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Management of Herbicide Resistant Palmer Amaranth (amaranthus Palmeri) in Peanut

Permanent Link: http://ufdc.ufl.edu/UFE0041375/00001

Material Information

Title: Management of Herbicide Resistant Palmer Amaranth (amaranthus Palmeri) in Peanut
Physical Description: 1 online resource (61 p.)
Language: english
Creator: Dobrow, Michael
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Palmer amaranth (PA) (Amaranthus palmeri), a C4 summer annual, is a pigweed species native to Mexico and the southwestern United States. This pigweed species can grow up to 2 meters in height and is a prolific seed producer. PA began to increase in scope and severity throughout the peanut producing regions of the southeastern United States during the last 25 years. In addition to PA?s competitiveness, this species has developed resistance to four different classes of herbicides throughout the United States. Imazapic, an inhibitor of acetolactate synthase (ALS), is an important herbicide for the control of PA in peanut. However, extensive use in peanut production in the southeast, PA has been selected for ALS-resistance. Peanut growers need management strategies to help control herbicide resistant PA, this research was designed to develop strategies to control PA. Project I evaluated the effect of three rye cover crop management scenarios that included peanut planting into standing rye cover, rolled cover, or no cover. Within each cover crop scenario several soil active herbicides were applied. Plant counts were taken weekly until a threshold of 1 PA per meter of row was achieved. Premergence (PRE) applied pendimethalin or norflurazon, and the untreated controls reached the threshold within 9 days of application for all cover crop scenarios. Metolachlor applied PRE delayed time to thresholds by 23 days in year one and ? 1 day in year two. Flumioxazin applied PRE and metolachlor applied at-cracking (AC) were the most effective herbicide treatments. Both herbicides delayed PA reaching threshold levels by > 54.62 days in 2008 and > 12.59 days in 2009. Project II evaluated the effects of fomesafen alone, at varied rates, or combined with other herbicides, applied PRE, AC, and postemergence (POST), on peanut injury and PA control over two years. Peanut injury was observed for most treatments but was transient and peanuts fully recovered within 28 days after application. Peanut yield was not reduced significantly for any fomesafen treatment in either year. Control of PA was ? 78% when fomesafen alone was applied AC at ? 0.42 kg/ha. Combined applications of paraquat + bentazon + 2, 4-DB with fomesafen controlled PA ? 85% for all rates used. Project III evaluated the effect of lactofen applied with two spray nozzle types, carrier volumes, and PA height ranges of 5 to 10 cm and 15 to 20 cm. Control of PA, at the shorter heights was not affected by spray nozzle type or carrier volume. However, lactofen applied to taller PA was less effective when applied at 94 L/ha, compared to carrier volumes of 187 and 281 L/ha. In conclusion, PA control could be achieved with the use of flumioxazin applied PRE and metolachlor applied AC. Cover crop had very little affect on control of PA. The use of fomesafen at ? 0.42 kg/ha is needed to control PA effectively when applied alone AC. But, when combined with paraquat + bentazon + 2, 4-DB a higher fomesafen rate is not needed. A carrier volume of ? 187 L/ha is needed to control PA at ? 15 cm when lactofen is applied. Peanut producers need an application of flumioxazin or fomesafen PRE combined with a POST application of a contact herbicide + metolachlor to control ALS-resistant PA.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Michael Dobrow.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Ferrell, Jason A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041375:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041375/00001

Material Information

Title: Management of Herbicide Resistant Palmer Amaranth (amaranthus Palmeri) in Peanut
Physical Description: 1 online resource (61 p.)
Language: english
Creator: Dobrow, Michael
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Palmer amaranth (PA) (Amaranthus palmeri), a C4 summer annual, is a pigweed species native to Mexico and the southwestern United States. This pigweed species can grow up to 2 meters in height and is a prolific seed producer. PA began to increase in scope and severity throughout the peanut producing regions of the southeastern United States during the last 25 years. In addition to PA?s competitiveness, this species has developed resistance to four different classes of herbicides throughout the United States. Imazapic, an inhibitor of acetolactate synthase (ALS), is an important herbicide for the control of PA in peanut. However, extensive use in peanut production in the southeast, PA has been selected for ALS-resistance. Peanut growers need management strategies to help control herbicide resistant PA, this research was designed to develop strategies to control PA. Project I evaluated the effect of three rye cover crop management scenarios that included peanut planting into standing rye cover, rolled cover, or no cover. Within each cover crop scenario several soil active herbicides were applied. Plant counts were taken weekly until a threshold of 1 PA per meter of row was achieved. Premergence (PRE) applied pendimethalin or norflurazon, and the untreated controls reached the threshold within 9 days of application for all cover crop scenarios. Metolachlor applied PRE delayed time to thresholds by 23 days in year one and ? 1 day in year two. Flumioxazin applied PRE and metolachlor applied at-cracking (AC) were the most effective herbicide treatments. Both herbicides delayed PA reaching threshold levels by > 54.62 days in 2008 and > 12.59 days in 2009. Project II evaluated the effects of fomesafen alone, at varied rates, or combined with other herbicides, applied PRE, AC, and postemergence (POST), on peanut injury and PA control over two years. Peanut injury was observed for most treatments but was transient and peanuts fully recovered within 28 days after application. Peanut yield was not reduced significantly for any fomesafen treatment in either year. Control of PA was ? 78% when fomesafen alone was applied AC at ? 0.42 kg/ha. Combined applications of paraquat + bentazon + 2, 4-DB with fomesafen controlled PA ? 85% for all rates used. Project III evaluated the effect of lactofen applied with two spray nozzle types, carrier volumes, and PA height ranges of 5 to 10 cm and 15 to 20 cm. Control of PA, at the shorter heights was not affected by spray nozzle type or carrier volume. However, lactofen applied to taller PA was less effective when applied at 94 L/ha, compared to carrier volumes of 187 and 281 L/ha. In conclusion, PA control could be achieved with the use of flumioxazin applied PRE and metolachlor applied AC. Cover crop had very little affect on control of PA. The use of fomesafen at ? 0.42 kg/ha is needed to control PA effectively when applied alone AC. But, when combined with paraquat + bentazon + 2, 4-DB a higher fomesafen rate is not needed. A carrier volume of ? 187 L/ha is needed to control PA at ? 15 cm when lactofen is applied. Peanut producers need an application of flumioxazin or fomesafen PRE combined with a POST application of a contact herbicide + metolachlor to control ALS-resistant PA.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Michael Dobrow.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Ferrell, Jason A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041375:00001


