost treatments at Jay, FL-2002...............................71

3.12 Total revenue for reduced cost treatments-2003 ...................................... 72

4.1 Variety tolerance herbicide treatments, Jay and Citra, FL. 2003...........................82

4.2 Percent injury as affected by treatments compared to non treated check for
each variety at each measurement interval pooled over locations......................83

4.3 Canopy means for each treatment averaged over all varieties at Jay and Citra,
FL................................................................ 84

4.4 Canopy means for each variety averaged over treatments at Citra, Fl. .................85

4.5 Yield of each variety averaged over all treatments at Jay, FL........................ 86

4.6 Yield as affected by treatments averaged over all varieties at Jay, FL...............87

4.7 Yield of each variety per treatment with significance compared to the
non-treated control (check) ............................................................. .............88

A. 1 Daily precipitation (cm) for Citra, FL. May 2002 September 2002....................95

A.2 Daily precipitation (cm) for Jay, FL. May 2002 September 2002 ...................96

A.3 Daily precipitation (cm) for Jay, FL. May 2003 September 2003 ...................97
















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

REDUCED HERBICIDE INPUTS FOR WEED MANAGEMENT IN FLORIDA
PEANUT (Arachis hypogaea L.) PRODUCTION

By

Samuel D. Willingham

May 2004

Chair: Barry J. Brecke
Cochair: Greg MacDonald
Major Department: Agronomy

Field studies were conducted in 2002 and 2003 at Citra, Jay, and Marianna, FL, to

evaluate the effects of reduced herbicide inputs on weed management and yield in peanut

in both twin-and single-row spacing regimes. Economic return was also calculated to

determine the return to management for all herbicide systems. Seven peanut varieties

recently released by the University of Florida in 2002 were evaluated to determine

tolerance to five commonly used herbicide systems.

At Jay and Citra in 2002, diclosulam plus flumioxazin applied preemeregence

(PRE) at 1/4x (1/4 labeled use rate) followed by imazapic post emergence (POST)at 1/2 or

2/3x was the lowest herbicide input that provided greater than 85% control of common

cocklebur (Xanthium strumaruim L.), sicklepod (Senna obtusifolia L.), and yellow

nutsedge (Cyperus esculentus L.) and greater than 90% control of pigweed (Amaranthus

spp), hairy indigo (Indigofera hirsuta L.), and Florida beggarweed (Desmodium

tortuosum sw. DC).









At Citra in 2003, the twin row pattern provided greater overall control of tropical

spiderwort (Commelina banghalensis L.) than the single row pattern (75 and 65%,

respectively). Diclosulam applied with flumioxazin PRE followed by (fb) imazapic

POST both at 14x for twin and at 1/2x for single rows was the lowest input that provided

greater than 82% control. Sicklepod required Ix treatments for > 85% control and

Florida beggarweed control was > 85% except with diclosulam alone or fb imaxapic at

1/4x. Diclosulam controlled purple nutsedge 10 to 20% greater than flumioxazin. Total

revenue at Citra and Jay was highest for diclosulam applied with flumioxazin followed

by imazapic, all at 1/2x ($1981.68 and $986.00/ha, respectively).

In the reduced cost studies at Jay in 2002 and 2003, and at Citra and Marianna in

2003, the greatest level of weed management was observed with pendimethalin pre plant

incorporated (PPI), fb imazapic and/or 2,4-DB POST. At Marianna, treatments with

pendimethalin PPI alone or fb diclosulam PRE fb imazapic 1/2x and/or mixed with 2,4-

DB POST were the highest yielding at 4374, 4511, and 4394 kg/ha, respectively,

resulting in the highest total revenue.

'C-99R' and 'Hull' displayed the greatest injury late-season from paraquat at-

cracking (AC) fb chlorimuron at 2x. All varieties exhibited 25-35% injury from paraquat

AC Ix alone. Varieties exhibited < 21% injury from diclosulam PRE. Flumioxazin PRE

injured 'UF00324' (75%) and 'Norden' (71%), and imazapic injury was highest for 'AP-

3' (38%) and 'Hull' (33%). All varieties recovered by late season. At Citra, 'DP-1' and

'Hull' consistently had smaller canopy over all treatments. Paraquat AC fb imazapic

EPOST significantly reduced canopy size for all varieties. Variety AP-3 was the lowest

yielding and significantly lower than 'Carver' while 'DP-1' was the highest yielding









when averaged across all treatments at Jay. At Citra, DP-1 was the only variety where

yield for all four herbicide treatments were significantly lower than the non-treated.














CHAPTER 1
INTRODUCTION

In 2002, approximately 3.19 million hectares of peanut (Arachis hypogaea L.) were

harvested in the United States with an average yield of 2,870 kg/ha (United States

Department of Agriculture 2002). This was a 5% reduction from 2001 and a 4%

reduction from 2000. Growers in the Southwest (New Mexico, Oklahoma, and Texas)

planted 180,000 hectares of peanut in 2001, 16% less than 2000. Plantings in the

Virgina-North Carolina region totaled 67,000 hectares a 17% reduction from 2001.

These changes in peanut production were most likely the result of change in farm

subsidize programs that resulted in a less favorable pricing structure than was available

under previous legislation.

The Southeast (Alabama, Florida, Georgia, and South Carolina) is the largest

peanut production region in the United States with over 350,000 hectares planted in 2002,

an increase of 6% from 2001 (USDA 2002). Florida is ranked 5th nationally in peanut

production with Jackson County being the 3rd leading peanut producing county in the

United States. In 2002, Florida growers harvested 35,000 hectares with an average yield

of 2,600 kg/ha (Aerts and Nesheim 2000). States with the highest average yield in 2002

were Texas: 3,500 kg/ha, New Mexico: 3,400 kg/ha, Oklahoma: 3,100 kg/ha, Georgia:

2,900 kg/ha, and Florida: 2,600 kg/ha (USDA 2002).

Since 1990, the price per kilogram received for peanut has declined considerably

from $0.66/kg to the current price of less than $0.40/kg. The 2002 Farm Bill is an

important factor in determining profit potential of peanuts. Farmers were receiving









$0.67/kg quota price but that changed with the 2002 Farm Bill to $0.39/kg. According to

Dr. Nathan Smith from the University of Georgia, the variable cost for peanut production

will be lower for 2003 averaging $0.29/kg for non-irrigated and $0.33/kg for irrigated

compared to $0.42 for non-irrigated and $0.52 for irrigated in 2002. The factor having

the most significant impact on variable cost will be the price of seed and seed price has

declined as a result of the lower price paid for peanut (Smith 2003).

Current Management Strategies

Pest management accounts for a large portion of the variable production costs for

peanut. More than 36% of the total operating costs are invested in pesticides. In peanut,

there are over 43 weed species, 20 insect pests, 17 disease and 4 nematode pathogens that

are of economic importance in 9 peanut producing states. The worst weed pests, if left

uncontrolled, can reduce yield 30-80 percent in infested areas (Aerts and Nesheim 2000).

The most troublesome weeds in Florida peanut fields in 2001 were 1) Florida

beggarweed (Desmodium tortuosum L.) 2) sicklepod (Senna obtusifolia L.) and 3)

nutsedge spp. (Cyperus spp.) (Webster 2001). Peanut yields were reduced 15.8 to 30.2

kg/ha by Florida beggarweed and 6.1 to 22.3 kg/ha by sicklepod for each weed per 10 m2

(Hauser et al. 1982).

Peanut weed control is accomplished through cultural, mechanical, and chemical

methods. Crop rotation has many benefits and one of these is the better weed control that

can be a benefit to crop rotations most likely the benefit is to rotate herbicides.

Continuous use of a single mode-of-action herbicide can lead to development of

resistance where weed biotypes that were once controlled are no longer affected by that

herbicide.









Adoption of reduced tillage cropping practices that rely on in-crop selective

herbicides has lead to widespread change of rigid ryegrass (Lolium rigidum Gaud.) and

wild radish (Raphanus raphanistrum L.) populations in Western Australia with resistance

to acetolactate synthase (ALS)-inhibiting herbicides (Walsh et al. 2004). ALS herbicides

were introduced in 1982 and due to continuous use, resistance was first reported in 1987

(Walsh et al. 2001). By 1999, ALS-herbicide resistance had developed in 83 weed

species worldwide (Heap 2000). Mixing herbicides with different modes of action

reduces the probability of weed resistance and weed shifts. Cultivation may also be

utilized to slow the onset of weed resistance.

In peanut, the most effective weed control and highest yields have generally been

obtained using a herbicide program consisting of a preplant incorporated (PPI) or

preemergence (PRE) treatment followed by an at cracking (AC) stage treatment when the

plant is just emerging through the soil surface followed by a postemergence (POST)

application (Ducar et al. 2002). Traditional herbicide applications have included

pendimethalin or ethalfluralin PPI for control of annual grasses and small seeded

broadleaf weeds followed by a PRE application of diclosulam, flumioxazin, metolachlor,

or norflurazon for additional control of broadleaf weeds. At cracking and POST

herbicides most commonly used in Florida peanut production include paraquat for broad

spectrum early season weed control; bentazon for control of yellow nutsedge (Cyperus

esculentus L.) and various broadleaf weeds; 2,4-DB for control of morningglory spp.

(Ipomoea spp.) and sicklepod (Senna obtusifolia L.); chlorimuron or imazapic for late

season Florida beggarweed (Desmodium tortuosum sw. DC), nutsedge, and multiple

broadleaf weed species control (Ducar et al. 2002).









Traditional herbicide practices require that the herbicides previously mentioned be

applied at the full labeled rate. With the reduction of revenue due to the new Farm Bill,

farmers will need new tactics to reduce their production cost possibly by configuring

herbicide treatment combinations that will reduce the cost of weed management.

Diclosulam, Flumioxazin, and Imazapic

Over the past 6 years, three herbicides (diclosulam, flumioxazin, and imazapic)

have been introduced for broad-spectrum weed control in peanut production. Two of

these herbicides (diclosulam and imazapic) have a similar mode-of-action. Either of

these can be tank mixed with the third (flumioxazin) to get broad-spectrum weed control

while reducing the likelihood of developing weed resistance.

Diclosulam, [N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-

c]pyrimidine-2-sulfonamide], is a new triazolopyrimidine sulfonanilide herbicide from

Dow AgroSciences registered in peanut. It received Section 3 label in 2000 for use in

peanut as a soil applied herbicide for broadleaf weed control. Diclosulam can be applied

PPI, preplant surface, or PRE through true AC at the maximum rate of 27 g ai/ha.

Rotational restrictions for various crops do exist for this herbicide. There is a 10

month restriction for cotton and an 18 month restriction for corn, however, some research

indicates these restrictions may not be necessary. Cotton, corn and sorghum planted the

year following diclosulam applied at up to three times the labeled rate showed no

difference in fresh or dry weights of any crop (Gerngross and Senseman 2002).

Diclosulam is absorbed through the roots and shoots of germinating seedlings as

they grow and expand through the soil. Exposure to diclosulam prevents sensitive weed

seedlings from emerging, or if they do emerge they do not develop beyond the cotyledon

stage. Diclosulam inhibits the acetolactate synthase (ALS) enzyme that is involved in the









synthesis of branched chain amino acids isoleucinee, leucine, and valine) that are required

for plant growth (Vencill 2002).

Flumioxazin, (2-[7-fluoro-3,4-dihydro-3-oxo-4-(2-propynyl)-2H-1,4-benzoxazin-6-

yl]-4,5,6,7-tetrahydro- lH-isoindole-1,3 (2H)-dione), is a new herbicide developed by

Valent USA Corp. for broadleaf weed control in cotton (Gossypium spp.), peanut,

sugarcane (Saccharum officinarum L.), and soybean (Glycine max L.). Flumioxazin is a

N-phenylpthalimide derivative, which is new chemistry for peanut, cotton, and

sugarcane. The mode of action of this family is inhibition of the protoporphyrinogen

oxidase (PPO) causing peroxidation of membrane lipids, which leads to damage of

membrane functions.

Flumioxazin may be applied to peanut prior to planting as a preplant burndown or

PRE at 70 tol05g ai/ha depending on the weed species and/or the weed density (Cranmer

et al. 2000). Preemergence applications must be made within 2 days after planting.

Applications after peanut have begun to crack or emerge result in severe crop injury.

Rotational restrictions do exist for flumioxazin, however, the rotational interval is shorter

compared to other herbicides. Cotton, field corn, rice, sorghum, tobacco, wheat, and

sugarcane may be planted 30 days after application for the 70g ai/ha rate and 2 months

for the higher rate (Valor 2001).

Imazapic, [(+,-,)-2-[4,5-dihydro-4-methyl-4-(1 -methylethyl)-5-oxo- 1H-imidazol-2-

yl]-5-methyl-3-pyridinecarboxylic acid], is an imidazolinone herbicide produced by

BASF and was labeled for use in peanut in 1996. It is applied to approximately 75 % of

Florida's peanut hectarage at a rate of 70g ai/ha early POST. Imazapic controls various









broadleaf weeds, grasses, yellow and purple nutsedge and can be applied over the top of

peanut without causing crop damage.

Similar to diclosulam, imazapic inhibits acetolactate synthase (ALS), a key enzyme

in biosynthesis of the branch-chain amino acids (Vencill 2002). Compared to the

previously described herbicide, imazapic has very strict rotational restrictions. Nine

months must pass after imazapic application before planting field corn, soybean, tobacco,

snap, and southern pea. There is an 18 month interval between imazapic application and

planting of cotton, grain sorghum, sweet corn, and oats (Cadre 2001). Significant cotton

damage has been observed when it was planted the season following imazapic application

to peanut. In one study, cotton injury was greater than 50% 2 wk after planting (WAP)

when 9 to 36 g ai/ha was applied and greater than 60% injury at 6 WAP (Dotray et al.

2002).

Reduced Rate Herbicide Research

Peanut is a high management, high input crop with the cost of inputs steadily

increasing. Overall, yields have not increased for several years, even with new varieties

and technological advances. To remain competitive in a global market, farmers must find

ways to improve production efficiency or increase yields (Wright et al. 2001). Reducing

the amount of herbicides applied can help reduce the 36% of production cost due to

pesticide applications.

Research has been conducted using the full labeled rates of imazapic, diclosulam

and flumioxazin alone and in mixtures to examine weed control, peanut tolerance, and

yield. Weed control has been successful at these rates. Research has also been

conducted using these same three herbicides but at reduced rates in peanut in an attempt









to maintain weed control while reducing cost and to reduce the potential for imazapic

carryover.

Previous research indicates that imazapic, diclosulam, and flumioxazin can be

applied at reduced rates and still provide adequate weed control. Swann conducted a

study in 2000 that evaluated diclosulam applied PRE at 8.8 (.33X), 17.7 (.66X), and 26.5

(IX) g ai/ha to peanuts. Yellow nutsedge (Cyperus esculentus L.) control was greater

than 83% and control of common ragweed (Ambrosia artemisiifolia L.) was greater than

78%. When reduced rates of diclosulam were followed by imazapic applied early POST,

also at reduced rates, yellow nutsedge control increased to 88% and common ragweed

control increased to 99% (Swann 2000). Troxler et al. (2001) conducted a study with

diclosulam applied at 13g/ha (.5X) and flumioxazin applied at 52 g ai/ha (.5X). He

concluded that weed control was comparable to the IX rates for the two herbicides for all

weeds evaluated. When diclosulam and flumioxazin applied at .5X were followed by

imazapic applied at 35g/ha (.5X) it was concluded that these rates provided similar weed

control to the regional standard. In Northwest Texas at one location, yellow nutsedge

control was 85% or greater with imazapic applied at the 1/2X rate in combination

diclosulam at the 1/2X rate. At the second location, yellow nutsedge control was less

than 70%. In South Texas, imazapic applied alone at the 1/2X rate or used in

combination with diclosulam at 1/2X rate controlled Palmer amaranth (Amaranthus

palmeri S.), smellmellon (Cucumis melo L), and yellow nutsedge 80% or greater

(Baughman et al. 2003).

Row Spacing Research

Improving production efficiency and yield is essential for peanut producers to

remain competitive. Closer spacing of rows is one way to improve yield that has been









studied since the early 1900's but has not been adopted by farmers until recently. Parham

(1942) reported that Spanish peanut yields were higher in 46 cm rows than in 61, 76, 91,

and 107 cm rows. Due to cultivation requirements he suggested a spacing of 67 to 76 cm

as the most practical.

More recent studies indicate that planting peanut in a twin row spacing pattern

increases yields, decreases incidents of Tomato Spotted Wilt Virus (TSWV), and may

increase grade by 1 to 2% compared to traditional single row patterns. TSWV affects

peanut by decreasing yield and decreasing sound mature kernel percentage (TSMK)

(Baldwin et al. 1998). In a twin-row system, peanut row centers remain 91 centimeters

apart with the seeds planted in rows on each side of the 91 cm center with the twin rows

spaced 19 to 23 cm apart. The seeding rate per hectare is the same for twin-row spacing

with three seed per 30.5 cm for each row versus conventional row spacing with six seed

per 30.5 cm for one row.

Twin-row planting scheme results in quicker canopy coverage (as much as two

weeks earlier) which helps in weed control and higher grades due to a greater taproot

crop and less of a limb crop (Wright et al. 2001).

Wehtje et al. (1984) studied the effect of twin-row spacing on 'Florunner'

production and reduced herbicide applications. The results showed that yields improved

in twin rows only when weed competition was reduced to a minimum and that,

consequently, weed control inputs could not realistically be reduced. In 1985, Colvin et

al. studied the effects of row patterns and weed management systems on weed control,

peanut yield, and net return. Broadleaf fresh weights were significantly lower for the

dual pattern in 1981 and grass fresh weight significantly lower in 1983. Peanut yields









were higher for the dual pattern in 1981 and 1983 and equal to the standard in 1982. The

average net returns were higher for the dual pattern when compared to conventional.

In 1986, Cardina et al. studied weed control using reduced rates of standard

herbicides on 'Sunbelt runner' planted in twin-row patterns. A 30-60% reduction in

residual herbicide rates resulted in weed control and crop yield equivalent to the standard

treatment. He concluded that there was potential for reducing herbicide inputs in twin-

row peanut without sacrificing yield or quality (Cardina et al. 1986). Sicklepod density

in plots treated with dimethenamid-P alone was approximately 2/m2 in 2001 and 40/m2

in 2002. Sicklepod control was 9 and 11% higher in twin rows compared with single

rows when evaluated late in the growing season (Lanier et al. 2003). This data suggest

that seeding peanut in twin rows improve weed control when compared with seeding in

single rows.

A field study was conducted by in Texas evaluated the impact of reduced and full

rates of imazapic and diclosulam when applied to peanut in twin row and conventional

planting configurations. Averaged across all treatments yellow nutsedge control was

significantly better in the twin row spacing (87%) compared to conventional row spacing

(70%) (Besler et al. 2002).

Yield increases of 565 and 426 kg/ha were observed with 'Florunner' and 'Southern

Runner', respectively, when grown in twin rows compared to single rows in 1992

(Beasley et al. 1992). In twin rows, the 3 seeds per 30.5 centimeters of Georgia Green

cultivar resulted in significantly higher yields (4625 vs. 4301 kg/ha) and less TSWV

(12% vs. 18%) when compared to 2 seeds per 30.5 centimeters. Net returns for two,









three, or four seeds per 30.5 centimeters of row were $328, $437, and $264/ha

respectively (Baldwin et al. 2000).

When four different peanut cultivars ('Georgia Green', 'ViruGard', 'SunOleic 97R',

and 'Flavor Runner 458') were planted in twin rows versus single rows the results were

similar to previous research. When averaged across cultivars and locations, the twin row

pattern resulted in significantly higher yield and total sound mature kernel (TSMK) and

significantly reduced other kernel (OK) and TSWV incidence (Baldwin et al. 1998). The

response of another cultivar (VA 98R) to twin row planting versus single row planting

resulted in yield increases ranging from 264 to 703 kg/ha and were obtained in four on-

farm tests. The increase in value averaged $341/ha (Mozingo and Swann 2000).

In 2001, a new Tomato Spotted Wilt Virus resistant peanut cultivar was released,

tested in a twin row pattern, and compared to a single row pattern. The results indicated

less TSWV in the twin row pattern compared to the single row (19.8% versus 6.9%)

(Baldwin et al. 2001). Less TSWV is the main reason for renewed interest in twin rows

because TSWV incidence has been increasing in the southeast since 1986. Research

since that time has shown that in the presence of TSWV there is a positive effect on yield

when seeding rates are high enough to establish a final stand count of at least four plants

per foot of row. Increasing seedling count, while guaranteeing a uniform stand, also

increases production costs.

New Peanut Varieties

Differential response to herbicides is common in peanut (Jordan et al. 1998). 'Early

Bunch', a Virginia market type peanut, exhibited early-season injury from naptalam plus

dinoseb and paraquat applied early post emergence (Brecke 1989). Imazapic reduced

percentage of extra large and jumbo kernels in 'Florunner' and 'Sunrunner" cultivars.









Imazapic injury was also reported with 'Florunner', 'Georgia Runner', 'GK 7', 'NC 7', 'NC-

V11', 'Southern Runner', 'Sunrunner', and 'Agra Tech VC-1' cultivars (Richburg et al.

1995).

Research in Texas has shown diclosulam applied PRE at 18 and 27 g ai/ha injured

'Flavor Runner 458', 'Sunoleic 97R', 'TX 977006', and 'Georgia Hi O/L' varieties 10 to

40% 14 DAT but did not injure 'Tamrun 96'. Injury remained 20 to 25% 42 DAT for the

'Flavor Runner 458' and 'Sunoleic 97R' varieties and 35 to 45% for the 'Georgia Hi O/L'

from diclosulam applied PRE at 27 g ai/ha (Murphree et al. 2003). In 2000, diclosulam

applied PPI at 18, 27, or 54g ai/ha to three runner market-type peanut cultivars, 'Georgia

Green', 'C-99R', and 'MDR 98', in Florida, resulted in no peanut injury and canopy

diameter was unaffected at any rate (Main et al. 2002). In much of the Southwestern

production area during 2000, diclosulam caused stunting, stand loss, and chlorosis to the

peanut canopy when applied PPI and PRE. Therefore, a supplemental label was issued in

2001 for Texas, New Mexico, and Oklahoma changing PRE application timing to no less

than five days after planting through at-cracking at 26.8g ai/ha. In addition, Oklahoma

can apply diclosulam preemergence immediately after planting through at-cracking only

at 20. Ig ai/ha (Strongarm 2001).

Peanut injury from flumioxazin has been inconsistent. Early-season injury has

been a minor concern with flumioxazin. Less than 5% injury 14 DAT was observed on

all varieties from flumioxazin applied PRE at 105g ai/ha (Murphree et al. 2002). In

North Carolina, early season peanut injury at 3 WAP was minimal (3% or less) in 1996

on seven Virginia-type peanut cultivars (NC 7, NC 12C, NC 9, NC 10C, NC-V 11, VAC

92R, AT VC 1) when flumioxazin was applied at 71 g ai/ha PRE.









In 1997, all peanut cultivars treated with flumioxazin PRE were injured 15 to 28%

at 3 WAP (Wilcut et al. 2001). This may have been due to the cold wet conditions during

the 2 wk after PRE treatment. In 2002, Main et al. observed similar results with runner-

type varieties. Up to 25% injury was observed from flumioxazin at 14 and 28 DAT.

Flumioxazin was registered in 2001 and during its first year, injury was reported in

Oklahoma, Georgia, North Carolina, and West Texas (Murphree et al. 2003). These

results indicate the importance of evaluating cultivars for tolerance to current herbicide

application practices.

In 2003, seven new peanut cultivars developed by Dr. D. W. Gorbet at the

University of Florida were released. These varieties have not been tested for their

tolerance to commonly used herbicides in peanut production ('Carver', 'ANorden', 'GP-1',

'DP-1', 'Hull', 'AP-3', and 'UF00324').

'ANorden' is a medium maturity (135-140 days) variety, with runner growth habit

(prominent center stem), runner size pods and seeds, very good TSWV resistance, and

with high oleic oil chemistry. It is a replacement for 'SunOleic 97R' in the Florida

Foundation Seed Producers program. 'ANorden' has shown pod yields equal to or better

than 'Georgia Green' in Florida tests and likewise for TSWV resistance, with somewhat

larger seed size. 'ANorden' has been equal to 'Georgia Green' in resistance to white mold,

leaf spot, and rhizoctonia disease.

'DP-1' is a late maturity (150+ days) cultivar with excellent disease resistance. It

has the highest level of resistance to late leaf spot, TSWV, and white mold currently

available in a US peanut cultivar. Yield in excess of 5000 kg/ha has been recorded in









Florida tests without fungicide applied for leaf spot control. 'DP-1' has "normal" oil

chemistry and seed size similar to 'GK 7'. It has somewhat less vine growth than 'C-99R'.

'Carver' is a medium maturity (135-140 days), runner growth habit, runner pod, and

seed size. It has TSWV and white mold resistance that is somewhat better than 'Georgia

Green' with some resistance to CBR, Rhizoctonia limb rot and late leaf spot. 'Carver' has

excellent yield potential with somewhat larger and elongated seeds that have "normal" oil

chemistry.

'Hull' is a late maturity (150+ days) jumbo runner seed size, high oleic cultivar with

excellent pod yields and multiple disease resistance in Florida studies. 'Hull' has

resistance to TSWV and late leaf spot similar to 'C-99R' but better than 'Georgia Green'.

It has white mold resistance equal to or better than C-99R and better than 'Georgia

Green'. 'Hull' also has some good resistance to CBR and some root knot nematode

resistance. Its seed size is similar to 'C-99R', with somewhat less vine growth. The

major advantage of this new peanut is its greatly improved oil chemistry compared to all

normal chemistry varieties. High oleic varieties have about 80% oleic and only 2-3%

linoleic fatty acid based on total fat content, which greatly improves shelf life of products

made from seed of this variety.

'GP-1' has early maturity (125-130 days) in Florida test with high oleic oil

chemistry, runner seed size, and intermediate runner growth habit. 'GP-1' has some

TSWV resistance but less than 'Georgia Green'. Pod yields have been equal to 'GA

Green' only in low TSWV pressure situations however seed size is somewhat larger

(Gorbet et al. 2002).









'AP-3' is a new variety of peanut that was released in 2003 by Dr. D. W. Gorbet and

will only be marketed by Anderson's Peanut Co. This variety is a medium maturity (135-

140 days) with runner growth habits. It is a sister line of 'Carver' and 'NC 3033' variety

developed by North Carolina with good yield. It has excellent TSWV resistance, good

white mold and CBR resistance better than that of 'Carver' variety. 'AP-3' is not a high

oleic variety. The grading of this variety is slightly lower than that of 'Carver' mainly due

to the thicker hull of'AP-3'.

'UF00324' is a new variety not yet approved for release and is still under

evaluation. It's a medium maturity (135-140 days) variety with runner growth habits,

good yield and grades similar to 'Carver' with larger seed size. 'UF00324' has good

TSWV resistance similar to 'Carver'. This variety is not high oleic and it's not yet known

if there is resistance to white mold or CBR.

Summary

Because of previous research results and the high value of peanut, growers have

been reluctant to implement reduce rate herbicide application. However, with the recent

introduction of new herbicides and change in government program that lowered the value

of peanut, growers are now interested in reducing input costs, especially cost of weed

management.

With the benefits of twin-row planting including more rapid canopy closure, reduce

TSWV, higher yields, and increase grade leading to increased revenue, research to

determine effectiveness of reduced herbicide rates in a twin row system appears justified.

Since twin row pattern achieves canopy cover at least two weeks earlier than

conventional row spacing, weed suppression is possible and may require less herbicide

inputs.









Minimal research has been conducted in the area of reduced herbicide rates in both

conventional and twin-row spacing regimes. The goal of this research was to evaluate

diclosulam, flumioxazin, and imazapic for weed management and peanut yield applied at

reduced rates to both twin and single row spacing production systems. Economic

analysis was also conducted for these two situations. In addition, a study was conducted

with commonly used herbicides used in reduced cost combinations for peanut weed

management. An additional test evaluated seven new peanut cultivars for response to

various commonly used herbicides.














CHAPTER 2
EFFECTS OF REDUCED APPLICATIONS OF DICLOSULAM, FLUMIOXAZIN,
AND IMAZAPIC ON WEED MANAGEMENT IN PEANUT (ARACHIS
HYPOGAEA L.) PRODUCTION

Introduction

Peanut is a high management, high input crop with the input costs steadily

increasing. Overall, yields have not increased for several years, even with new varieties

and technological advances. To remain competitive in a global market, farmers must find

ways to improve production efficiency or increase yields (Wright et.al 2002). Reducing

the amount of herbicides applied can help reduce the 36% of production cost due to

pesticide applications (Aerts 2000).

Imazapic, diclosulam and flumioxazin alone and in mixtures provided control of

many broadleaf weeds in peanut when applied at the full label rates (Troxler et al.2001).

Weed control has been successful at these rates. Research has also been conducted using

these same three herbicides but at reduced rates in peanut in an attempt to maintain weed

control while reducing cost and to reduce the potential for imazapic carryover

(Baughman et al.2003; Swann et al. 2000). Swann (2000) reported that diclosulam

applied at 8.8 (.33X) (0.33 of the labeled rate), 17.7 (.66X), and 26.5 (1X)g ai/ha to

peanut controlled yellow nutsedge (Cyperus esculentus L.) >83% and control of common

ragweed (Ambrosia artemisiifolia L.) was >78%. When reduced rates of diclosulam were

followed by imazapic applied early postemergence, also at reduced rates, yellow

nutsedge control increased to 88% and common ragweed control increased to 99%

(Swann 2000).









Troxler et al. (2001) conducted a study using diclosulam applied at 13 g/ha (1/2x)

and flumioxazin applied at 52 g ai/ha (1/2x). He concluded that weed control was

comparable to the IX rates for the two herbicides for all weeds evaluated. When

diclosulam and flumioxazin applied at 1/2x were followed by imazapic applied at 35 g/ha

(1/2x) weed control was similar to that observed with the regional standard. In

Northwest Texas at one location, yellow nutsedge control was at least 85% with imazapic

applied at the 1/2X rate in combination with diclosulam at the 1/2X rate at one location

while at a second location control of yellow nutsedge was less than 70%. In South Texas,

imazapic applied alone at the 1/2X rate or in combination with diclosulam at 1/2X rate

controlled Palmer amaranth (Amaranthus palmeri S.), smellmellon (Cucumis melo L),

and yellow nutsedge at least 80% (Baughman et al. 2003).

Improving production efficiency and yield is essential for peanut producers to

remain competitive. Closer spacing of rows, one way to improve yield, has been studied

since the early 1900's but was not adopted by farmers until recently. More recent studies

indicate that planting peanut in a twin-row spacing pattern increase yields, decrease

incidents of Tomato Spotted Wilt Virus (TSWV), and may increase grade by 1 to 2%.

This planting scheme results in quicker canopy coverage (as much as 2 wk earlier) which

aids in weed control and results in higher grade since peanut tends to put on more of a

taproot crop and less of a limb crop (Wright et al. 2001). In 1986, Cardina et al. studied

weed control using reduced rates of standard herbicides on 'Sunbelt runner' planted in

twin-row patterns. A 30-60% reduction in residual herbicide rates resulted in weed

control and crop yield equivalent to the standard treatment. He concluded that there was









potential for reducing herbicide inputs in twin-row peanut without sacrificing yield or

quality (Cardina et al.1986).

Because previous research indicated sometimes negative results and the high value

of peanut, growers were reluctant to implement reduced rate herbicide application.

However, with the recent introduction of new herbicides and change in government

program that lowered the value of peanut, growers are now interested in reducing input

costs, especially cost of weed management.

In a more recent study, sicklepod (Senna obtusifolius L.) density in plots treated

with dimethenamid-P alone was approximately 2/m2 in 2001 and 40/m2 in 2002.

Sicklepod control was 10% higher in twin rows compared with single rows when

evaluated late in the growing season (Lanier et al. 2003).

With the benefits of twin-row planting including more rapid canopy closure,

reduced TSWV, higher yields, and increased grade leading to increased revenue, research

to determine effectiveness of reduced herbicide rates in twin rows appears justified.

Studies conducted thus far have focused on comparing one-half with full rate application

combinations of herbicides. With new interest in reducing input cost, the objective of

this study was to determine if adequate weed management could be achieved in peanut at

rates lower than 1/2x combinations of diclosulam, flumioxazin, and imazapic in both

single and twin-row spacing.

Materials and Methods

Field studies were conducted in 2002 and 2003 at the West Florida Research and

Education Center near Jay, FL, the North Florida Research and Education Center near

Marianna, FL, and at the Plant Science Research and Education Center near Citra, FL.

Jay is located in the far West panhandle of Florida with soil type of Red Bay Sand Loam









(fine-loamy, siliceous, thermic, Rhodic paleudults) at pH 5.8 and organic matter of 2.1%.

Marianna is located in the central panhandle with Chipola loamy sand (loamy, siliceous,

thermic, Arenic hapudult) soil type containing 1.0% organic matter and pH of 6.2. Citra

is located in North Central Florida with soil type Sparr sand (loamy, siliceous,

hyperthermic, Grossa-renic paleudult) with organic matter 1% and pH of 6.4.

Conventional tillage system consisting of deep moldboard plowing, leveling disking and

one field cultivation prior to planting was used to prepare the field for peanut planting.

Pendimethalin was applied at 1.12 kg ai/ha pre plant incorporated (PPI) to the entire test

at all locations for control of small-seeded broadleaf and annual grasses.