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1 MAN AGEMENT OF HERBICIDE RESISTANT PALMER AMARANTH (Amaranthus palmeri ) IN PEANUT By MICHAEL HUGH DOBROW JR. 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 2010

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2 2010 Michael Hugh Dobrow Jr.

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3 To my wife loving wife, Casey, as well as my parent s Mike and Mitchell whose l ove and support has never ended

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4 ACKNOWLEDGMENTS For their support and guidance through my graduate studies, I wish to express sincere appreciation to my graduate committee: Dr. Jay Ferrell, Dr. Greg MacDonald, Dr. Barry Brecke, Dr. John Erickson and Dr. Wils on Faircloth. Special thanks to committee chair Dr. Jay Ferrell, for providing me the opportunity and guidance to further my education in weed science. Without his assistance, I would have never achieved this degree. I thank all who helped me with my research, including Jim Boyer, Barton Wilder, Bra n don Fast, Sergio Morichetti, Kurt Vollmer, Courtney Stoke s, Jing Jing Wang, Sarah Berger and all the staff at the Plant Science Research and Education Unit. Special thanks go to Jim Boyer, for his morale boosting pep talks and assistanc e in the field that brought me much needed encouragement and support Also, I thank the Hand Foundation for their funding that provided the additional support needed to reach my goals. My mother and father have been supportive, along with my sister Shannon, and grandparents; Oscar, Murray, and Vera. T hank you for providing encouragement and love that only family can offer I thank my wife for her love, support and sacrifice. Without her in my life, I would not be the man I am today.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...................................................................................................... 4 LIST OF TABLES ................................................................................................................ 6 LIST OF FIGURES .............................................................................................................. 8 ABSTRACT .......................................................................................................................... 9 CHAPTER 1 THE EFFECT OF COVER CROP AND PREMERGENCE HERBICIDES ON THE CONTROL OF ALS -RESISTANT PALMER AMARANTH IN PEANUT ........... 12 Introduction ................................................................................................................. 12 Materials and Methods ............................................................................................... 15 Results and Discussion .............................................................................................. 17 2 EVALUATION OF FOMESAFEN HERBICIDE FOR ALS -RESISTANT PALMER AMARANTH CONTROL AND EFFECT ON PEANUT INJURY/YIELD .................... 23 Introduction ................................................................................................................. 23 Materials and Methods ............................................................................................... 25 Results and Discussion .............................................................................................. 28 Fomesafen Alone ................................................................................................. 28 Fomesafen Management ..................................................................................... 31 3 THE INFLUE NCE OF CARRIER VOLUME, NOZZLE TYPE, AND PLANT HEIGHT ON CONTROL OF PALMER AMARANTH IN PEANUT ............................ 44 Introduction ................................................................................................................. 44 Materials and Methods ............................................................................................... 46 Spray Coverage Study ......................................................................................... 46 Field Study ........................................................................................................... 46 Results and Discussion .............................................................................................. 48 Quantifying Spray Coverage ............................................................................... 48 Field Study ........................................................................................................... 48 LIST OF REFERENCES ................................................................................................... 54 BIOGRAPHICAL SKETCH ................................................................................................ 61

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6 LIST OF TABLES Table page 1 -1 Influence of preemergence and post herbicides on Palmer amaranth days to threshold in 2008. ................................................................................................... 20 1 -2 Influence of cover crop scenarios none, rolled and standing combined with preemergence and post herbicides on Palmer amaranth days to threshold in 2009. ....................................................................................................................... 21 1 -3 Monthly average of rainfall (mm) for May through August at Sandlin farm in 2008 and 2009. ...................................................................................................... 22 2 -1 Influence of fomesafen and flumioxazin on % injury, days to row closure, and yield of peanut in 2008 at Citra, FL (weed -free). ................................................... 34 2 -2 Influence of fomesafen and flumioxazin at varied rates on % injury, days to row closure, and yield of peanut in 2009 at Citra, FL (weed-free). ...................... 35 2 -3 Influence of fomesafen and flumioxazin on % control of Palmer amaranth in 2008 at Williston, FL (weedy). ............................................................................... 36 2 -4 Influence of fomesafen and flumioxazin on % control of Palmer amaranth in 2009 at Williston, FL (weedy). ............................................................................... 37 2 -5 Influence of fomesafen on % injury of Palmer amaranth in 2008 at Williston, FL (weedy). ............................................................................................................. 38 2 -6 Influence of fomesafen and flumioxazin combined with other postemergence herbicides on % injury of peanut in 2008 at Citra, FL (weed -free). ...................... 39 2 -7 Influence of fomesafen and flumioxazin combined with other postemergence herbicides on % injury of peanut in 2009 at Citra, FL (weed -free). ...................... 40 2 -8 Influence of fomesafen and flumioxazin on days to row closure and yield of peanut in 2008 and 2009 at Citra, FL (weed -free). ............................................... 41 2 -9 Influence of fomesafen and flumioxazin combined with other post emergence herbicides on % control of Palmer amaranth in 2008 at Williston, FL (weedy). .. 42 2 -10 Influence of fomesafen and flumioxazin combined with other post emergence herbicides on % control of Palmer amaranth in 2009 at Williston, FL (weedy). .. 43 3 -1 Influence of carrier volume on % control of Palmer amaranth (height range of 5 cm to 10 cm) with the use of lactofen (0.21 kg/ha) + crop oil concentrate 1% (v/v). .................................................................................................................. 52