The peanut variety C-99R was planted on May 6, 8, and 9, 2002 at Marianna, Citra,

and Jay, FL, respectively and on April 30 and May 5, 2003 at Citra and Jay FL

respectively. Peanut was planted at a depth of 6 cm with a seeding rate of 122 kg/ha.

Row spacing was 91cm single rows in 2002 at Jay, Citra and Marianna and in 2003 at Jay

and Citra. In 2003, peanut were also planted in twin rows 20 cm apart on 91 cm spacing

in addition to the single row test at Jay and Citra. Plots at Citra were four rows, 3 m wide

and 6.1 m long. Plots at Jay and Marianna were four rows, 3 m wide and 7 m long.

Treatments were arranged in a randomized complete block design with 4 replications.

Soil fertilization and liming practices were in accordance with test

recommendations by the University of Florida Soil Testing Laboratory. Florida

Cooperative Extension Service recommendations were followed for management of

fungicide, insecticide, and irrigation.

Herbicide treatments and application rates are listed in tables 2.1 and 2.2 include

diclosulam and flumioxazin applied preemergence (PRE) alone and as tank mixtures at









1/4, 1/2, and full labeled rates. Imazapic at 1/4, 1/2, 2/3, and full labeled rates early

postemergence (EPOST) following PRE diclosulam and/or flumioxazin treatments. All

EPOST applications of imazapic included a non-ionic surfactant (Induce) of 0.25 % V/V.

Herbicides were applied with a C02 pressurized backpack sprayer calibrated to deliver

187 L/ha.

Weed control was visually evaluated using a scale of 0 (no control) to 100

(complete control) early season -35 days after planting (DAP), and late season, -120

DAP, during the growing season. The center two rows from each plot were harvested

with conventional equipment approximately 140-148 DAP at physiological maturity as

determined by the hull scrape method (Johnson 1987). Plot yields were converted to

yield per hectare at 8% moisture.

Economic returns were determined for each treatment based on yield per hectare

utilizing the following formula:

Yield/hectare @ $0.50 per kg $1358/ha (total production cost) herbicide cost/ha

The price per ton and total production cost was based on the average Florida peanut

grower values as determined through conversation with University of Florida's Extension

Agricultural Economist. Herbicide prices used in the analysis were obtained from several

farm supply stores throughout Florida's peanut production region.

SAS (1996) Proc GLM software was used to analyze the data. Data were subjected

to analysis of variance to test treatment effects and interactions. Means were separated

using Fisher's Protected LSD Test at the p<0.1 level.









Results and Discussion

Treatments in 2002 were different from 2003 and location interactions for all

parameters measured prevented pooling of data. Therefore, data is presented by location

and year.

Weed Control-2002

Predominant weeds at Jay were common cocklebur (Xanthium strumarium L),

sicklepod (Senna obtusifolia L.), and yellow nutsedge (Cyperus esculentus L.).

Diclosulam and flumioxazin at all rates applied alone did not adequately control the weed

species present (Table 2.4). Diclosulam at 1/4x and Ix PRE controlled yellow nutsedge

48 and 63% and sicklepod 9 and 25% greater than 1/4 and Ix rates of flumioxazin.

Diclosulam mixed with flumioxazin both at 1/4x increased sicklepod control over

diclosulam alone at 1/4x or flumioxazin alone at 1/4x and Ix rate. Preemergence

treatments followed by imazapic EPOST provided better control (85%) than PRE alone

for sicklepod and yellow nutsedge. Diclosulam mixed with flumioxazin at 1/4x PRE

followed by imazapic at Ix EPOST provided weed control equal to the Ix rates of PRE

and EPOST herbicides. Diclosulam plus flumioxazin applied PRE at 1/4x followed by

imazapic at 1/2x was the lowest level of herbicide input that provided greater than 85%

control of all weeds evaluated late season. Results with this treatment were comparable

to that observed with the regional standard.

Predominant weeds at Citra were pigweed (Amaranthus spp.), hairy indigo

(Indigofera hirsuta L.), and Florida beggarweed (Desmodium tortuosum (Sw) DC.).

Flumioxazin at the full rate alone PRE provided 95% control over all weeds evaluated

(Table 2.5). Other PRE treatments alone did not provide weed control >72% for hairy









indigo and Florida beggarweed; however, control was -20% greater with flumioxazin

than with diclosulam.

Diclosulam plus flumioxazin applied PRE both at 1/4x followed by imazapic at

2/3x was the lowest level of herbicide input that provided greater than 90% late season

control of all weeds evaluated and greater than Ix treatments.

Smallflower morningglory (Jaquemontia tamnifolia (L.) Greseb), and tropic croton

(Croton glandulosus L.) control at Marianna was greater than 85% for all treatments

except flumioxazin at 1/4x PRE fb imazapic at 1/4x EPOST (Table 2.6). However, none

of the treatments provided >60% control of yellow nutsedge and only Diclosulam at Ix

plus flumioxazin at Ix PRE fb imazapic at Ix provided >70% sicklepod control. Lack of

control was due to rain soon after the EPOST application of imazapic which requires at

least a 3 hour rain free period (Cadre 2001).

Weed Control-2003

Citra represented an area of relatively low weed pressure at approximately 1-3

weeds per m2 in the untreated checks for all but one species. The one species present at a

higher population (2 to 10 weeds per m2) is a new troublesome weed to Florida and parts

of Georgia in both cotton and peanut; tropical spiderwort (Commelina benghalensis L.).

This weed establishes quickly, and has prostrate growth therefore providing quick ground

cover, and is difficult to control. Quick growth and establishment of this weed may have

reduced the populations of the other weeds.

All treatments in both twin-and single-row studies provided 77% or greater control

of sicklepod, purple nutsedge (Cyperus rotundus L.), hairy indigo, and cutleaf

groundcherry (Physalis angulata L.) (Tables 2.7 and 2.8). Florida beggarweed control

was greater than 80% for all treatments except for diclosulam PRE treatments applied









alone at all rates in both the twin-and single-row studies and treatments with diclosulam

PRE at 1/4 and 1/2x followed by imazapic at 1/4x, flumioxazin at 1/2x followed by

imazapic at Ix, and imazapic alone EPOST at 1/4x in the single-row study.

Tropical spiderwort was the predominant weed at Citra. Tropical spiderwort was

controlled >80% in more treatments in the twin-row study than in the single-row study.

Diclosulam 1/4x applied with flumioxazin at 1/4x PRE followed by imazapic EPOST at

1/4x was the least herbicide input that provided greater than 80% tropical spiderwort

control in twin rows. In single rows diclosulam combined with flumioxazin PRE

followed by imazapic EPOST all at 1/2x was the herbicide combination that provided

86% control.

Jay was an area of relatively high weed pressure. Predominate weeds at this

location were sicklepod, purple nutsedge, Florida beggarweed, smallflower

morningglory, and wild poinsettia (Euphorbia heterophylla L.). All treatments in both

twin-and single-row studies provided greater than 87% control for smallflower

morningglory and wild poinsettia (Table 2.9 and 2.10). Full rate treatments and the

regional standard were required to control sicklepod greater than 85% in both row

spacing studies as was expected from previous experience with these three herbicides

(Prostko and Gray 2003 & 2004). Florida beggarweed control late-season was greater

than 85% in the single-row study except for diclosulam PRE alone at all rates, diclosulam

followed by imazapic at 1/4x, and when imazapic was applied alone EPOST at 1/4 and

1/2x. Flumioxazin at all rates alone or when followed by imazapic provided greater than

89% control late-season. Twin-row culture provided increased control (greater than

85%) of Florida beggarweed as opposed to the single-row system. Treatments with









diclosulam 1/4x PRE or imazapic 1/4x EPOST provided 77 and 80% control

respectively. Diclosulam at 1/4x applied with flumioxazin at 1/4x PRE was the only

treatment in the twin-row culture that provided less than 84% control of purple nutsedge.

Control of purple nutsedge was greater with diclosulam than with flumioxazin applied

alone for all rates in the single-row system.

Peanut Yield

There was no significant difference among treatments at Jay, Marianna, or Citra in

2002. Yield was much lower at Jay in 2002. This was due to a late-season infestation of

Cylindrocladium black rot (Cylindrocladium parasiticum) and the heavy rains from a

tropical storm that delayed drying and harvesting after digging and inverting was

complete. Flumioxazin at Ix yielded 1582 kg/ha more than flumioxazin at 1/4x (Table

2.11). Yield at Citra ranged from 2571 to 4459 kg/ha (non-treated and diclosulam with

flumioxazin at 1/4x, respectively) (Table 2.11). Flumioxazin applied at 1/4x PRE yielded

1253 kg/ha less than the highest yielding treatment, yielding only higher than the non-

treated control. Other treatments were not significantly different. Yield at Marianna was

the highest for treatments with flumioxazin at 1/4x PRE followed by imazapic at 1/2x and

flumioxazin plus diclosulam at 1/4x PRE followed by imazapic at 1/4x EPOST (4902 and

4953 kg/ha, respectively) (Table 2.12). The non-treated control yielded lowest at

3885kg/ha.

In 2003, there again was no significant difference among treatments (Table 2.14).

Diclosulam mixed with flumioxazin at 1/2x followed by imazapic at 1/2x treatment was

the highest yielding in the single row study at both locations (681 land 4824 kg/ha). This

treatment was also among the higher yielding (3rd and 4th) treatments in the twin row

study. The highest yielding treatments in both twin row studies were observed with









imazapic at 1/4x alone EPOST, flumioxazin at 1/4x alone PRE, and diclosulam at 1/4x

PRE followed by imazapic at 1/2x EPOST. Applications of imazapic EPOST following a

PRE application consistently resulted in increased yield (-300 kg/ha) at both locations

and in both row patterns except at Citra for flumioxazin applied PRE where the weed

pressure was low.

Economic Analysis

Total revenue at Citra and Jay in the single row study was highest with diclosulam

plus flumioxazin both at 1/2x followed by imazapic at 1/2x ($1981.68 and $986.00/ha,

respectively) (Table 2.14). The next highest return was with the combination of

diclosulam plus flumioxazin 1/4x followed by imazapic at Ix at Citra and flumioxazin

applied at 1/4x followed by imazapic at 1/2x at Jay ($1929.02 and $968.71/ha,

respectively). The highest total revenue in the Citra twin-row study was with imazapic

applied at 1/4x EPOST and next highest was with flumioxazin at 1/4x ($1770.30 and

$1701.43/ha, respectively). The lowest total revenue was observed with flumioxazin

followed by imazapic at Ix in the twin row study and diclosulam applied with

flumioxazin at 1/4x followed by imazapic at 2/3x in the single-row study ($656.49 and

$961.21/ha, respectively). Total revenue at Jay was highest with diclosulam mixed with

flumioxazin at 1/4x followed by imazapic at Ix ($864.68/ha).

Results from these studies indicate reduced rates of diclosulam and flumioxazin

followed by imazapic can be used in Florida peanut production, provide adequate weed

control without compromising yield and provide total revenue equal to or higher than the

regional standard. Diclosulam applied with flumioxazin PRE followed by imazapic

EPOST at 1/2x consistently (both years in twin-and single-row systems) produced total









revenue higher than the regional standard of paraquat plus bentazone AC fb imazapic

EPOST with treatment cost $3 less per hectare.

Since the passing of the 2002 Farm Bill, growers will have to compete in a global

market receiving the world price for their peanut which is significantly lower than the

previous government supported price. Peanut are a high management, high input crop

with the cost of inputs steadily increasing. To remain competitive, growers must find

ways in which to improve production efficiency. Reducing the amount of herbicides

applied is one way to reduce the 40% of total production cost that results from pesticides

(Aerts an Nesheim 2000).

Further research is needed to determine whether using reduced rates of imazapic

may decrease the potential for carryover to the next growing season so that rotational

restriction on cotton for the following year might be relaxed. Environmental effects such

as leaching of chemicals and ground water quality may also be reduced due to the lower

herbicide rates. With all the benefits of increased yield, increased grade, decreased

TSWV, and decreased weed populations proven in previous studies with twin-row

planting regimes, the additional benefit of effectively using reduced rates of herbicides

can only result in an increase in total revenue. They benefit the grower, consumer, and

the U.S. economy since peanut contributes over $4 billion to the economy each year

(USDA 2002).










Table 2.1-2002 Reduced rate treatments-Jav and Citra, FL.


Abbreviation


Treatment a'b


Rate


Portion of
labeled rate


g ai/ha


Check


NONTREATED

Diclosulam

Diclosulam

Flumioxazin

Flumioxazin

Flumioxazin +
Diclosulam

Flumioxazin +
Diclosulam fb
Imazapic

Flumioxazin +
Diclosulam fb
Imazapic

Diclosulam fb
Imazapic

Flumioxazin fb
Imazapic

Flumioxazin +
Diclosulam fb
Imazapic

Paraquat +
Bentazon fb
Imazapic


a All treatments including the check received pendimethalin PPI
b EPOST applications received surfactant at 0.25% V/V.
c "+" = tank mix, "fb" = followed by in a sequential treatment


1/4x


1/4x


6.72

26.8

26.3

105.3

26.3
6.72

26.3
6.72
35.3

26.3
6.72
47.1

26.8
70.6

105.3
70.6

26.3
6.72
70.6

140
280
70.6


1/4x
1/4x
Ix


) 1120 g ai/ha


Timing'


PRE

PRE

PRE

PRE


1/4x
1/4x

1/4x
1/4x
1/2x

1/4x
1/4x
2/3x


FL +
DS

FL +
DS fb
IM

FL+
DS fb
IM

DS fb
IM

FL fb
IM

FL+
DS fb
IM


PRE +
PRE


PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST


PAR+
BEN fb
IM









Table 2.2-2002 Reduced rate treatments-


Abbreviation


Check

DS fb
IM

DS fb
IM

DS fb
IM

DS fb
IM

FL fb
IM

FL fb
IM

FL fb
IM

FL fb
IM

DS+
FL fb
IM
DS+
FL fb
IM
DS+
FL fb
IM


Treatment a'b


Non-treated

diclosulam fb
imazapic

diclosulam fb
imazapic

diclosulam fb
imazapic

diclosulam fb
imazapic

flumioxazin fb
imazapic

flumioxazin fb
imazapic

flumioxazin fb
imazapic

flumioxazin fb
imazapic

diclosulam +
flumioxazin fb
Imazapic
diclosulam +
flumioxazin fb
imazapic
diclosualm +
flumioxazin fb
imazapic


-Marianna, FL
Rate Portion of
labeled rate
g ai/ha


6.72
17.6

6.72
35.3

13.4
17.6

13.4
35.3

26.3
17.6

26.3
35.3

52.6
17.6

52.6
35.3

6.72
26.3
17.6
13.4
52.6
35.3
26.8
105.3
70.6


1/4x
1/4x

1/4x
1/2x

1/2x
1/4x

1/2x
1/2x

1/4x
1/4x

1/4x
1/2x

1/2x
1/4x

1/2x
1/2x

1/4x
1/4x
1/4x
1/2x
1/2x
1/2x
Ix
Ix
Ix


a All treatments including the check received pendimethalin PPI
b EPOST applications received surfactant at 0.25% V/V.
c "+" = tank mix, "fb" = followed by in a sequential treatment


@ 1120 g ai/ha


Timing'


PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE fb
EPOST

PRE +
PRE fb
EPOST
PRE +
PRE fb
EPOST
PRE +
PRE fb
EPOST









Table 2.3-2003 Reduced rate treatments-Jay and Citra, FL.
Abbreviation Treatment"ab Rate Portion of Timing'
labeled rate
g ai/ha
Check Non-treated
DS diclosulam 6.72 1/4x PRE

DS diclosulam 13.4 1/2x PRE

DS diclosulam 26.8 Ix PRE

DS fb diclosulam fb 6.72 1/4x PRE fb
IM imazapic 17.6 1/4x EPOST

DS fb diclosulam fb 6.72 1/4x PRE fb
IM imazapic 35.3 1/2x EPOST

DS fb diclosulam fb 13.4 1/2x PRE fb
IM imazapic 17.6 1/4x EPOST

DS fb diclosulam fb 13.4 1/2x PRE
IM imazapic 35.3 1/2x EPOST

DS fb diclosulam fb 13.4 1/2x PRE fb
IM imazapic 70.6 Ix EPOST

DS fb diclosulam fb 26.8 Ix PRE fb
IM imazapic 70.6 Ix EPOST

FL flumioxazin 26.3 1/4x PRE

FL flumioxazin 52.6 1/2x PRE

FL flumioxazin 105.3 Ix PRE

FL fb flumioxazin fb 26.3 1/4x PRE fb
IM imazapic 17.6 1/4x EPOST

FL fb flumioxazin fb 26.3 1/4x PRE fb
IM imazapic 35.3 1/2x EPOST

FL fb flumioxazin fb 52.6 1/2x PRE fb
IM imazapic 17.6 1/4x EPOST

FL fb flumioxazin fb 52.6 1/2x PRE fb
IM imazapic 35.3 1/2x EPOST









Table 2.3 Continued
Abbreviation Treatment ab


FL fb
IM

FL fb
IM

FL fb
DS

FL+
DS fb
IM

FL+
DS fb
IM

FL+
DS fb
IM

FL+
DS fb
IM

FL+
DS fb
IM

FL +
DS fb
IM
IM
IM
Para +
Ben fb
IM


Rate Portion of
labeled rate
g ai/ha
52.6 1/2x
70.6 Ix

105.3 Ix
70.6 Ix


flumioxazin fb
imazapic

flumioxazin fb
imazapic

flumioxazin +
diclosulam

flumioxazin +
diclosulam fb
imazapic

flumioxazin +
diclosulam fb
imazapic

flumioxazin +
diclosulam fb
imazapic

flumioxazin +
diclosulam fb
imazapic

flumioxazin +
diclosulam fb
imazapic

flumioxazin +
diclosulam fb
imazapic
imazapic
imazapic
paraquat +
bentazon fb
imazapic


1/4x
1/4x

1/4x
1/4x
1/4x

1/4x
1/4x
1/2x

1/4x
1/4x
2/3x

1/4x
1/4x
Ix

1/2x
1/2x
1/2x

Ix
Ix
Ix
1/4x
1/2x


26.3
6.72

26.3
6.72
17.6

26.3
6.72
35.3

26.3
6.72
47.1

26.3
6.72
70.6

52.6
13.4
35.3

105.3
26.8
70.6
17.6
35.3
140
280
70.6


Timing'


PRE fb
EPOST

PRE fb
EPOST

PRE +
PRE

PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST

PRE +
PRE fb
EPOST
EPOST
EPOST
AC +
AC fb
EPOST


" All treatments including the check received pendimethalin PPI C 1120 g ai/ha
b EPOST applications received surfactant at 0.25% V/V.
c "+" = tank mix, "fb" = followed by in a sequential treatment










Table 2.4-Weed control as affected by reduced rate herbicide treatments in 2002 at Jay,
FL
Late Season"
TRTb,c,d XANST CASOB CYPES
----------------------% Control---------------------------------
Check 0 0 0
DS 1/4x 86 45 76
DS Ix 97 72 93
FL 1/4x 65 36 28
FL Ix 75 47 30
DS +FL1/4x 88 70 75
DS + FL 1/4x fb 97 85 95
IM 1/2x

DS + FL 1/4x fb 95 86 97
IM 2/3x

DS + IM Ix 97 95 100
FL + IM Ix 97 95 100
DS + FL 1/2fb 98 92 100
IM 1/2x

Par + Ben lx fb 87 97 100
IM Ix
LSDe 18.2 18.5 20
a XANST -Xanthuim strumarium CASOB Senna obtusifolia CYPES Cyperus esculentus
b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
' All treatments including the check received pendimethalin PPI @( 1120 g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.










Table 2.5-Weed control as affected by reduced rate herbicide treatments in 2002 at Citra,
FL
Late Season a
TRT b,c,d AMASP INDHI DEDTO
-----------------o Control----------------------------
Check 0 0 0
DS 1/4x 92 52 52
DS Ix 93 67 67
FL 1/4x 41 72 72
FL Ix 95 95 95
DS +FL1/4x 92 78 78
DS + FL 1/4x fb 93 71 71
IM 1/2x

DS + FL 1/4x fb 93 93 93
IM 2/3x

DS + IM Ix 92 70 70
FL + IM Ix 91 86 86
DS + FL /2 fb 40 83 83
IM 1/2x
LSD e 6.2 24.2 24.2
A i. 1 '-Amaranthus spp INDHI Indigofera hirsute DEDTO Desmodium tortuosum
b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
' All treatments including the check received pendimethalin PPI @ 1120g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.










Table 2.6-Weed control as affected by reduced rate herbicide treatments in 2002 at
Marianna, FL
Late Seasona
TRT b,c,d CYPES IAQTA CASOB CVNGL
------------------------- Control------------------------------
DS 1/4x fb IM 1/4x 32 99 26 89
DS 1/4x fb IM 1/2x 32 99 35 99
DS 1/2x fb IM 1/4x 21 99 35 99
DS 1/2x fb IM 1/2x 35 99 40 99
FL 1/4x fb IM 1/4x 12 73 12 99
FL 1/4x fb IM 1/2x 27 89 40 86
FL 1/2x fb IM 1/4x 35 95 30 99
FL 1/2x fb IM 1/2x 30 96 18 99
DS 1/4x + FL 1/4x fb 27 99 37 99
IM 1/4x
DS 1/2x + FL 1/2x fb 57 99 55 99
IM 1/2x
DS lx+FL lxfb 55 99 72 99
IM Ix
Check 0 0 0 0
[Efe 204 9 2 2 7 109
a IAQTA Jaquemontia tamnifolia CVNGL Croton glandulosus CASOB Senna obtusifolia
CYPES Cyperus esculentus
b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
' All treatments including the check received pendimethalin PPI @( 1120g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.









Table 2.7-Weed control as affected by reduced rate herbicide treatments in 2003 at Citra,
FL in single row study
Late Season"
TRTb,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBA
----------------------------0% Control-----------------------------


DS 1/4x
DS 1/2x
DS Ix
DS1/4x fblIM 1/4x
DS 1/4x fb IM 1/2x
DS 1/2x fb IM 1/4x
DS 1/2x fb IM 1/2x
DS 1/2x fb IM Ix
DS Ix fb IM Ix
Check
FL 1/4x
FL 1/2x
FL Ix
FL 1/4x fb IM 1/4x
FL 1/4x fb IM 1/2x
FL 1/2x fb IM 1/4x
FL 1/2x fb IM 1/2x
FL 1/2x fb IM Ix
FL Ix fb IM Ix
DS 1/4x + FL 1/4x
DS 1/4x + FL 1/4x fb
IM 1/4x
DS 1/4x + FL 1/4x fb
IM 1/2x
DS 1/4x + Fl 1/4x fb
IM 2/3x
DS 1/4x + FL 1/4x fb
IM Ix
DS 1/2x + FL 1/2x fb
IM 1/2x
DS lx+FL Ixfb
IM Ix
IM 1/4x
IM 1/2x


99 99

99 99

99 96

99 96

99 93


97 99


96 99










Table 2.7 Continued
Late Season"
TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBA
----------------------------0% Control-----------------------------
Par Ix + Ben Ix fb
IM Ix 99 99 91 97 99 75
Check 0 0 0 0 0 0
LSDe 12.8 11 22.7 6.4 2.5 19.2

a CASOB Senna obtusifolia CYPRO Cyperus rotundus INDHI Indigofera hirsute DEDTO -
Desmodium tortuosum PHYAN Physalis angulata COMBA Commelina banghalensis
bDS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
c All treatments including the check received pendimethalin PPI @ 1120g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.









Table 2.8-Weed control as affected by reduced rate herbicide treatments in 2003 at Citra,
FL in twin row study
Late Season"
TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBAT
-----------------------------% Control------------------------------


DS 1/4x
DS 1/2x
DS Ix
DS1/4x fblIM 1/4x
DS 1/4x fb IM 1/2x
DS 1/2x fb IM 1/4x
DS 1/2x fb IM 1/2x
DS 1/2x fb IM Ix
DS Ix fb IM Ix
Check
FL 1/4x
FL 1/2x
FL Ix
FL 1/4x fb IM 1/4x
FL 1/4x fb IM 1/2x
FL 1/2x fb IM 1/4x
FL 1/2x fb IM 1/2x
FL 1/2x fb IM Ix
FL Ix fb IM Ix
DS 1/4x + FL 1/4x
DS 1/4x + FL 1/4x fb
IM 1/4x
DS 1/4x + FL 1/4x fb
IM 1/2x
DS 1/4x + Fl 1/4x fb
IM 2/3x
DS 1/4x + FL 1/4x fb
IM Ix
DS 1/2x + FL 1/2x fb
IM 1/2x
DS lx+FL Ixfb
IM Ix
IM 1/4x
IM 1/2x


96 94

99 94

92 94

99 87

99 94


97 99

97 99

96 99










Table 2.8 Continued
Late Season"
TRT b,c,d CASOB CYPRO DEDTO INDHI PHYAN COMBAT
----------------------------0% Control------------------------------
Par Ix + Ben Ix fb
IM Ix 92 99 94 97 99 92
Check 0 0 0 0 0 0
LSD' 10.3 9.2 10.7 5.8 8.3 16.7

a CASOB Senna obtusifolia CYPRO Cyperus rotundus INDHI Indigofera hirsute DEDTO -
Desmodium tortuosum PHYAN Physalis angulata COMBA Commelina banghalensis
bDS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
c All treatments including the check received pendimethalin PPI @ 1120g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.









Table 2.9-Weed control as affected by reduced rate herbicide treatments in 2003 at Jay,
FL in single row study
Late Season"
TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL
-----------------------------% Control ----------------------------------
DS 1/4x 30 78 77 87 96
DS 1/2x 43 86 94 99 99
DS lx 65 99 89 94 99
DS1/4x fb IM 1/4x 52 85 64 96 94
DS 1/4x fb IM 1/2x 68 99 93 99 99
DS 1/2x fb IM 1/4x 48 94 78 99 99
DS 1/2x fb IM 1/2x 59 99 93 99 99
DS 1/2x fb IM lx 75 99 99 99 99
DS lx fb IM lx 85 99 88 99 99
Check 0 0 0 0 0
FL 1/4x 51 62 89 86 89
FL 1/2x 63 76 90 90 90
FL lx 94 67 85 96 91
FL 1/4x fb IM 1/4x 55 94 93 99 96
FL 1/4x fb IM 1/2x 68 96 99 99 99
FL 1/2x fb IM 1/4x 62 81 99 99 99
FL 1/2x fb IM 1/2x 76 99 91 99 99
FL 1/2x fb IM lx 73 99 94 99 96
FL lx fb IM Ix 89 99 99 99 99
DS 1/4x + FL 1/4x 40 95 99 94 94
DS 1/4x + FL 1/4x fb
IM 1/4x 61 90 99 93 96
DS 1/4x + FL 1/4x fb
IM 1/2x 61 99 99 96 99
DS 1/4x + Fl 1/4x fb
IM 2/3x 63 99 99 99 99
DS 1/4x + FL 1/4x fb
IM lx 66 99 99 99 99
DS 1/2x + FL 1/2x fb
IM 1/2x 69 99 99 99 99
DS lx+FL Ixfb










Table 2.9 Continued
Late Season"
TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL
-----------------------------% Control-----------------------------
IM Ix 89 99 99 99 99
IM 1/4x 47 96 75 99 69
IM 1/2x 67 94 73 99 88
Par Ix + Ben Ix fb
IM Ix 96 99 99 99 99
Check 0 0 0 0 0
LSD' 18.3 10.9 15.2 5 8

a CASOB Senna obtusifolia, CYPRO Cyperus rotundus, DEDTO Desmodium tortuosum, IAQTA -
Jaquemontia tamnifolia, EPHHL Euphorbia heterophylla
b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
c All treatments including the check received pendimethalin PPI @ 1120g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.









Table 2.10-Weed control as affected by reduced rate herbicide treatments in 2003 at Jay,
FL in twin row study
Late Season"
TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL
-----------------------------% Control--------------------------------
DS 1/4x 51 88 77 99 94
DS 1/2x 43 99 94 99 99
DS lx 45 96 84 99 96
DS1/4x fb IM 1/4x 50 99 88 99 96
DS 1/4x fb IM 1/2x 79 99 94 99 99
DS 1/2x fb IM 1/4x 60 99 99 99 99
DS 1/2x fb IM 1/2x 66 99 99 99 96
DS 1/2x fb IM lx 77 99 94 99 96
DS lx fb IM lx 73 96 75 99 88
Check 0 0 0 0 0
FL 1/4x 58 84 99 99 96
FL 1/2x 53 90 99 99 96
FL lx 56 94 93 99 96
FL 1/4x fb IM 1/4x 53 93 99 99 96
FL 1/4x fb IM 1/2x 71 99 94 99 99
FL 1/2x fb IM 1/4x 62 94 85 99 99
FL 1/2x fb IM 1/2x 75 99 99 99 96
FL 1/2x fb IM lx 77 99 99 99 99
FL lx fb IM Ix 94 99 99 99 99
DS 1/4x + FL 1/4x 27 74 91 99 96
DS 1/4x + FL 1/4x fb
IM 1/4x 82 99 99 99 96
DS 1/4x + FL 1/4x fb
IM 1/2x 56 99 99 99 99
DS 1/4x + Fl 1/4x fb
IM 2/3x 74 99 99 99 99
DS 1/4x + FL 1/4x fb
IM lx 73 99 94 99 99
DS 1/2x + FL 1/2x fb
IM 1/2x 65 99 99 99 99
DS lx+FL Ixfb
IM lx 94 99 99 99 99
IM 1/4x 53 99 80 99 96
IM 1/2x 67 99 90 99 89










Table 2.10 Continued
Late Seasona
TRT b,c,d CASOB CYPRO DEDTO IAQTA EPHHL
-----------------------------% Control-----------------------------
Par Ix + Ben Ix fb
IM Ix 94 99 99 99 99
Check 0 0 0 0 0
LSDe 19 13 12 0 6

a CASOB Senna obtusifolia, CYPRO Cyperus rotundus, DEDTO Desmodium tortuosum, IAQTA -
Jaquemontia tamnifolia, EPHHL Euphorbia heterophylla
b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
c All treatments including the check received pendimethalin PPI @ 1120g ai/ha
d"+" = tank mix, "fb" = followed by in a sequential treatment
e Fisher's Protected LSD test P < 0.1.










Table 2.11 -Peanut yield
Citra, FL.


as affected by reduced herbicide treatments in 2002 at Jay and


Treatment a,b,c Jay Citra


Check
DS 1/4x

DS Ix

FL 1/4x

FL Ix

DS + FL1/4x

DS+FL 1/4x fb
IM 1/2x
DS+FL 1/4x fb
IM 2/3x
DS Ix fb IM Ix

FL Ix fb IM Ix

DS+FL 1/4x fb
IM Ix
Par+Ben fb
IM Ix


-------------------kg/ha---------------
2529 2571
3056 4003


2617

1992

3574

2882

3525

2412

2812

2763

2480

3242

Aee


4329

3206

4101

4459

3987

4329

3548

3971

3792

N/Ad

VC


aDS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
b All treatments including the check received pendimethalin PPI a 1120g ai/ha
C"+" = tank mix, "fb" = followed by in a sequential treatment
d Regional standard treatment was not included at Citra, Fl.
eP< 0.1 level.










Table 2.12-Peanut yield
FL.
Treatment


as affected by reduced herbicide treatments in 2002 at Marianna,


Marinn;n


DS 1/4x fb IM 1/4x
DS 1/4x fb IM 1/2x
DS 1/2x fb IM 1/4x
DS 1/2x fb IM 1/2x
FL 1/4x fb IMl/4x
FL 1/4x fb IM 1/2x

FL 1/2x fb IM 1/4x

FL 1/2x fb IM 1/2x
DS +FL 1/4x fb
IM 1/4x
DS + FL 1/2x
IM 1/2x
DS + FL 1/2x fb
IM 1/2x
Check


kg/ha
4780
4333
4434
4048
4699
4902

4679

4597
4953

4506

4658

3885
NS d


aDS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
b All treatments including the check received pendimethalin PPI @ 1120g ai/ha
e"+" = tank mix, "fb" = followed by in a sequential treatment
P < 0.1 level.









Table 2.13-Peanut yield as affected by reduced rate herbicide treatments in 2003 at Jay
and Citra, Fl. in twin and single row studies.
Citra Jay
Treatment "' Single Twin Single Twin


DS 1/4x
DS 1/2x
DS Ix
DS 1/4xfbIM 1/4x
DS 1/4x fb IM 1/2x
DS 1/2x fb IM 1/4x
DS 1/2x fb IM 1/2x
DS 1/2x fb IM Ix
DS Ix fb IM Ix
Check
FL 1/4x
FL 1/2x
FL Ix
FL 1/4x fb IM 1/4x
FL 1/4x fb IM 1/2x
FL 1/2x fb IM 1/4x
FL 1/2x fb IM 1/2x
FL 1/2x fb IM Ix
FL Ix fb IM Ix
DS 1/4x +FL 1/4x
DS 1/4x + FL 1/4x fb
IM 1/4x
DS 1/4x + FL 1/4x fb
IM 1/2x
DS 1/4x + Fl 1/4x fb
IM2/3x
DS 1/4x + FL 1/4x fb
IM Ix
DS 1/2x + FL 1/2x fb
IM 1/2x


------------------------------kg/ha---- ---------------
5956 5151 3700 4189
5566 5590 3574 4023
5859 4809 3886 4081
6005 5444 3818 4267
5858 5664 4052 4492
6322 5150 4374 3544
5761 5492 4032 4384
6225 5517 4140 4433
6420 5077 4091 3798
5126 5444 3691 3642
5468 6152 3779 3974
6030 5761 4296 3613
6591 5834 4443 4257
4931 5200 3866 4374
5419 5285 4735 4081
5785 5200 4198 4379
6127 4150 4198 4042
6371 5224 4706 4433
6103 4199 4160 4276
6213 5834 4140 3730


6152

5663

4760

6713


5346

4565

4882

4955


4550

4160

4169

4013


4306

4023

4306

4589


6811 5932


4824 4423










Table 2.13 Continued
Citra Jay
Treatment "JU, Single Twin Single Twin
-------------------------kg/ha----------------kg/ha------
DS Ix+FL Ixfb
IM Ix 6591 5834 3944 4384
IM 1/4x 6225 6298 4657 3984
IM 1/2x 5590 5834 4062 4072
Par Ix + Ben Ix fb
IM Ix 6396 5492 4277 4404
Check 5395 5932 3837 3544
NS d NS NS NS

aDS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
b All treatments including the check received pendimethalin PPI @ 1120g ai/ha
e"+" = tank mix, "fb" = followed by in a sequential treatment
P < 0.1 level.