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7 3 -2 Influence of carrier volume on % control of Palmer amaranth (h eight range of 15 cm to 20 cm) with the use of lactofen (0.21 kg/ha) + crop oil concentrate (1% v/v). .................................................................................................................. 53

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8 LIST OF FIGURES Figure page 3 -1 Influence of varying carrier volumes and nozzle type on percent spray coverage. ................................................................................................................ 51

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9 Ab stract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requi rements for the Degree of Master of Science MANAGEMENT OF HERBICIDE RESISTANT PALMER AMARANTH (AMARANTHUS PALMERI) IN PEANUT By Michael Hugh Dobrow Jr. May 2010 Chair: Jason Ferrell Major: Agronomy Palmer amaranth (PA) ( Amaranthus palmeri ), a C4 summer annual, is a pigweed species native to Mexico and the southwestern United States. This pigweed species can grow up to 2 meters in height and is a prolific seed producer. PA began to increase in scope and severity throughout the peanut producing regions of the southeastern United States during the last 25 years. In addition to PA s competitiveness, this species has developed r esistance to four different classes of herbicides throughout the United States. Imazapic, an inhibitor of aceto lactate synthase (ALS), is an important herbicide for the control of PA in peanut. However, extensive use in peanut production in the southeast PA has been selected for ALS -re sistance. Peanut growers need management strategies to help control herbicide resistant PA, this research was designed to develop strategies to control PA. Project I evaluated the effect of three rye cover crop management scenarios that included peanut planting into standing rye cover rolled cover, or no cover Within each cover crop scenario several soil active herbicides were appli ed. Plant counts were taken weekly until a threshold of 1 PA per meter of row was achieved. Premergence (PRE) applied pendimethalin or norflurazon, and the untreated controls reached the

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10 threshold within 9 days of application for all cover crop scenarios. Metolachlor applied PRE delayed time to thresholds by 23 days in year one and 1 day in year two. Flumioxazin applied PRE and metolachlor applied at -cracking (AC) were the most effective herbicide treatments. Both herbicides delayed PA reaching threshold levels by > 54.62 days in 2008 and > 12.59 days in 2009. Project II evaluate d the effects of fomesafen alone, at varied rates, or combined with other herbi cides, applied PRE, AC, and postemergence (POST) on peanut injury and PA control over two years Peanut injury was observed for most treatments but was transient and peanuts f ully recovered within 28 days after application. Peanut yield was not reduced significantly for any fomesafen treatment in either year Control of PA was was applied AC at Combined applications of paraquat + bent azon + 2, 4 DB with fomesafen controlled PA effect of lactofen applied with two spray nozzle types, carrier volumes, and PA height ranges of 5 to 10 cm and 15 to 20 cm. Control of PA, at the shorter hei ghts was not affected by spray nozzle type or carrier volume. However lactofen applied to taller PA was less effective when applied at 94 L/ha, compared to carrier volumes of 187 and 281 L/ha. In conclusion, PA control could be achieved with the use of flumioxazin applied PRE and m etolachlor applied AC. C over crop had very little affect on control of PA. The use of fomesafen at alone AC. But, when combined with paraquat + bentazon + 2, 4-DB a higher fomesafen rate is not needed. A carrier volume of when lactofen is applied. Peanut producers need an application of flumioxazin or

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11 fomesafen PRE combined with a POST application of a contact herbicide + metolachl or to control ALS resistant PA.

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12 CHAPTER 1 THE EFFECT OF COVER CROP AND PREMERGENCE HERBICIDES ON THE CONTROL OF ALS -R ESISTANT PALMER AMAR ANTH IN PEANUT Int r oduction Palmer amaranth (PA) ( Amaranthus palmeri S. Wats) is a native species of Mexico and the southwestern United States (Steckel 2007). PA is a C4 summer annual (Ehlering er 1983) that is common in the peanut producing regions of the southeastern United States (Gleason and Cronquist 1991; Horak Lough in 2000). It is one of three dioecious Amaranthus spp. that has become an important weed in agronomic cropping systems in North America (Steckel 200 7). Previous research found that PA produced more leaf area, dry weight, and plant volume as compared to common waterhemp (Amaranthus rudis S.), another dioecious Amaranthus species (Horak and Loughin 2000). Competitiveness of PA can be attributed to its tremendous seed production, 250,700 to 613,074 seeds per female plant (Sellers et al. 2003; Keely et al. 1987), and aggressive growth habits, reaching heights of 2 meters (Bryson and DeFelice 2009). Due to these attributes, PA is considered a troublesome weed in Flori da, Georgia, and Sou th Carolina (Webster 2005). The competitive growth causes PA to greatly interfere with crop growth and yield potential. In Kansas, PA populations of 0.5 to 8 plants m1 of row reduced corn ( Zea mays L.) yields 11 to 91% (Massinga et al 2001; Massinga and Currie 2002). Klingman and Oliver (1994) reported soybean [ Glycine max (L.) Merr.] yield was reduced 17 to 68% with 0.33 to 10 PA plants per m1 of row, respectively. In Texas, PA populations from 1 to 10 plants per 9.1 m of row decr eased cotton ( Gossypium hirsutum L.) yiel ds from 13 to 54% (Morgan 2001). In addition, Smith et al. (2000) found that PA increased

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13 stripper cotton harvest time by 2to3-fold while Burke et al. (2007) reported that one PA plant per meter of row will reduce peanut yield by 28%. Imazapic (Cadre) and diclosulam (Strongarm), both acetolactate synthase (ALS) inhibiting herbicides, were registered in 1996 and 2000, respectively, for use in peanut. ALS -inhibiting herbicides control susceptible plant species by in hibiting the synthesis of branched chain amino acids (Shaner 1991; Saari et al. 1994). These herbicides have been widely adopted in many crops because of their low use rates, favorable toxicity profile wide crop selection, high efficacy, and cost effecti veness (Saari et al. 1994). ALS -inhibiting herbicides have been used in all major crops, but, t he intensive use of these herbicides has increased the incident of ALS -resistance. O ver 103 species have been documented with ALS -resistance, including PA (Heap 2009) PA, when not resistant, can be controlled effectively with imazapic (Grichar 1997; Grichar 2007). PA r esistance to ALS inhibiting herbicides has been confirmed in Arkansas, Florida, Georgia, Kansas, Mississippi, North Carolina, South Caroli na and Tennessee (Heap 2009). The use of cover crops has been incorporated into agronomic cropping systems for many years A cover crop system commonly consists of planting a winter -hardy crop in the fall, followed by desiccation and crop p lanting in the late spring (Moore et al. 1994). Residues from cover crops have been found to modify the soil microenvironment by altering the surface structure, intercepting light and precipitation (Liebman and Janke 1990), and affecting the transfer of heat and water b etween the soil and atmosphere (Facelli and Pickett 1991; Shaw and Rainero 1990; Stoller and Wax 1973). These modifications can help reduce soil erosion and runoff, while

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14 improving soil moisture retention, water infiltration, soil tilth, organic carbon and nitrogen (Mallory et al. 1998; Sainju and Singh 1997; Teasdale 1996; Varco et al. 1999; Yenish et al. 1996). Cover crops have been found to suppress weeds in row crops such as corn (Hoffman et al. 1993; Johnson et al. 1993), soybean ( Reddy 2001, Reddy 20 03, Liebl et al. 1992) and cotton (Hurst 1992). The patterns of weed emergence can be altered by cover crop residues, because of a moderating microclimate of the weed germination zone (Van Wijk et. al 1959; Willis et al. 1957). Also, residues create a ph ysical barrier that can restrict emergence of certain weeds (Facelli and Pickett 1991). Weed suppression may also occur from allelopathic compounds that release from cover crop residues (Barnes and Putnam 1986; Barnes et al. 1986; Shilling et al. 1986; Shilling et al. 1985). Burgo s et al. (1996) reported that the cover crops Italian rygrass ( Lolium perenne L.), oat ( Avena sativa ), and sorghum -sudangrass controlled PA 59, 32 and 42%, respectively, 9 weeks after crop planting. Other s tudies have indicated t hat additional weed management is needed when cover crops are used (Masiunas et al. 1995; Mohler and Teasdale 1993; Moore et al. 1994; Shilling et al. 1995; Teasedale and Mohler 1993). Premergence (PRE) herbicides are critical for a successful weed management program for ALS-resistant weeds in peanut however, there are a limited number of PRE herbicides registered in peanut. Currently, PRE herbicides registered in peanut that are non ALS -inhibitors include: flumioxazin (PPO -inhibitor), pendimethalin and e thalfluralin (microtubule inhibitors), norflurazon (pigment inhibitor) and metolachlor (l ong-chain fatty acid inhibitor). These herbicides vary i n their effectiveness on PA and a postemergence application of

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15 lactofen or acifluorfen is often necessary. Ho wever, lactofen and acifluor fen are labeled to control PA up to the 6 leaf stage or 10 cm in height (Anonymous 2007, Anonymous 2006). Considering that PA can grow up to 3.5 cm per day (Garvey 1999), there is very little time between when a preemergence herbicide begins to fail and the postemergence herbicide must be applied. Therefore, it is essential to better understand the relative length of control that each preemergence herbicide provides and how differing cover crop regimes impact the duration of co ntrol. Materials and Methods Field studies were conducted in 2008 and 2009 at Sandlin F arms near Williston, Florida on a Candler fine sand (hyperthermic, uncoated Typic Qu artzipsamments) with less than 1% organic matter. Studies were conducted under no -till methods. Annual rye (Secale cereale L.) was planted as a cover crop during mid-December over the entire experimental area. The rye was allowed to grow until treated with glyphosate 5 weeks prior to planting. When desiccation was complete, t he cov er crop was either left st anding, rolled in the direction of future planting with a tractor -powered implement, or roto -tilled to expose bare soil This location had a severe infestation of ALS -resistant Palmer amaranth (20 to 40 plants per m2). The experimental design was a split -plot with cover crop as the main effect and herbicide as the sub-split effect Herbicide treatments w ere arranged in a randomized complete block design within each whole plot with four replications. Plot size was 3.0 m by 7 .6 m with 76.2 cm row spacing. All studies received irrigation, fertility, fungicide, and insecticide treatments as recommended by the Florida Cooperative Extension Service. Sun Oleic 97R was planted May 21, 2008 and Florida 07 was planted May 15, 20 09 in a twin-row configuration. Peanut s eeds were planted at a depth of 5 cm