Table 2.14 Total revenue per treatment as affected by yield and treatment cost separated
by location and row spacing-2003
Citra, FL Jay, FL
Treatment b,c,d Single Twin Single Twin


DS 1/4x
DS 1/2x
DS Ix
DS1/4x fb IM 1/4x
DS 1/4x fb IM 1/2x
DS 1/2x fb IM 1/4x
DS 1/2x fb IM 1/2x
DS 1/2x fb IM Ix
DS Ix fb IM Ix
Check
FL 1/4x
FL 1/2x
FL Ix
FL 1/4x fb IM 1/4x
FL 1/4x fb IM 1/2x
FL 1/2x fb IM 1/4x
FL 1/2x fb IM 1/2x
FL 1/2x fb IM Ix
FL Ix fb IM Ix
DS 1/4x + FL 1/4x
DS 1/4x + FL 1/4x fb
IM 1/4x
DS 1/4x + FL 1/4x fb
IM 1/2x
DS 1/4x + Fl 1/4x fb
IM2/3x
DS 1/4x + FL 1/4x fb
IM Ix
DS 1/2x + FL 1/2x fb
IM 1/2x
DS lx+FL Ixfb
IM Ix
IM 1/4x


------------------------TR ($/hectare).------------------------
1601 1197 470 715
1395 1407 397 622
1522 996 533 631
1613 1332 517 742
1529 1431 624 844
1762 1175 786 370
1470 1335 604 780
1682 1327 637 784
1760 1087 593 446
1210 1369 491 467
1358 1701 512 610
1632 1497 763 421
1898 1519 822 729
1077 1212 544 798
1311 1244 968 640
1498 1205 702 793
1658 668 692 613
1759 1185 925 788
1610 656 636 695
1722 1532 683 477


1679

1423

961

1929

1981

1815
1733


1275


876

670


1022

1048

1541

1436
1770


602


864


576

986

489
947


709
610










Table 2.14 Continued
Citra, FL Jay, FL
Treatment b,c,d Single Twin Single Twin
-------------------TR-------($/hectare).-------------------------
IM 1/2x 1404 1526 639 644
Par lx + Ben Ix fb
IM Ix 1770 1317 709 772
Check 1345 1614 564 417

a Total revenue based on equation: yield per treatment at $0.50 per kg total production cost ($1358 per
hectare) herbicide treatment cost per hectare.
b DS=diclosulam, FL=flumioxazin, IM=imazapic, 1/4x=6.72, 26.3, 17.1g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
c All treatments including the check received pendimethalin PPI @ 1120g ai/ha
d +" = tank mix, "fb" = followed by in a sequential treatment









Table 2.15 Herbicide treatment cost for reduced rate study-2003
Treatment a,


DS 1/4x
DS 1/2x
DS Ix
DS1/4x fb IM 1/4x
DS 1/4x fb IM 1/2x
DS 1/2x fb IM 1/4x
DS 1/2x fb IM 1/2x
DS 1/2x fb IM Ix
DS Ix fb IM Ix
FL 1/4x
FL 1/2x
FL Ix
FL 1/4x fb IM 1/4x
FL 1/4x fb IM 1/2x
FL 1/2x fb IM 1/4x
FL 1/2x fb IM 1/2x
FL 1/2x fb IM Ix
FL Ix fb IM Ix
DS 1/4x + FL 1/4x
DS 1/4x + FL 1/4x fb
IM 1/4x
DS 1/4x + FL 1/4x fb
IM 1/2x
DS 1/4x + Fl 1/4x fb
IM 2/3x
DS 1/4x + FL 1/4x fb
IM Ix
DS 1/2x + FL 1/2x fb
IM 1/2x
DS lx+FL Ixfb
IM Ix
IM 1/4x
IM 1/2x
Par Ix + Ben Ix fb


$/hectare
25.68
35.56
55.31
37.5
48.34
47.38
58.22
79.21
98.96
23.34
30.89
45.97
35.16
46
42.71
53.55
74.75
89.62
33.22

45.04

55.88

66.03

76.87

73.31

129.13
27.62
38.47


IM lx 76.12
" S=diclosulam, IL=flunmoxazmn, IM=imazapic, 1/4x=6.72, 26.3, 17. g ai/ha, 1/2x=13.4, 52.6, 35.3g
ai/ha, lx=26.8, 105.3, 70.6g ai/ha. respectively.
b +" = tank mix, "fb" = followed by in a sequential treatment














CHAPTER 3
EFFECTS OF REDUCED COST HERBICIDE TREATMENT COMBINATIONS ON
WEED MANAGEMENT IN PEANUT (ARACHIS HYPOGAEA L.) PRODUCTION

Introduction

In 2002, approximately 3.19 million hectares of peanut (Arachis hypogaea L.) were

harvested in the United States with an average yield of 2,870 kilograms per hectare

(USDA 2002). This was a 5% reduction from 2001 and a 4% reduction from 2000.

Growers in the Southwest (New Mexico, Oklahoma, and Texas) planted 180,000 hectares

of peanut in 2001, 16% less than 2000. Plantings in the Virgina-North Carolina region

totaled 67,000 hectares, a 17% reduction from 2001. Peanut planting in these areas was

delayed due to the early dry conditions and peanut hectarage was reduced in response to

the new Farm Bill, growers planted fewer dry-land peanut because they often have a

lower yield potential than irrigated peanut.

The Southeast (Alabama, Florida, Georgia, and South Carolina) is the largest

production region of peanut in the United States with over 350,000 hectares planted in

2002, an increase of 6% from 2001 (USDA 2002). Peanut are a significant part of the

row crop economy in Florida. Florida is ranked 5th nationally in production and Jackson

County is the 3rd leading peanut producing county in the United States. In 2002, Florida

harvested 35,000 hectares with an average yield of 2,600 kilograms per hectare (Aerts

and Nesheim 2000).

Since 1990 the price per kilogram received for peanut has declined considerably

from $ 0.66/kg to the December 2001 price of $0.43/kg. The 2002 Farm Bill will be the









determining factor for profitability of peanut. Growers were receiving the previous quota

price of $0.67/kg but that has been reduced to $0.39/kg as a result of the 2002 Farm Bill.

Pest management accounts for a large portion of the variable production cost for

peanut. More than 36% of the total operating costs are invested in pesticides (Aerts and

Nesheim 2000). In peanut, there are over 43 weed species, 20 insect pests, 17 disease

and 4 nematode pathogens that are of economic importance in 9 peanut producing states.

The worst weed pests, if left uncontrolled, can reduce yield 30-80 percent in infested

areas (Aerts and Nesheim 2000).

Peanut weed control is accomplished through cultural, mechanical, and chemical

practices. Crop rotation has many benefits, including better weed control that is obtained

when a variety of herbicides are used. Mixing two herbicides with different modes of

action reduces the probability of weed resistance and shifts. Cultivation may be utilized

if effective weed control with herbicides is not achieved (Ducar et al. 2002).

In peanut, the most effective weed control and highest yield has generally been

obtained using a herbicide program that includes a preplant incorporated (PPI) and/or

preemergence (PRE) treatment, followed by an at cracking (AC) stage treatment,

followed by a postemergence (POST) application (Ducar et al. 2002). Traditional

herbicide applications have included pendimethalin or ethalfluralin applied PPI for

control of annual grasses and small seeded broadleaf weeds followed by a PRE

application of diclosulam, flumioxazin, or norflurazon for additional control of broadleaf

weeds. At cracking and POST herbicides most commonly used in Florida peanut

production include: paraquat for broad spectrum early season weed control; bentazon for

control of yellow nutsedge (Cyperus esculentus L.) and good control of various broadleaf









weeds; 2,4-DB for control of momingglory spp. (Ipomoea spp.) and sicklepod (Senna

obtusifolia L.); chlorimuron or imazapic for late season Florida beggarweed (Desmodium

tortuosum (sweet) DC.), nutsedge, and multiple broadleaf weed species control (Ducar et

al. 2002).

Traditional herbicide programs use as many as five or six herbicides applied at the

full labeled rate. With the reduction of revenue due to the new Farm Bill, farmers will

need new tactics to reduce their production cost possibly by configuring herbicide

treatment combinations that will reduce the cost. The objective of this research was to

determine the economic effectiveness of reduced cost (either by eliminating some

herbicide treatments or reducing herbicide rates) herbicide programs.

Materials and Methods

Field studies were conducted in 2002 and 2003 at the West Florida Research and

Education Center near Jay, FL, and in 2003 at the North Florida Research and Education

Center near Marianna, FL, and at the Plant Science Research and Education Center near

Citra, FL. Jay is located in the far West panhandle of Florida with soil type of Red Bay

sand loam (fine-loamy, siliceous, thermic, Rhodic paleudults) at pH 5.8 and organic

matter of 2.1%. Marianna is located in the central panhandle with Chipola loamy sand

(loamy, siliceous, thermic Arenic Hapudult) soil type containing 1.0% organic matter and

pH of 6.2. Citra is located in North Central Florida with soil type Sparr sand (loamy,

siliceous, hyperthermic, Grossa-renic paleudult) with organic matter 1% and pH of 6.4.

Conventional tillage system consisting of a deep moldboard plowing, leveling

disking and one field cultivation prior to planting was used to prepare the field for peanut

planting.









The peanut variety C-99R was planted on May 7, 2002 at Jay, FL and April 30,

May 5 and May 13, 2003 at Citra, Jay, and Marianna, FL respectively. Peanuts were

planted at a depth of 6 cm and seeding rate of 122 kg/ha. Row spacing was 91 cm single

rows in 2002 and 2003 at all three locations. Plots at Citra were four row (3.0m) wide

and 6.1 m long. Plots at Jay and Marianna were four row (3.0m) wide and (7.0m) long.

A randomized complete block was utilized as the experimental design to arrange the

herbicide treatments.

Soil fertilization and liming practices were in accordance with test

recommendations by the University of Florida Soil Testing Laboratory. Florida

Cooperative Extension Service recommendations were followed for management of

fungicide, insecticide, and irrigation.

Herbicide treatments and application rates are listed in tables 3.1 and 3.2 and

consist of 9 commonly used herbicides in peanut production applied in various programs

ranging in cost from $5 to $66 per hectare (Table 3.9, 3.10). All AC, early post

(EPOST), or POST applications also included a non-ionic surfactant (Induce) of 0.25 %

V/V. Herbicides were applied with a CO2 pressurized backpack sprayer calibrated to

deliver 187 L/ha.

Weed control was visually evaluated using a scale of 0 (no control) to 100

(complete control) early, -35 days after planting (DAP), and late, -120 DAP, during the

growing season.

The center two rows from each plot were harvested using conventional equipment

approximately 140-148 DAP at physiological maturity as determined by the hull scrape

method (Johnson 1987). Plot yields were converted to yield per hectare at 8% moisture.









Economic return was determined for each treatment based on yield per hectare

utilizing the following formula:

Yield/hectare @ $0.501 per kg $1358/ha (total production cost) herbicide cost/ha

The price per ton and total production cost was based on the average Florida peanut

grower as determined through conversation with University of Florida's Extension

Agriculture Economist. Herbicide prices used in the analysis were obtained from several

farm supply stores throughout Florida's peanut production region.

SAS (1996) Proc GLM software was used to analyze the data. Data were subjected

to analysis of variance to test treatment effects an interactions. Means were separated

using Fisher's Protected LSD Test at the p<0.1 level.

Results and Discussion

Treatments in 2002 were different from 2003 and location interactions for all

parameters measured prevented pooling of data. Therefore, data is presented separately

for each location and year.

Weed Control-2002

Predominant weeds at Jay in 2002 were common cocklebur (Xanthium strumarium

L), sicklepod (Senna obtusifolia L.), Florida pusley (Richardia scabra L.), and yellow

nutsedge (Cyperus esculentus L.). Pendimethalin PPI fb imazapic at 3/4x and 2,4-DB

POST provided greater than 87% late season control over all weeds evaluated (Table

3.3). Using imazapic at 1/2x with pendimethalin and 2,4-DB provided comparable weed

control for a treatment cost $10/ha less. Pendimethalin fb either imazapic at full rate or

2,4-DB provided greater than 80% control over all weeds evaluated. Metolachlor and

paraquat used AC fb 2,4-DB (a treatment without imazapic) also provided greater than

84% control over all weeds in the study.









Weed Control-2003

Predominant weeds at Jay in 2003 were Florida beggarweed (Desmodium

tortuosum (Sw) DC.), smallflower momingglory (Jaquemontia tamnifolia (L.) Griseb),

sicklepod, Florida pusley, and purple nutsedge (Cyperus rotundus L.). Metolachlor alone

AC only provided control of Florida pusley (87%) and purple nutsedge (89%) (Table

3.4). When paraquat was added AC to metolachlor, control of all weeds evaluated as

>75% and when 2,4-DB was included to this treatment, control provided was >92%.

Treatment with chlorimuron applied 60 DAE and paraquat AC required one treatment of

2,4-DB POST to obtain weed control >83%. Providing weed control greater than 92%

over all weeds evaluated late season were treatments including metolachlor and paraquat

AC and pendimethalin PRE fb imazapic POST or diclosulam PRE and paraquat AC. All

of these three treatments used 2,4-DB POST. Treatments that did not receive a POST

application of imazapic or 2,4-DB provided inadequate weed control over all weeds

evaluated.

Predominant weeds at Citra in 2003 were Florida beggarweed, pigweed

(Amaranthus spp.), tropical spiderwort (Commelina benghalensis L), crowfootgrass

(Dactyloctenium aegyptium L.), and purple nutsedge. Tropical spiderwort was controlled

83 to 99% by all treatments except pendimethalin PPI alone, mainly due to the low

populations of approximately 2 to 4 plants/m2 (Table 3.5). Treatments that did not utilize

pendimethalin PPI controlled crowfootgrass less than 79%. When crowfootgrass was not

controlled, it dominated the plot, reduced populations of other species, and interfered

with harvesting (Table 3.7). Herbicide treatments which included pendimethalin PPI fb

imazapic at Ix or 3/4x POST, imazapic plus 2,4-DB POST, diclosulam PRE fb paraquat

AC fb 2,4-DB POST, and diclosualm at 1/2x PRE fb imazapic at 1/2x POST provided









greater than 92% control over all weeds evaluated. Purple nutsedge control was higher in

treatments using diclosulam (92%) compared to treatments using flumioxazin (80%)

when both herbicides were followed by the same POST application.

Predominant weeds at Marianna were crowfootgrass, sicklepod, smallflower

morningglory, yellow nutsedge, and tropic croton (Croton glandulosus L.). Sicklepod

was present in low populations and sporadic throughout the location. Similar to Citra,

treatments that did not utilize pendimethalin PPI provided less than 74% control of

crowfootgrass (Table 3.6). Pendimethalin PPI fb imazapic plus 2,4-DB POST,

diclosulam PRE fb paraquat AC, or diclosulam at 1/2x PRE fb imazapic at 1/2x POST

provided greater than 89% control over all weeds evaluated. Treatments using

pendimethalin PPI fb imazapic at 1/2x plus 2,4-DB POST provided greater than 94%

control of all weeds except sicklepod (84%). Providing greater than 90% control of all

weeds except yellow nutsedge (78%) the program using pendimethalin PPI fb diclosulam

at 1/2x PRE fb paraquat AC fb 2,4-DB POST. Yellow nutsedge populations were high at

Marianna and pendimethalin alone provided the poorest control. Control was higher in

treatments using diclosulam at Ix (81%) compared to treatments using flumioxazin at Ix

(68%) when both herbicides were followed by the same POST application. All other

weeds evaluated were controlled greater than 88% by these treatments.

Peanut Yield

There were no significant differences among yield treatments at Jay in 2002.