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16 with a seeding rate of 17 seeds per meter of row (Wright et al. 2006). Each year aldicarb wa s applied in furrow at 3.2 kg/ha. Within each c over crop scenario, preemergence herbi cides were applied within 0 to 3 days after planting (DAP) Herbicide treatments consisted of pendimethalin (1.07 kg/ha), metolacholor (1.35 kg/ha), flumioxazin (0.10 kg/ha), norflurazon (1.34 kg/ha) In addition, an a t -crack (AC) [7 10 days after emergence (DAE)] application of metolachlor (1.35 kg/ha) + paraquat (0.21 k g/ha) + 2, 4-DB (0.25 kg/ha) was applied. All experimental treatments were applied with a CO2-pressurized plot sprayer calibrated to deliver 187 L/ha. Annual rye was harvested in 0.25 m2 areas randomly throughout the experimental area both years; this data was used to calculate dry biomass kg ha1. Weed counts were started one week after herbicide application and subsequent counts were recorded weekly. These counts were taken from the m iddle of each plot in an area measuring 3.0 m by 0.76 m until threshold was achieved. A threshold of 1 PA per meter of row was calculated based on research of Burke et al. ( 2007 ) which showed a yield loss of approximately 30% at this density. If the thr eshold was not reached prior to crop canopy closure, the day of the last evaluation was used as the days to threshold datum. Linear interpolation was used to calculate days to thresh old for each treatment. D ata were subjected to analysis of variance usi ng the PROC MIXED procedure of SAS (2008) to test for treatment effects and interactions. Means were separated using Fishers protected Least Sig nificant Difference (LSD) at p 0.05.

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17 Results and Discussion Statistical analysis detected a significant treatment by year interaction, so data will be presented by year. In 2008, the main effect of cover crop was not significant and herbicide treatment was pooled across cover crop. In 2009, both cover crop and herbicide s were significant and all data are presented accordingly. In 2008, dry weight of annual rye cover crop was 2067 kg ha1 at the time of planting. For pendimethalin and norflurazon treatements, PA reached the 1 plant per meter threshold within 3 and 8 days after application, respectively, compared to the untreated control which reached threshold at 2 days (Table 1-1). This lack of control was expected with norflurazon as the label indicates Amaranthus spp. will only be suppressed (Anonymous 2009 a ). The label f or pendimethalin, indicates tha t PA will b e controlled (Anonymous 2008), but Grichar (2008) also reported that pendimethalin applied PRE in peanut provided less than 42% control of PA approximately 10 weeks after planting. Metolachlor applied PRE suppressed PA for 22 days after applic ation while metolachlor + paraquat + 2, 4-DB ap plied AC reached threshold 54 days after application. The application of f lumioxazin PRE resulted in 67 days to threshold, the greatest number of days until thres hold was met for all treatments. In 2009, ther e was a significant cover crop by herbicide treatment interaction (Table 12) Annual rye dry biomass at the time of planting, was 2436 kg ha1 which was similar to 2008 Control with p endimethalin and norflurazon was comparable to that observed in 2008 only delaying PA threshold < 3 days after applicati on (Table 1 -2 ). Metolachlor applied PRE was not as effective as 2008 only delaying threshold by 0.5 days. This was unexpected considering that previous research has shown metolachlor applied PRE in peanut controlled PA 95% and 90% (Grichar 1994; Grichar 2008).

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18 F lumioxazin provided the greatest duration of PA control, nearly 17 days without cover crop and over 34 days when in conjunction with a standing rye cover crop. Flumioxazin applied PRE at 0.10 kg ha1 was found to control PA 85% in peanut 10 weeks after planting (Grichar 2008). Significant differences were found between standing, rolled, and no cover for the metolachlor + paraquat + 2, 4-DB AC treatment. Resulting in a standing cover crop exte nding days to threshold by 12 days compared to the rolled cover crop (Table 12 ). Days to threshold decreased for all treatments in 2009 compared to 2008. This could have been due to the increased rainfall received in 2009, during the month after her bicide application and lack of rainfall in the months that followed, compared to 2008 (T able 13 ). In general, an annual rye cover crop at < 2500 kg ha1 of dry biomass, did not significantly increase the days to threshold for most treatments. But studies that produced cover crop biomass > 7500 kg ha1 reported reduced numbers of weeds compared to no cover treatments (Reddy 2001, Reddy 2003 ). Pendimethalin and norflurazon are not reliable control options for the high PA populations encounter ed in this trial These herbicides could possibly control or suppress PA if populations are low. The s e data indicate flumioxazin applied PRE would require a POST application at an average of 1 6 to 67 days after application. Metolachlor + paraquat + 2, 4-DB applied AC provided an average of 23 days until threshold was achieved. It is unknown why delaying metolachlor application by 7 days (PRE vs AC) so greatly influences PA control. However, simi lar results have been observed for the control of tropical spider wort ( Commelina benghalensis ) in peanut ( Flanders and Prostko 2003 ). Regardless of whether metolachlor or flumioxazin is applied, it would be necessary to

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19 start a weekly scouting regimen 3 to 4 weeks after application in order to ensure that timely POST applications can be made to control ALS -resistant PA in peanut.