Yields were low and variable across the study site (Table 3.7). This was likely due to a

combination of a late-season infestation of Cylindrocladium black rot (CBR) and heavy

rains from a tropical storm that delayed drying and harvesting after digging and inverting

was complete. Treatments of metolachlor and pendimethalin application alone ant the









non-treated check yielded the least. Highest yielding were metolachlor and paraquat AC,

paraquat and 2,4-DB AC fb chlorimuron and 2,4-DB 60 DAE, and pendimethalin PPI fb

diclosulam at 1/2x fb paraquat AC fb 2,4-DB POST (1943, 1923, and 2079 kg/ha,

respectively). Sicklepod was the only weed that was controlled <83 % in these

treatments.

There was no significant difference among treatments at Jay and Citra, FL in 2003.

At Jay, pendimethalin PPI fb imazapic POST was the highest yielding treatment (4609

kg/ha) (Table 3.8). Yielding the lowest was metolachlor applied AC alone (3505 kg/ha).

At Citra, yield was generally higher and pendimethalin PPI fb imazapic and 2,4-DB

POST was the highest yielding treatment (6616 kg/ha). Lower yield was observed with

paraquat applied AC alone (2734 kg/ha). Crowfootgrass was an abundant weed at Citra

and in treatments without pendimethalin yield was lower (2734, 3784, 3033 and 3613

kg/ha).

At Marianna in 2003, treatments with pendimethalin PPI fb imazapic 1/2x POST,

pendimethalin PPI fb imazapic 1/2x mixed with 2,4-DB POST, and pendimethalin PPI fb

diclosulam 1/2x PRE fb paraquat AC, fb 2,4-DB POST were the highest yielding (4374,

4511, and 4394 kg/ha, respectively). Treatments using pendimethalin PPI fb paraquat

AC and paraquat AC fb chlorimuron and 2,4-DB 60DAE, or fb 2,4-DB POST fb

chlorimuron and 2,4-DB 60 DAE were the lowest yielding (2851, 2949, 2539 kg/ha,

respectively). This was a result of the <37% control of crowfootgrass in the treatments

without pendimethalin PPI. Pendimethalin fb paraquat was unable to adequately control

smallflower morningglory and yellow nutsedge <79% resulting in lower yield.









Economic Analysis

Total revenue at Jay in 2002 were all negative values because of the low yield

received per treatment. Treatment using pendimethalin PPI fb diclosulam at 1/2x PRE fb

paraquat AC fb 2,4-DB POST provided the highest total revenue ($-362.63/ha) with

treatment cost of $46.42/ha (Table 3.9 & 3.11).

Jay in 2003 did show positive economic returns. Highest total revenue was

obtained using pendimethalin PPI fb imazapic at 3/4x POST ($902.19/ha) with treatment

cost of $49.38/ha (Table 3.10 and 3.12). Next highest return was realized from the

program of pendimethalin PPI fb imazapic at Ix POST ($769.54/ha) costing $59.26/ha.

Metolachlor applied PRE only was the lowest total revenue ($363.79/ha) with treatment

cost of $14.00/ha.

The highest total revenue at Citra was from the treatment pendimethalin PPI fb

imazapic and 2,4-DB POST and next highest was from pendimethalin PPI fb imazapic at

1/2x ($1893.09 and $1673.72/ha) with treatment cost of $64.20 and $38.52/ha

respectively. The lowest total revenue was earned with paraquat AC alone ($7.07/ha) at

treatment cost of $2.00/ha.

Highest total revenue at Marianna was achieved using pendimethalin PPI fb

imazapic at 1/2x and 2,4-DB POST ($858.02/ha) with treatment cost of $44.44/ha. Next

highest total revenue used pendimethalin PPI fb diclosulam at 1/2x PRE fb paraquat AC

fb 2,4-DB POST ($797.41/ha) with treatment cost of $46.42/ha. Paraquat AC fb 2,4-DB

POST fb chlorimuron and 2,4-DB 60DAE received the lowest total revenue ($-

118.30/ha) due to grass control less than 37% with treatment cost of $13.20/ha.

Results indicate that with regional standard herbicide treatments averaging $76/ha,

adequate weed control and a net profit higher than the standard can be achieved with









reduced cost herbicide treatments. Systems which used pendimethalin PPI followed by

imazapic and/or 2,4-DB POST consistently, from the three locations, resulted in the

highest total revenue earned costing less than the regional standard herbicide treatment.

Since the passing of the 2002 Farm Bill, growers are now having to compete in a global

market receiving the world price per ton for their peanut which is significantly lower than

the price previously available. Peanut is a high management, high input crop with the

cost of inputs steadily increasing. To remain competitive, growers must find ways in

which to improve production efficiency. Using reduced cost combinations of herbicides

applied without compromising yield and provide adequate weed control is one way to

reduce the 40% of total production cost that results from pesticides (Aerts and Nesheim

2000).









Table 3.1-2002 Reduced Cost Herbicide Treatments
Abbreviation a Treatmentb

Check NONTREATED
Pen pendimethalin
Par paraquat
Par+ben paraquat +
bentazon

Pen+par pendimethalin fb
paraquat


Pen+par+ben

Met*
Met+par


Met+par*


Met+par+DB


Par+chl


Par+chl+DB


Par+2,4+chl+
DB


Pen+im


Pen+im+DB


pendimethalin fb
paraquat + bentazon
metolachlor
metolachlor +
paraquat

metolachlor +
paraquat

metolachlor +
paraquat fb
2,4-DB


paraquat fb
chlorimuron

paraquat fb
2,4-DB fb
chlorimuron

paraquat fb
2,4-DB fb
chlorimuron fb
2,4-DB

Pendimethalin fb
imazapic

pendimethalin fb
imazapic +
2,4-DB


Rate
g ai/ha

1120
140
140 +
280

1120 +
140


1120 +
140 + 280
1400
1400 +
140

1400 +
140

1400 +
140 +
280


140 +
9

140 +
280 +
9

140 +
280 +
9+
280

1120 +
70.6

1120 +
70.6 +
280


Timing


PRE
AC
AC+
AC

PRE fb
AC

PRE fb
AC
AC
AC +
AC

AC+
AC

AC+
AC fb
POST

AC fb
60 DAE

AC fb
POST fb
60 DAE

AC fb
POST fb
60 DAE +
60 DAE


PRE fb
POST

PRE fb
POST +
POST









Table 3.1 Continued
Abbreviation a

Pen+im3/4


Pen+iml/2


Pen+im3/4+
DB


Pen+im 1/2+
DB


Pen+fl+par



Pen+fl+par+
DB



Pen+fl 1/2+
Par+DB



Pen+ds+par



Pen+ds+par
+DB


Treatment b

pendimethalin fb
imazapic 3/4x

pendimethalin fb
imazapic 1/2x

pendimethalin fb
imazapic 3/4x +
2,4-DB

pendimethalin fb
imazapic 1/2x +
2,4-DB

pendimethalin fb
flumioxazin fb
paraquat

pendimethalin fb
flumioxazin fb
paraquat fb
2,4-DB

pendimethalin fb
flumioxazin 1/2x fb
paraquat fb
2,4-DB

pendimethalin fb
diclosulam fb
paraquat

pendimethalin fb
diclosulam fb
paraquat fb
2,4-DB


Pen+dsl/2+par pendimethalin fb 1120+ PRE +
+DB diclosulam 1/2x fb 13.4 + PRE fb
paraquat fb 140+ AC fb
2,4-DB 280 POST
a Treatments did not include a surfactant. All other treatments received a surfactant of 0.25% V/V at AC,
EPOST, POST, and 60DAE applications
b "+" = tank mix, "fb" = followed by in a sequential treatment


Rate
g ai/ha
1120 +
46.6

1120 +
35.3

1120 +
46.6 +
280

1120 +
35.3 +
280

1120 +
105.3 +
140

1120 +
105.3 +
140+
280

1120+
52.6+
140+
280

1120+
26.8+
140

1120+
26.8+
140+
280


Timingb

PRE fb
POST

PRE fb
POST

PRE fb
POST +
POST

PRE fb
POST +
POST

PRE +
PRE fb
AC

PRE +
PRE fb
AC fb
POST

PRE +
PRE fb
AC fb
POST

PRE +
PRE fb
AC

PRE +
PRE fb
AC fb
POST









Table 3.2-2003 Reduce Cost Herbicide Treatments
Abbreviation" Treatmentb


Check
Pen
Par
Par+ben


Pen+par

Pen+par+ben

Met*
Met+par


Met+par+DB



Par+chl


Par+chl+DB


Par+DB+chl+
DB


Pen+im


Pen+im+DB


Pen+im3/4

Pen+im 1/2


Pen+im3/4+
DB


NONTREATED
pendimethalin
paraquat
paraquat +
bentazon
pendimethalin fb
paraquat
pendimethalin fb
paraquat + bentazon
metolachlor
metolachlor +
paraquat

metolachlor +
paraquat fb
2,4-DB

paraquat fb
chlorimuron

paraquat fb
2,4-DB fb
chlorimuron

paraquat fb
2,4-DB fb
chlorimuron fb
2,4-DB

Pendimethalin fb
imazapic

pendimethalin fb
imazapic
2,4-DB

pendimethalin fb
imazapic 3/4x
pendimethalin fb
imazapic 1/2x

pendimethalin fb
imazapic 3/4x +


Rate
g ai/ha

1120
140
140 +
280
1120 +
140
1120 +
140 + 280
1400
1400 +
140

1400 +
140
280

140 +
9

140 +
280 +
9


140 +
280 +
9+
280

1120 +
70.6

1120 +
70.6 +
280

1120 +
46.6
1120 +
35.3

1120 +
46.6 +


Timingb


PRE
AC
AC +
AC
PRE fb
AC
PRE fb
AC
AC
AC +
AC

AC +
AC fb
POST

AC fb
60 DAE

AC fb
POST fb
60 DAE

AC fb
POST fb
60 DAE +
60 DAE

PRE fb
POST

PRE fb
POST +
POST

PRE fb
POST
PRE fb
POST

PRE fb
POST +









Table 3.2 Continued
Abbreviation"


Treatment b


2,4-DB


Pen+im 1/2+
DB


Pen+fl+par



Pen+fl+par+
DB



Pen+fl 1/2+
Par+DB



Pen+ds+par



Pen+ds+par
+DB



Pen+dsl/2+par
+DB



Pen+fll/2x+iml/2x


pendimethalin fb
imazapic 1/2x +
2,4-DB

pendimethalin fb
flumioxazin fb
paraquat

pendimethalin fb
flumioxazin fb
paraquat fb
2,4-DB

pendimethalin fb
flumioxazin 1/2x fb
paraquat fb
2,4-DB

pendimethalin fb
diclosulam fb
paraquat

pendimethalin fb
diclosulam fb
paraquat fb
2,4-DB

pendimethalin fb
diclosulam 1/2x fb
paraquat fb
2,4-DB

pendimethalin +
flumioxazin 1/2x fb
imazapic 1/2x


Pen+dsl/2x+iml/2x pendimethalin + 1120+ PRE +
diclosulam 12X fb 13.4 + PRE fb
imazapic 1/2x 35.3 POST
a Treatments did not include a surfactant. All other treatments received a surfactant of 0.25% V/V at AC,
EPOST, POST, and 60DAE applications
b "+" = tank mix, "fb" = followed by in a sequential treatment


Rate
g ai/ha
280

1120 +
35.3 +
280

1120 +
105.3 +
140

1120 +
105.3 +
140+
280

1120+
52.6+
140+
280

1120+
26.8+
140

1120+
26.8+
140+
280

1120+
13.4 +
140+
280

1120 +
52.6+
35.3


Timingb

POST

PRE fb
POST +
POST

PRE +
PRE fb
AC

PRE +
PRE fb
AC fb
POST

PRE +
PRE fb
AC fb
POST

PRE +
PRE fb
AC

PRE +
PRE fb
AC fb
POST

PRE +
PRE fb
AC fb
POST

PRE +
PRE fb
POST










Table 3.3-Weed control with reduced cost herbicide treatments in 2002 at Jay, FL.
Late Season


Treatment I


Pen
Par
Par+ben
Pen+par
Pen+par+ben
Met*
Met+par
Met+par*
Met+par+DB*
Par+chl
Par+chl+DB
Par+DB+chl+
DB
Pen+im
Pen+im+DB
Pen+im3/4
Pen+im 1/2
Pen+im3/4+
DB
Pen+im 1/2+
DB
Pen+fl+par
Pen+fl+par+
DB
Pen+fl 1/2+
Par+DB
Pen+ds+par


87
100
100
100
100

100

97
95

97

97
100


95
97
100
92
100

100

100
95

95

95
95


Pen+ds+par
+DB 97 100 61 81
Pen+dsl/2+par
+DB 100 100 67 83
LSDC 10 14.3 13.1 20.6
a XANST = (Xanthuim strumarium L), CASOB = (Senna *'btn &/)i RCHSC = (Richardia scabra), and
CYPES = (Cyperus esculentus)
bPen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam
a Fisher's Protected LSD test P < 0.1.
Did not received a surfactant of 0.25% V/V. All other AC, POST & 60DAE treatments did


WCHSCa XANST CASOB CYPES
-------------------% Control----------------------
95 17 5 12
72 92 55 52
47 85 61 68
95 86 50 70
95 93 58 72
90 20 0 47
92 80 56 78
100 87 75 85
97 91 84 92
37 85 62 77
77 96 70 82





Pen+ds+par+
DB 89 99 94 99 99
Pen+dsl/2+par
+DB 95 99 94 99 92
Pen+fll/2x+iml/2x 65 96 99 99 90
Pen+dsl/2x+iml/2x 73 99 99 99 99
LSD c 15 13 15 9 9
"DEDTO = Desmodium tortuosum, IAQTA = Jaquemontia tamnifolia, CASOB = Senna obtusifolia,
RCHSC = Richardia scabra, and CYPRO = Cyperus rotundus
b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam
' Fisher's Protected LSD test P < 0.1.


Table 3.4-Weed control with reduced cost herbicide treatments in 2003 at Jay, FL.
Late Season a
Treatment CASOB IAQTA DEDTO RCHSC CYPRO
------------------- ------- control---------% control----------------------------------
Pen 42 62 83 79 73
Par 75 57 96 87 87
Par+ben 73 75 72 61 90
Pen+par 63 71 78 94 82
Pen+par+ben 83 87 94 96 88
Met 45 65 67 87 89
Met+par 77 75 92 93 94
Met+par+DB 94 99 99 99 92
Par+chl 94 67 96 79 84
Par+chl+DB 94 96 99 94 83
Par+DB+chl+
DB 86 99 99 99 89
Pen+im 89 99 99 99 99
Pen+im+DB 96 96 99 99 99
Pen+im3/4 79 99 91 99 99
Pen+im 1l/2 79 99 93 99 96
Pen+im3/4+
DB 84 99 87 99 99
Pen+im 1/2+
DB 92 96 87 99 99
Pen+fl+par 77 88 86 96 91
Pen+fl+par+
DB 96 99 93 99 86
Pen+fl 1/2+
Par+2,4 99 96 96 96 88
Pen+ds+par 74 99 89 99 96










Table 3.5-Weed control with reduced cost herbicide treatments in 2003 at Citra, FL
Late Season a


Treatment

Pen
Par
Par+ben
Pen+par
Pen+par+ben
Met
Met+par
Met+par+DB
Par+chl
Par+chl+DB
Par+DB+chl+
DB
Pen+im
Pen+im+DB
Pen+im3/4
Pen+im 1/2
Pen+im3/4+
DB
Pen+im 1l/2x+
DB
Pen+fl+par
Pen+fl+par+
DB
Pen+fl 1/2+
Par+2,4
Pen+ds+par


DEDTO CYPRO AMASP DTTAE COMBA
------------------------------------% control-----------------------------
92 81 82 76 62
74 77 71 50 94
78 90 74 47 94
95 90 96 92 96
98 81 99 80 96
88 86 89 37 89
95 84 71 52 94
95 94 96 79 95
96 88 91 57 96
98 91 88 42 94


Pen+ds+par+
DB 98 92 99 93 99
Pen+dsl/2+par
+DB 98 92 96 86 95
Pen+fll/2x+iml/2x 98 94 96 87 89
Pen+dsl/2x+iml/2x 98 96 96 92 99
LSD c 13.1 10.8 10.8 17.7 12.2
" DEDTO = Desmodium tortuosum, AMASP = Amaranthus spp., COMBA = Commelina banghalensis,
DTTAE = Dactyloctenium ui I i-', and CYPRO = Cyperus rotundus
b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam
' Fisher's Protected LSD test P < 0.1.





Pen+ds+par
+DB 99 95 96 72 99
Pen+dsl/2+par
+DB 99 90 96 78 99
Pen+fll/2x+iml/2x 99 88 96 88 96
Pen+dsl/2x+iml/2x 99 89 99 99 96
LSDC 13.3 11.6 13.1 12.6 12.9
a DEDTO = Dactyloctenium i., '\ai*-i. CASOB = Senna obtusifolia, IAQTA = Jaquemontia tamnifolia,
CYPES = Cyperus esculentus, and CVNGL = Croton glandulosus
b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam
' Fisher's Protected LSD test P < 0.1.