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20 Table 1 1 Influence of preemergence and post herbicides on Palmer amaranth days to threshold in 2008. Herbicide Rate Timing Days to Treatment kg/ha of trt. 1 Threshold 2 flumioxazin 0.10 PRE 67 a 3 pendimethalin 1.07 PRE 3 d norflurazon 1.34 PRE 8 d metolachlor 1.35 PRE 22 c metolachlor + 1.35 AC 54 b paraquat + 0.21 AC 2, 4 DB 0.25 AC untreated 2 d 1 Timing of herbicide treatments (trt) ar e as followed: PRE=preemergence, AC=At -crack 2 Number of days requ ired to achieve a threshold of 1 Palmer amaranth per meter of crop row 3 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test

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21 Table 1 2 Influence of cover crop scenarios none, rolled and standing combined with preemergence and post emergence herbicides on Palmer amaranth days to threshold in 2009. Herbicide Rate Timing Treatment kg/ha of trt. 1 None 2 Rolled Standing flumioxazin 0.10 PRE 16 3 a 4 A 5 27 aA 35 aA pendimethalin 1.07 PRE 0.3 aC 0.2 aC 0.2 aC norflurazon 1.34 PRE 2 aC 4 aBC 2 aC metolachlor 1.35 PRE 0.1 aC 0.5 aC 1 aC metolachlor + 1.35 AC 6 aB 9 abB 21 bB paraquat + 0.21 AC 2, 4 DB 0.25 AC untreated 0.1 aC 0.1 aC 0.3 aC 1 Timing of herbicide treatments (trt) ar e as followed: PRE=preemergence, AC=At -crack 2 Cover crop scenario.3 Number of days requ ired to achieve a threshold of 1 Palmer amaranth per meter of crop row 3 Values reflect the mean of 4 replications. 4Means within a row followed by lower case letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test .5 Means within a column followed by upper case letters are significantly different from each other at the 0.05 level acc ording to Fis hers Least Significant Difference (LSD) test

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22 Table 1 3 Monthly average of rainfall (mm) for May through August at Sandlin farm in 2008 and 2009. Year May June July August ---------------------------rainfall (mm) ---------------------------2008 (YR1) 4.32 243.59 23 6.47 300.99 2009 (YR2) 190.50 74.17 143.76 204.47

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23 CHAPTER 2 EVALUATION OF FOMESAFEN HERBICIDE FOR ALS -RESISTANT PALMER AMARANTH CONTROL AND EFFECT ON PEANUT INJURY/YIELD Introduction Palmer amaranth (PA) ( Amaranthus palmeri S. Wats) is a dioecious C4 summer annual that originates from the southwestern United States and Mexico (Ehleringer 1983; Steckel 2007). Currently in peanut, PA is consi dered a troublesome weed in Florida, Georgia, and South Carolina (Webster 2005) PA can be difficult to control because of its prolific seed production (Sellers et al. 2003; Keely et al. 1987) and aggressive growth habit s (Horak and Loughin 2000) The growth habits of PA combined with ideal growing conditions increase its ability to compete with most row crops. In corn ( Zea mays L.), PA populations of 0.5 to 8 plants m1 of row reduced yields 11 to 91% respectively, (Massinga et al. 2001; Massinga and Currie 2002) an d soybean [ Gylcine max (L.) Merr.] yield was reduced 17 to 68% from 0.33 to 10 PA plants per m1 of row, respectively (Klingman and Oliver 1994). Rowland et al. (1999) reported cotton ( Gossypium hirsutum L.) lint yield was reduced 92% at PA densities of 8 plants per m1 and Smith et al. (2000) found that PA reduced stripper harvesting time of cotton 2to 3.5fold. PA reduced peanut pod weight linearly with each gram increase of one PA per meter of row (Burke et al. 2007) This resulted in a predicted peanut yield loss of 28% for one PA plant per meter of crop row (Burke et al. 2007). Acetolactate synthase (ALS) -inhibiting herbicides suppress or control susceptible plants by inhibiting acetolactate synthase, an essential enzyme in the biosyn thesis of the branched chain amino acids (Shaner 1991; Saari et al. 1994). Advantages of these herbicides include low use rates, low toxicity, wide crop selection, high efficacy, and