Table 3.6-Weed control with reduced cost herbicide treatments in 2003 at Marianna, FL
Late Season'
Treatment DTTAE CASOB IAQTA CYPES CVNGL
---------------------------------control----------------------------------
Pen 74 75 57 65 58
Par 35 80 45 86 85
Par+ben 42 77 52 83 83
Pen+par 99 91 56 69 84
Pen+par+ben 96 86 66 77 80
Met 84 89 73 80 72
Met+par 68 90 60 85 82
Met+par+DB 40 94 87 90 93
Par+chl 42 92 58 76 88
Par+chl+DB 35 90 78 88 95
Par+DB+chl
+DB 37 92 89 88 91
Pen+im 99 91 99 98 77
Pen+im+DB 99 91 94 97 98
Pen+im3/4 99 83 88 94 77
Pen+iml/2 99 82 96 96 66
Pen+im3/4
+DB 99 81 84 87 88
Pen+im 1l/2x
+DB 99 84 96 94 95
Pen+fl+par 99 99 81 72 96
Pen+fl+par
+DB 93 96 96 65 99
Pen+fl 1/2
+Par+2,4 96 94 92 67 95
Pen+ds+par 95 94 93 94 92










Table 3.7-Yield with reduced cost herbicide treatments in 2002 at Jav. FL
Treatment"
kg/ha
Check 468
Pen 439
Par 1464
Par+ben 1494
Pen+par 1162
Pen+par+ben 1660
Met 615
Met+par 1631
Met+par 1943
Met+par+2,4 1699
Par+ch 1884
Par+chl+2,4 1660
Par+2,4+chl+2,4 1923
Pen+im 1465
Pen+im+2,4 1367
Pen+im3/4 1464
Pen+iml/2 1640
Pen+im3/4+2,4 1787
Pen+im1/2+2,4 1689
Pen+fl+par 1689
Pen+fl+par+2,4 1513
Pen+fl 1/2+Par+2,4 1786
Pen+ds+par 1562
Pen+ds+par+2,4 1591
Pen+dsl/2+par+2,4 2079
LSDb NS


a Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam
b Fisher's Protected LSD test P < 0.1.










Table 3.8-Yield with reduced cost herbicide treatments in 2003 at Jay, Citra, and
Marianna, FL
Treatmenta Jay Marianna Citra


Check
Pen
Par
Par+ben
Pen+par
Pen+par+ben
Met
Met+par
Met+par+DB
Par+chl
Par+chl+DB
Par+DB+chl+DB
Pen+im
Pen+im+DB
Pen+im3/4
Pen+im 1/2
Pen+im3/4+DB
Pen+im 1/2+DB
Pen+fl+par
Pen+fl+par+DB
Pen+fl 1/2+Par+DB
Pen+ds+par
Pen+ds+par+DB
Pen+ds 1/2+par+DB
Pen+fl 1/2x+iml/2x
Pen+dsl/2x+iml/2x
LSDb


------------gha------
-------------------kg/ha---------------------
3837 4023 3955
3769 3808 5713
3866 4179 2734
4081 3496 4468
3954 2851 5664
4023 3515 4126
3505 3456 3784
4160 3398 3003
3828 3359 3931
3867 3124 3906
3611 2949 3613
4238 2539 4712
4364 3925 4077
3681 3652 6616
4609 3691 4980
3964 4374 6127
4140 3886 4663
4296 4511 5615
4042 3827 5151
4111 3378 4516
4081 3828 5029
3974 3788 4077
4140 3554 5249
4042 4394 5322
3906 3710 4492
3700 4160 5078
NS 934.3 NS


a Pen=pendimethalin, ben=bentazone, chl=
fl=flumioxazin, ds=diclosulam
b Fisher's Protected LSD test P < 0.1.


=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,










Table 3.9-Herbicide treatment cost for reduced cost studv-2002
Treatment"a


Check
Pen
Par
Par+ben
Pen+par
Pen+par+ben
Met
Met+par
Met+par
Met+par+DB
Par+ch
Par+chl+DB
Par+DB+chl+DB
Pen+im
Pen+im+DB
Pen+im3/4
Pen+im 1/2
Pen+im3/4+DB
Pen+im 1/2+DB
Pen+fl+par
Pen+fl+par+DB
Pen+fl 1/2+Par+DB
Pen+ds+par
Pen+ds+par+DB
Pen+ds 1/2+par+DB
a Pen=pendimethalin, ben=bentazone, chl
fl=flumioxazin, ds=diclosulam


$/hectare
0
15.80
4.93
16.79
20.86
32.59
34.56
39.5
38.51
44.44
20.74
26.66
32.59
59.25
65.43
48.64
38.46
54.56
44.44
50.86
56.79
41.97
60.24
66.17
46.41
=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,










Table 3.10-Herbicide treatment cost for reduced cost study-2003
Treatment"a


Check
Pen
Par
Par+ben
Pen+par
Pen+par+ben
Met
Met+par
Met+par+DB
Par+ch
Par+chl+DB
Par+DB+chl+DB
Pen+im
Pen+im+DB
Pen+im3/4
Pen+im 1/2
Pen+im3/4+DB
Pen+im 1/2+DB
Pen+fl+par
Pen+fl+par+DB
Pen+fl 1/2+Par+DB
Pen+ds+par
Pen+ds+par+DB
Pen+ds 1/2+par+DB
Pen+fll/2x+iml/2x
Pen+dsl/2x+iml/2x
a Pen=pendimethalin, ben=bentazone, chl
fl=flumioxazin, ds=diclosulam


$/hectare
0
15.80
4.93
16.79
20.86
32.59
34.56
39.5
44.44
20.74
26.66
32.59
59.25
65.43
48.64
38.46
54.56
44.44
50.86
56.79
41.97
60.24
66.17
46.41
53.58
58.27
=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,










Table 3.11-Total revenue for reduced cost treatments at Jay, FL-2002

Jay, FL.
Treatment Revenuea
($/hectare)
Check -1123.49
Pen -1153.82
Par -629.32
Par+ben -626.14
Pen+par -796.58
Pen+par+ben -558.76
Met -1084.39
Met+par -580.21
Met+par -422.81
Met+par+DB -551.07
Par+ch -434.66
Par+chl+DB -552.84
Par+DB+chl+DB -426.97
Pen+im -683.14
Pen+im+DB -738.42
Pen+im3/4 -673.03
Pen+iml/2 -574.66
Pen+im3/4+DB -517.10
Pen+iml/2+DB -556.08
Pen+fl+par -562.50
Pen+fl+par+DB -656.62
Pen+fll/2+Par+DB -505.01
Pen+ds+par -635.52
Pen+ds+par+DB -626.92
Pen+dsl/2+par+DB -362.63
a Total revenue based on equation: yield per treatment at $0.501 per kg total production cost ($1358 per
hectare) herbicide treatment cost per hectare.
b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam










Table 3.12-Total revenue for reduced cost treatments-2003
Jay, FL Citra, FL Marianna, FL
Treatment Revenuea Revenue Revenue
($ hectare')
Check 564.72 623.85 657.93
Pen 514.84 1588.98 534.39
Par 574.31 7.07 731.16
Par+ben 670.20 864.12 377.06
Pen+par 602.36 1459.24 49.65
Pen+par+ben 625.33 676.95 340.77
Met 363.76 503.59 339.23
Met+par 687.07 107.30 305.23
Met+par+DB 514.78 566.39 279.76
Par+ch 559.01 578.56 186.70
Par+chl+DB 424.31 425.31 92.58
Par+DB+chl+DB 733.07 970.59 -118.30
Pen+im 769.54 625.73 549.56
Pen+im+DB 422.35 1893.08 407.82
Pen+im3/4 902.19 1088.10 442.18
Pen+iml/2 589.84 1673.72 795.29
Pen+im3/4+DB 661.99 924.06 534.71
Pen+iml/2+DB 750.28 1411.23 858.02
Pen+fl+par 616.57 1172.30 508.85
Pen+fl+par+DB 645.23 848.18 277.93
Pen+fll/2+Par+DB 645.01 1120.06 518.24
Pen+ds+par 573.12 624.74 479.92
Pen+ds+par+DB 650.38 1206.10 356.74
Pen+ds 1/2+par+DB 621.03 1262.43 797.41
Pen+fll/2x+iml/2x 545.72 839.36 447.50
Pen+dsl/2x+iml/2x 437.80 1128.31 668.30

a Total revenue based on equation: yield per treatment at $455 per ton total production cost ($550 per
hectare) herbicide treatment cost per hectare.
b Pen=pendimethalin, ben=bentazone, chl=chlorimuron, DB=2,4-DB, im=imazapic, par-paraquat,
fl=flumioxazin, ds=diclosulam















CHAPTER 4
PEANUT (ARACHIS HYPOGAEA L.) VARIETY RESPONSE TO SELECTED
HERBICIDES

Introduction

Differential response to herbicides is common in peanut (Jordan et al. 1998). These

responses can include phytotoxic symptoms and/or a reduction in growth or yield. It is

important to test new varieties they are released to determine tolerance to commonly used

herbicides.

Results from earlier studies show 'Early Bunch', a Virginia market type peanut,

exhibited early-season injury from naptalam plus dinoseb and paraquat applied early post

emergence (Brecke 1989). Imazapic injured 'Florunner', 'Georgia Runner', 'GK 7', 'NC 7',

'NC-V11', 'Southern Runner', 'Sunrunner', and 'Agra Tech VC-1' cultivars and reduced

percentage of extra large and jumbo kernels in 'Florunner' and 'Sunrunner' cultivars

(Richburg el al. 1995). Research in Texas has shown at 14 DAT, diclosulam applied

PRE at 18 and 27 g ai/ha injured 'Flavor Runner 458', 'Sunoleic 97R', 'TX 977006', and

'Georgia Hi O/L' varieties 10-40% but did not injure the conventional variety 'Tamrun

96'. Injury continued 20 to 25% 42 DAT for the 'Flavor Runner 458' and 'Sunoleic 97R'

varieties and 35 to 45% for the 'Georgia Hi O/L' from diclosulam applied PRE at 27 g

ai/ha. In a 2000 test conducted in Florida where diclosulam was applied PPI at 0, 18, 27,

or 54 g ai/ha to three runner market-type peanut cultivars, 'Georgia Green', 'C-99R', and

'MDR 98', peanut injury was not observed and canopy diameter was unaffected at any

rate at any location in either year (Main et al. 2002). In 2000, diclosulam caused









stunting, stand loss, and chlorosis to peanut when applied PPI and PRE. Therefore, a

supplemental label was issued in 2001 for Texas and New Mexico changing

preemergence application timing to no less than five days after planting through at-

cracking at 26.8g ai/ha. The supplemental label for Oklahoma restricted diclosulam

application to immediately after planting through at-cracking at no more than 20. Ig ai/ha

(Strongarm 2001).

Flumioxazin was registered in 2001 and during its first year, injury was reported in

Oklahoma, Georgia, North Carolina, and West Texas (Murphree et al. 2003). Early-

season injury was a minor concern with flumioxazin when the herbicide was first

introduced however in 2002 Main et al. observed some injury due to cool wet conditions

in runner type varieties. Up to 25% flumioxazin injury was observed 14 and 28 DAT

with the cultivars 'Georgia Green, 'C-99R, and 'MDR-98'. Injury was still evident at 56

DAT but only with flumioxazin applied at 211 g/ha. In some cases, less than 5% injury

14 DAT was observed on all varieties from flumioxazin applied PRE at 105g ai/ha with

all varieties tested (Murphree et al. 2002). Therefore, it is important to determine

whether newer cultivars are tolerant to current herbicide application practices.

In 2002, seven new peanut cultivars ('AP-3', 'Carver', 'DP-1', 'GP-1', 'Hull',

'ANorden', 'UF00324') are in various stages of development and releases by Dr. D. W.

Gorbet at the University of Florida. None of these cultivars have been evaluated for

tolerance to herbicides. The objective of this study was to determine response of these

new cultivars to commonly used herbicides in peanut production.

Materials and Methods

Field studies were conducted in 2003 at the West Florida Research and Education

Center near Jay, FL and at the Plant Science Research and Education Center near Citra,









FL. Jay is located in the far West panhandle of Florida with soil type of Red Bay sand

loam (fine-loamy, siliceous, thermic, Rhodic paleudults) at pH 5.8 and organic matter of

2.1%. Citra is located in North Central Florida with soil type Sparr sand (loamy,

siliceous, hyperthermic, Grossa-renic paleudult) with organic matter 1% and pH of 6.4.

Conventional tillage system consisting of deep moldboard plowing, leveling disking and

one field cultivation prior to planting was used to prepare the field for peanut planting.

Pendamethalin was applied at 1.12kg ai/ha PPI to the entire test at all locations for

control of small-seeded broadleaf and annual grasses.

Peanuts were planted under conventional tillage at both locations. Seven recently

released runner-type varieties, ('AP-3', 'Carver', 'DP-1', 'GP-1', 'Hull', 'ANorden',

'UF00324'), along with a standard variety (C-99R) were planted on May 8, 2003 at Jay,

FL and May 15, 2003 at Citra, FL at a depth of 6 cm and seeding rate of 122 kg/ha.

Peanuts were planted in 91cm single rows at both locations. Plots at Citra consisted of

four rows, 3.0m wide and 6.1 m long. Plots at Jay consisted of four rows, 3.0m wide and

7.0m long. A split-plot design was utilized with four replications. The whole plot effect

was peanut varieties and the sub plot effect was five herbicide treatment combinations.

Soil fertilization and liming practices were in accordance with test

recommendations by the University of Florida Soil Testing Laboratory. Florida

Cooperative Extension Service recommendations were followed for management of

fungicide, insecticide, and irrigation.

Herbicide treatments and application rates listed in table 4.1 consist of five

herbicide systems commonly used by peanut growers. Rates of the herbicides were two

times that of the labeled rate in order to detect any differences in herbicide tolerance. All









at cracking (AC), early post (EPOST), POST, or 60 days after emergence (DAE)

treatments include a non-ionic surfactant (Induce) at 0.25 % V/V. Herbicides were

applied with a CO2 pressurized backpack sprayer calibrated to deliver 187 L/ha.

Plots were maintained weed-free throughout the growing season by cultivation and

hand hoeing. Crop injury was visually evaluated two weeks after PRE application, one

week after AC application, four weeks after EPOST application, and just prior to peanut

harvest. Peanut canopy diameter was measured 1, 2 and 4 wk after AC application and 3

wk after 60 DAE application. Visual evaluations of injury were recorded on a scale of 0

to 100% with 0 = no injury and 100 = crop death. Canopy diameter measurements (cm)

were recorded from 12 randomly selected plants from each plot and averaged.

The center two rows from each plot were harvested with conventional equipment at

physiological maturity for each variety as determined by the hull scrape method (Johnson

1987). Yields were adjusted to 8% moisture and converted to kilograms per hectare.

SAS (1996) Proc Mixed software was used to analyze the data. Data were

subjected to analysis of variance to test treatment effects and interactions. Means were

separated using Fisher's Protected LSD Test at the p
Results and Discussion

There was an interaction between treatment and location for canopy and yield

measurements, therefore, data will be presented by location. However, there was not a

location interaction for injury measurements so data will be pooled over locations.

Peanut Injury

There was an interaction between peanut cultivar and herbicide treatment;

therefore, data are presented for each cultivar and herbicide combination. Diclosulam

caused 10-21% visual injury 2 wk after PRE application with 'ANorden' and 'AP-3'









exhibiting the most significant damage (21%). Flumioxazin caused significant injury

(75-48%) on all varieties evaluated 2 wk after PRE application. 'UF00324' injury was

significantly the highest (75%) with 'DP-1', 'GP-1', and 'AP-3' displaying significantly

lower injury (56, 50, 48%, respectively).

When evaluated 1 wk after application of paraquat following diclosulam PRE, 'DP-

1' exhibited the most injury (51%) while 'UF00324' showed the least damage (32%).

All varieties recovered slowly by 7 wk after AC (15-23%), however, recovery was

slowest for 'C-99R' (23%). By 17 wk after AC recovery was complete for all varieties

(<10%). Paraquat AC applied without a PRE application stunted 'Carver' and 'C-99R'

the most (35 and 36%, respectively) and 'Hull' and 'GP-1' the least (26 and 25%,

respectively) one week after treatment (Table 4.2). Seven weeks after AC application

stunting was less for all varieties. At that time 'AP-3' and 'Hull' recovered the slowest

and exhibiting the most injury (26 and 25%) and 'GP-1' the least (11%). When evaluated

7 wk after application of paraquat AC following flumioxazin, injury was between 31 and

13% with 'ANorden' and 'DP-1' displaying the most injury and 'GP-1' the least (31 and

13%, respectively).