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24 cost effectiveness (Saari et al. 1994). In 1996 imazapic was registered for use in peanut. Imazapic effectively controls PA postem ergence (POST) (Grichar 1997; Grichar 2007) with little to no visual injury to peanut (Dotray et al 2001; Matocha et. al. 2003). But repeated use of ALS inhibiting herbicides for weed control in m any cropping systems has resulted in the selection of ALS -resistant PA. ALS -resistant PA has been confirmed in Arkansas, Florida, Georgia, Kansas, Mississippi, North Carolina, South Caroli na, and Tennessee (Heap 2009). The use of contact herbicides in peanut was common before the registration of imazapic (G.E. MacDonald personal communication). Lactofen and aciflurofen both protoporphyr inogen oxidase (PPO) inhibitors have been shown to provide > 90% PA control in peanut (Grichar 1997). However, thes e herbicides have limited soil activity and do not provide residual control of PA. Flumioxazin, also a PPO inhibiting herbicide, has significant soil residual activity which increases duration of weed control. Experiments conducted in Alabama reported th at flumioxazon applied in peanut controlled PA > 92% (Grey and Wehtje 2005), but this herbicide can only be applied preemergence (PRE) in peanut (Anonymous 2005 ). Therefore, lack of rainfall after application can negate the effectiveness of flumioxazin an d require the use of other POST herbicides. Fomesafen a PPO inhibiting herbicide, i s registered for POST use in soybean (Anonymous 2009 b ) and as a 24c label for early preplant use in cotton (Anonymous 2009c ). It has significant soil activity, with an ave rage field half -life of 100 days (Wauchope et al. 1992). Studies have found that fomesafen will effectively control PA even those resistant to glyphosate and ALS -inhibiting herbicides (Bond et al. 2006;

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25 Norsworthy et al. 2008). PPO -inhibiting herbicides cause phytotoxicity when applied POST on tolerant plants and i njury or yield loss is a concern. Previous research has shown that fomesafen injury on soybean (6% to 11%) is consistently less injurious than acifluorfen or lactofen (15% to 32%) (Higgins et al. 1988). F om esafen is currently not registered in peanut and little is published concerning its effect on peanut PA infestations and the selection of ALS -resistant biotypes have created a serious problem in the southern peanut growing region. PA has the ability to significantly reduce peanut yields ; thus incorporation of new herbicides that can be integrated into existing weed management programs is vital to the success and future of peanut production in the southern United States. Therefore, the obj ectives of our research were as follows: 1) determ ine whether fomesafen can provide PA control in peanut; 2) determine injury and yield loss to peanut from fomesafen applications; and 3) determine an herbicide management program that includes fomesafen that would best fit into southeastern peanut production system s Materials and Methods Field studies were conducted in 2008 and 2009 at the Plant Science Research and Education Unit (PSREU) in Citra, Florida on a Sparr fine sand (loamy, siliceous, hyperthermi c Grossarenic paledult) with 1% organic matter and at Sandlin farms near Williston, Florida on a Candler fine sand (hyperthermic, uncoated Typic Quartzipsamments) with % organic matter. Studies at the PSREU were conducted under conventional -tillage methods as a weed free experiment and at Sandlin farms under no -till conditions as a weedy experiment The Sandlin farm location had a severe infestation of ALS -resistant Palmer amaranth (20 to 40 plants per m2).

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26 Plot size was 3.0 m by 7.6 m on 76.2 cm row spacing. All studies received irrigation, fertility, fungicide and insecticide treatments as recommended by the Florida Cooperative Extension Service. Georgia Green was planted April 23, 2008 and April 22, 200 9 at the PSREU in a single-row configuration. Sun Oleic 97R was planted May 21, 2008 and Florida 07 was planted May 15, 2009 at the Sandlin farm in a twinrow configuration. Seeds were planted at a depth of 5 cm with a seeding rate of 17 seeds per me ter of row (Wright et al. 2006). Each year aldicarb was applied in furrow at 3.2 kg /ha. The experimental area at the PSREU received a preemergence broadcast applic ation of diclosulam (0.42 kg/ha) + pendimethalin (0.92 kg/ha), and a postemergence applicat ion of imazapic (0.07 kg/ha). Supplemental handweeding was performed as needed to maintain weed-free conditions throughout the growing season at the PSREU Only herbicide treatments (with no hand weeding) were applied at the Sandlin Farm site in order t o document PA control. Fomesafen Tolerance Herbicide treatments consisted of fomesafen alone at 0.21, 0.28, 0.42, 0.56 kg/ha applied PRE (0 3 DAP), At -crack (AC) [7 -10 days after emergence (DAE)] POST (21 -28 DAE), as well as flumioxazin applied PRE at 0.03, 0.07 and 0.14 kg/ha. At the Sandlin Farm site, PA was not present during the PRE application and was approximately 5 cm for the AC application and 15 cm for the POST application. Fomesafen Management Herbicide treatments consisted of fomesafen alon e at 0.21, 0.28, 0.42, 0.56 kg/ha applied PRE (03 DAP), At -crack (AC) [7 -10 days after emergence (DAE)], POST (21 -28 DAE), as well as flumioxazin applied PRE at 0.07 and 0.14 kg/ha. T hese treatments were followed by or coupled with a POST application of

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27 paraquat (0.21 kg/ha) + bentazon (0.56 kg/ha) + 2, 4 -DB (0.25 kg/ha). At the Sandlin Farm site, PA was approximately 5 cm tall for the AC application and 15 cm tall for the POST application. All experimental treatments were applied with a CO2pressurized sprayer calibrated to deliver 187 L/ha. A nonionic surfactant at 0.125% (v/v) was included with all POST and AC treatments. Visual estimates of peanut injury were recorded 7, 14, 28 DAT and weed control (Sandlin farm ) were recorded 14, 28, 56 days after tr eatment (DAT). Foliar necrosis, chlorosis, and plant stunting were evaluated using a scale of 0 to 100% with 0 = no injury or control and 100 = crop death or complete weed control (Frans et al. 1986). At Citra days to canopy closure was recorded until s oil was not evident between the two center plot rows. The Hull -Scrape method was used with pods from non-treated peanut plots to determine maturity before harvest ( Williams and Drexler 1981). The center two rows of each plot were dug by a conven tional di gger -shaker inverter and peanuts allowed to field dry approximately 3 days Peanut was harvested by commercial ha rvesting equipment and dried to 9% moisture and weighed to de termine yield on a kg/ha basis. Yield data was only collected at the Citra location. The experimental design for all studies was a randomized complete block with four replications PROC GLM was used to analyze the data for percent PA control, peanut injury, days to canopy closure, and peanut yield (SAS 2008 ). All data were subjected to analysis of variance (ANOVA) to test treatment effects and interactions. Means were separated using Fishers Least Significant Dif ference (LSD) test at p