When evaluated 4 wk after imazapic EPOST application injury remained (37-26%)

with 'AP-3' the most and 'DP-1' the least (37% and 26%, respectively). By 10 wk after

EP, injury was less than 15% for all varieties. Peanut recovered (<15%) by the time of

the last evaluation.

When evaluated 5 wk after chlorimuron 60 DAE application, injury ranged from 5-

21% stunting. 'Hull' was significantly the least tolerant variety and 'ANorden'

significantly tolerated the most (21% and 5% injury, respectively).









Canopy

At Jay, there was not a significant main effect of variety or a variety by treatment

interaction. Canopy means were averaged across all varieties for each treatment at each

time of measurement and compared to treatment #5 the non-treated control (Table 4.3).

All treatment canopy measurements were significantly different from the non-treated

control at each time of measurement except for treatments using diclosulam PRE or

flumioxazin PRE fb paraquat AC when measured at three weeks after the 60DAE

application. This may be due to not receiving a treatment after the AC application.

Diclosulam PRE fb paraquat provided the least reduction in canopy when compared to

the control (79.6 and 79.8cm, respectively) late season and at each time of measurement.

Paraquat AC fb chlorimuron 60 DAE caused the most reduction in canopy when

compared to the control late season (73.0 and 79.8cm, respectively).

At Citra, there was a significant main effect of variety (Table 4.4) and of herbicide

treatment (Table 4.3). Canopy measurements for each variety were averaged over all

treatments. 'DP-1' and 'Hull' consistently had the lowest canopy at each time of

measurement (Table 4.8). 'GP-1' and 'ANorden' showed the highest level of tolerance

to the herbicides the best resulting in significantly higher canopy diameter for most

measurement timings at 3 wk after 60 DAE. 'UF00324' produced the largest canopy

resulting in the highest canopy measurement followed by 'ANorden' and 'GP-1' (89,

88.6 and 84.6cm, respectively).

When canopy means were averaged over varieties for each treatment, results

indicated significant differences when compared to the non-treated control (Table 4.3).

Canopy size was significantly reduced for all treatments at all measurement times when

compared to the non-treated control. Paraquat AC fb imazapic POST caused the most









reduction in canopy size when compared to the control (78.1 and 88.1 cm, respectively)

late season and at each time of measurement. Paraquat AC fb chlorimuron 60DAE

resulted in the next highest canopy damage but only at the last measurement 3 wk after

chlorimuron was applied. Later measurements indicate canopy recovery for the POST

and 60DAE application treatments. Flumioxazin PRE fb paraquat AC resulted with less

canopy damage at 1 wk after PRE and at last measurement when compared to diclosulam

PRE fb paraquat AC (59.9, 55.5cm and 86.2, 83.8 cm, respectively).

Peanut Yield

At Jay, there was a significant main effect of variety (Table 4.5) and of herbicide

treatment (Table 4.6); however, there was not a variety by treatment interaction. Variety

AP-3 was the lowest yielding (1894 kg/ha) and significantly lower than 'Carver' and

'DP-1' (3195 and 3531 kg/ha, respectively), the highest yielding when averaged across

all treatments.

Yields of treatments using paraquat AC fb chlorimuron 60DAE, imazapic POST, or

flumioxazin PRE at Jay, when averaged over all varieties, was significantly lower than

the non-treated control which yielded highest. Flumioxazin PRE fb paraquat AC resulted

in the lowest yield (2820 kg/ha) and next lowest was paraquat AC fb imazapic POST

(2840 kg/ha). These yield reductions were most likely the result of the 2x rates used in

this study to insure detection of any differences that exist among peanut cultivars.

At Citra, there was an interaction between variety and treatment. Significant

differences among many varieties were observed when each variety was compared to

their non-treated control (Table 4.7). DP-1 was the only variety where yield for all four

treatments was significantly lower than the non-treated (5810 kg/ha). Carver, GP-1,

'ANorden', and 'UF00324' were the varieties where yield for all four treatments were not









significantly different from their non-treated check (5150, 4540, 4613, and 5199 kg/ha,

respectively). This suggests that the four treatments had little to no effect on the yield of

these four varieties when compared to the non-treated control.

Treatment with paraquat AC fb imazapic POST consistently resulted in

significantly lower yields compared to the non-treated control for the remaining varieties,

'AP-3', 'C-99R', and 'Hull' (5712, 4467, 4078 kg/ha, respectively). Yield of 'C-99R'

was also reduced by the treatment using paraquat AC fb chlorimuron 60 DAE (4223

kg/ha).

Canopy size and yield were significantly affected by the 2x rates of herbicides used

in this study. At Citra, AP-3 exhibited some foliar damage, however, it provided the

highest yield. DP-1 and Hull varieties displayed the most damage to canopy and were

also the lowest yielding. When each variety's treatments were compared to the non-

treated, DP-1 resulted in the greatest yield reduction. Paraquat AC fb imazapic POST

resulted in significant yield reduction for 'AP-3', 'C-99R', 'DP-1', and 'Hull'.

At Jay, canopy damage was minimal and significant only up to 2 wk after EP for

'Carver' and 'DP-1'. 'AP-3', 'GP-1' and 'C-99R' resulted in the lowest yield when

averaged over all treatments possibly a result from the lowest yielding treatments of

flumioxazin PRE fb paraquat AC and paraquat AC fb imazapic POST. Flumioxazin PRE

fb paraquat AC resulted in the highest canopy reduction however recovered late season to

become non-significant. 'Carver' and 'UF00324' consistently had high yield at both

locations with minimal canopy reduction.

The results from these studies indicate that peanut varieties respond differently to

commonly used herbicides. Therefore, it is important to determine whether newer









cultivars are tolerant to current herbicide application practices. Among all treatments,

'GP-1' and 'Hull' displayed the least visual injury when evaluated 1 to 4 wk after

application. All varieties recovered late-season with <15% injury. However, when

canopy measurements and yield was evaluated, results differed. Three varieties

displayed the least canopy reduction and were the higher yielding. 'Carver', 'GP-1', and

'ANorden' were not significantly affected by herbicide treatments when compared to

their non-treated control. Yields ranged from 5614 to 2820 kg/ha with 'Carver' yielding

the highest. 'GP-1' is an early maturing variety with some TSWV resistance. 'ANorden'

and 'Carver' are both medium maturity varieties with good tomato spotted wilt virus

(TSWV) and disease resistance with higher yield than 'Georgia Green'. 'ANorden

yielded lower than 'Carver'; however, it has better TSWV and disease resistance. Using

'ANorden may result in less usage of pesticides; however, the higher yield of 'Carver'

may make up for the increased use. Economic returns need to be analyzed to determine

which variety results in higher total revenue.









Table 4.1-Variety tolerance herbicide treatments, Jay and Citra, FL. 2003

Abbreviation Treatment Rate Timing
g ai/ha
Par+chl Paraquat 140 AC fb
Chlorimuron 9 60 DAE

Ds+par Diclosulam 53.6 PRE fb
Paraquat 140 AC

Par+im Paraquat 140 AC fb
Imazapic 70.6 EPOST

Fl+par Flumioxazin 210.6 PRE fb
Paraquat 140 AC

Check Non-treated
AC, EPOST, and 60DAE treatments received a surfactant at 0.25% V/V









Table 4.2-Percent injury as affected by treatments compared to non treated check for
each variety at each measurement interval pooled over locations.
Treatment I Varieptxj ? vuVPRF 1 wkx1 A Cw AA-FP v---0ThAF


C-99R
DP- 1
GP-1
Hull
ANorden
Carver
AP-3
UF00324
LSD

C-99R
DP-1
GP-1
Hull
ANorden
Carver
AP-3
UF00324
S1nM


---------------------------% inju -------------------------------
0 34 19 9
0 30 18 14
0 25 11 7
0 26 25 21
0 30 17 5
0 35 15 9
0 34 26 13
0 27 16 9
NS NS NS 6.6


Par+im C-99R 0 36 30 8
DP-1 0 28 26 10
GP-1 0 33 26 12
Hull 0 27 33 15
ANorden 0 36 31 7
Carver 0 31 31 11
AP-3 0 25 37 6
UF00324 0 23 30 9
LSD NS 6.7 NS NS

Fl+par C-99R 63 33 30 8
DP-1 56 32 31 10
GP-1 50 28 13 4
Hull 67 28 27 13
ANorden 71 33 31 15
Carver 68 30 28 12
AP-3 48 32 23 10
UF00324 75 30 23 7

LSDa 9.3 NS 10.5 NS


a Fisher's Protected LSD procedure A P<0.1


Par+chl


Ds+par










Table 4.3-Canopy means for each treatment averaged over all varieties at Jay and Citra,
FL.

Treatment 1 Week EP 2 Weeks EP 4 Weeks EP 3 Weeks 60 DAE

Jay, FL (cm)
Par+chl 45.8* 62.3* 71.1* 73.0*
Ds+par 47.7* 64.8* 71.6* 79.6
Par+im 38.3* 56.3* 67.9* 74.1*
Fl+par 32.4* 50.8* 67.5* 76.8
Check 52.9 69.4 76.0 79.8
Citra, FL

Par+chl 60.7* 71.0* 76.7* 80.4*
Ds+par 55.5* 65.6* 77.5* 83.8*
Par+im 50.2* 59.8* 71.1* 78.1*
Fl+par 59.9* 70.1* 78.3* 86.2*
Check 65.2 75.2 81.4 88.1

* significance as compared to non-treated #5 at p< 0.1 level






85


Table 4.4-Canopy means for each variety averaged over treatments at Citra, Fl.


Treatment'


1 Week EP 2 Weeks EP 4 Weeks EP 3 Weeks 60 DAE
Citra, FL (cm)


AP-3 58.9 69.2 72.8 78.7
C-99R 54.2 64.8 74.8 84
Carver 64.7* 75.2* 80.7 85.7
DP-1 47.5* 57.4* 68.7 75.9*
GP-1 65.5* 74.5* 81.1 84.6
Hull 51.5 61.6 74 79.9
ANorden 65* 75* 83* 88.6
UF00324 59.5 69 80.9 89
*Canopy significantly different from conventional variety (C-99R) at p< 0.1 level






86


Table 4.5 Yield of each variety averaged over all treatments at Jay, FL
Variety Yield p value vs AP-3
kg/ha
AP-3 1894 ----
C-99R 3116 0.076
Carver 3195 0.046*
DP-1 3531 0.005*
GP-1 2820 0.5005
Hull 3130 0.0705
ANorden 3101 0.0850
UF00324 3152 0.0610
* Significantly different form AP-3 variety a p< 0.1 level







87


Table 4.6 -Yield as affected by treatments averaged over all varieties at Jay, FL.

Treatment Yield p values trt #5
kg/ha
Par+chl 2882 0.0327*
Ds+par 3138 0.7388
Par+im 2840 0.0155*
Fl+par 2820 0.0104*
Check 3283 ---------

* Yield significantly different form treatment #5 (control) at p< 0.1 level









Table 4.7 -Yield of each variety per treatment with significance compared to the non-
treated control (check)
Citra, FL

Variety Treatment Yield VarietyTreatment Yield
kg/ha kg/ha

AP-3 Par+chl 6347 GP-1 Par+chl 4028
AP-3 Ds+par 6884 GP-1 Ds+par 4296
AP-3 Par+im 5712* GP-1 Par+im 4247
AP-3 Fl+par 6103 GP-1 Fl+par 4980
AP-3 Check 6933 GP-1 Check 4540
C-99R Par+chl 4223* Hull Par+chl 4638
C-99R Ds+par 5053 Hull Ds+par 4906
C-99R Par+im 4467* Hull Par+im 4078*
C-99R Fl+par 5224 Hull Fl+par 5114
C-99R Check 5663 Hull Check 5199
Carver Par+chl 5614 ANorden Par+chl 4833
Carver Ds+par 5248 ANorden Ds+par 5150
Carver Par+im 5224 ANorden Par+im 4613
Carver Fl+par 5248 ANorden Fl+par 5150
Carver Check 5150 ANorden Check 4613
DP-1 Par+chl 4003* UF00324 Par+chl 4882
DP-1 Ds+par 4052* UF00324 Ds+par 4955
DP-1 Par+im 4174* UF00324 Par+im 4711
DP-1 Fl+par 4418* UF00324 Fl+par 5150
DP-1 Check 5810 ITF00324 Check 5199
*Yield significantly different from non-treated control at p< 0.1 level














CHAPTER 5
SUMMARY AND CONCLUSIONS

These studies indicate reduced rates of diclosulam and flumioxazin, followed by

imazapic can be used in Florida peanut production, provide adequate weed control

without compromising yield and provide total revenue equal to or higher than the

regional standard. Commonly used herbicides organized in combinations that are more

cost efficient can control weeds without affecting yield and can also reduce the 40% of

total production cost utilized for pesticides. With the release of seven new peanut

varieties from the University of Florida, testing tolerance to commonly used herbicides is

crucial to perform before applying reduced herbicide practices. The following summaries

of these experiments could provide a foundation for peanut weed management on

conventional and new peanut varieties utilizing reduce herbicide inputs therefore

reducing cost and increasing total revenue.

In 2002, weed management greater than 90% was achieved with diclosulam mixed

with flumioxazin at 1/4X followed by imazapic at 2/3x at both Jay and Citra locations for

common cocklebur, sicklepod, yellow nutsedge, pigweed, hairy indigo, and Florida

beggarweed.

In 2003, weed control at Jay was greater than 87% with all treatments for wild

poinsettia and smallflower morningglory. Sicklepod control reached 85% only with full

rates of diclosulam or flumioxazin fb imazapic or the regional standard. Florida

beggarweed was not controlled >80% with diclosulam alone or when it was followed by

imazapic at 1/4x or by imazapic alone. Flumioxazin at all rates provided the best Florida









beggarweed control; however, purple nutsedge control greater than 80% required a

sequential treatment of imazapic. Diclosulam at 1/2x alone and followed by imazapic at

1/4x provided greater than 85% control of purple nutsedge.

Weed control at Citra was representative of an area with low weed pressure. The

weed species with the highest density was tropical spiderwort and it may have reduced

populations of other species. Greater than 80% control was observed with all treatments

for purple nutsedge, sicklepod, hairy indigo, and cutleaf groundcherry. Florida

beggarweed, similar to Jay, was not controlled with diclosulam alone or when it was

followed by imazapic at 1/4x.

Tropical spiderwort control was controlled by more treatments in twin row planting

and required only diclosulam plus flumioxazin followed by imazapic at 1/4x to achieve

82% control. In single row planting, 1/2x rate of these three herbicides was required to

obtain 86% control. All treatments resulted in peanut yield higher than the untreated

check but there were no differences among the reduced rate treatments. When total

revenue was calculated based on yield and cost per treatment, diclosulam plus

flumioxazin followed by imazapic at 1/2x provided the highest total revenue earned for

both locations.

Reduced cost herbicide systems demonstrate they can provide weed control and

higher total revenue when compared to the regional standard. Results in 2002 and 2003

at all locations had a similar trend. Pendimethalin was necessary to obtain grass control

greater than 70% unless grass pressure was low then metolachlor provided adequate

control. Metolachlor plus paraquat followed by 2,4-DB provided greater than 84%

control of all weeds at Jay and cost only $38 per hectare, $20 less than the regional









standard. Even though it provided good weed control, it was not one of the higher total

revenue treatments. Treatments using pendimethalin followed by imazapic at 3/4x,

pedimethalin followed by imazapic at 1/2x plus 2,4-DB, and pendimethalin followed by

diclosulam PRE and paraquat AC followed by 2,4-DB provided greater than 80% weed

control.

At the Marianna site, pendimethalin PPI alone or fb diclosulam PRE then fb

imazapic at 1/2x and/or mixed with 2,4-DB POST were the highest yielding herbicide

program. Treatment costs were $9, $14, and $12/ha less and returned $60, $262, and

$149/ha more than the regional standard.

Studies conducted to evaluate herbicide tolerance in selected peanut cultivars

indicate that certain peanut varieties are more tolerant than others and are affected

differently depending on the herbicide systems. Yield and canopy were significantly

affected by the higher than labeled rates of herbicides used in this study to insure

detection of varietal differences.

'DP-1' and 'Hull' displayed the greatest injury late season from paraquat AC fb

chlorimuron at 2x. All varieties displayed 23-36% injury from paraquat AC alone. All

varieties exhibited < 21% injury from diclosulam PRE with 'AP-3 and 'Norden'

displaying the most (21%). When paraquat was applied AC following diclosulam, injury

increased for all varieties, some more than others. 'DP-1' was the most effected by

paraquat with injury increasing from 15% to 51%. 'AP-3' displayed the least effect from

paraquat only increasing injury form 21 to 33%. Flumioxazin PRE injured 'UF00324'

and 'Norden' (75, 71%) and imazapic injury was highest for 'AP-3' and 'Hull' (37,

33%). All varieties recovered late season with injury < 15%. Variety canopy cover was