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28 Results and Discussion Fomesafen Alone ANOVA detected significant differences between herbicide treatment by year and treatment by timing. Therefore, no da ta were pooled and will be presented by year and treatment by timing. Preemergence (PRE) control data was not collected in 2008 because of application error. Peanut toleranc e In 2008, n o visual injury was observed for all fomesafen and flumioxazin treatments applied PRE (Table 2 -1) At -crack (AC) and postemergence (POST) applications of fomesafen resulted in peanut injury that ranged from 8% to 20% 7 days after treatment (DAT) and 2% to 9% 14 DAT. By 28 DAT, no peanut injury was o bserved f r om fomesafen applied AC and POST regardless of application rate. Canopy closure data was also collected as a measure of peanut vine stunting and recovery. Days to canopy closure was increased, compared to the untreated, for most fomesafen applications. But all peanut canopies closed within 11 days of the untreated contr ol regardless of fomesafen application timing or rate. In 2009, visual injury from fomesafen and flumioxazin applied PRE was not observed (Table 2-2). AC applications were similar to that of 2008 with the exception of the lowest rate of fomesafen, 0.21 kg ha1, which increased from 8% in 2008 to 15% in 2009 7 DAT and 6% to 10% 14 DAT. In 2009, POST applications ranged from 0% to 13% percent peanut injury 7 DAT. No injury was observed at 14 and 28 DAT. Canopy closure was found to be significant f or most treatments, but all closed within 8 days of the untreated c ontro l. When compared to the untreated control y ield was not significantly reduced for any treatment regardless of visual injury for AC and POST applications

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29 Fomesafen applied PRE, AC, and POS T did not decrease yield significantly, compared to the untreated control either year (Tables 21 and 2 -2) Grichar (1992), however, stated that fomesafen applied PRE at 0.43 kg ha1 decreased yield by 30%. PRE applications of fomesafen and flumioxazin did not produce any vi sual injury in either year, however, AC and P OST applications of fomesafen caused visual injury that ranged from 0% to 10 % 14 DAT. F omesafen applied POST in soybean at 0.3 and 0.6 kg ha1 resulted in injury that ranged fr om 2% to 11% (Higgins et al. 198 8). Despite visual injury and a delay in canop y closure, AC and POST applications did not reduce yield significantly, compared to the control. Although previous experiments suggests that yield reduction is possible, t hese data suggest that fomesafen can be ap plied PRE, AC, or POST without s ignificant risk of peanut yield loss. Palmer amaranth control In 2008, fomesafen at all rates applied AC to 2.5 to 5.5 cm tall Palmer amaranth (PA) provided control 14 DAT, 84% 56 DAT (Table 2 -3). Fomesafen applied POST at rate s of 0.21 and 0.28 kg ha1 controlled 15 to 20 cm tall PA, 65% and 50% 14 DAT, 45% and 25% 28 DAT, 13% and 0% 56 DAT. Conversely, fomesafen applied POST at increased rates, 0.42 and 0.56 kg ha1, controlled PA T. Control of PA was 0.56 kg ha1 of fomesafen was necessary to reach > 80 % control 56 DAT. Control o f PA decreased over time for all treatments in 2009. PRE applications of fo mesafen and flumioxazin resulted in 94% or greater control 14 DAT (Table 2-4). Flumioxazin applied PRE at rates of 0.07 and 0.14 kg ha1 controlled PA but decreased to 78% and 86% control 56 DAT. Fomesafen applied PRE did not

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30 provide > 59% PA control 56 DAT, regardless of application rate. Lower rates of fomesafen at 0.21 and 0.28 kg ha1 applied AC to PA, at 2.5 to 5 cm provided control of 83% and 86 % 14 DAT respectively AC fomesafen applications at 0.42 and 0.56 kg ha1 controlled PA 93% and 97% 14 DAT, 77% and 78% 28 D AT, 46% and 53% 56 DAT. By 28 DAT, control with both rates decreased to 55% and 56% POST applications of fomesafen at 0.21, 0.28, and 0.42 kg ha1 to PA, at 10 to 15cm, provided < 36% PA control 28 DAT. Fomesafen applied POST at 0.56 kg ha1 controlled PA 79% 28 DAT but all rates showed < 11% control 56 DAT Fomesafen applied AC at rates of 0.21, 0.28, and 0.42 kg ha1 in 2008 controlled PA 86%, 89%, and 92% 28 DAT but in 2009 control was only 55%, 56%, and 78% 28 DAT. POST applications of fomesafen, excluding 0.56 kg ha1, resulted in 45%, 25%, and 80% control in 2008 compared with 11%, 25%, and 36% co ntrol in 2009, at 28 DAT. In a study conducted by Starke and Oliver (1998) fomesafen at 0.21 and 0.42 kg ha1 controlled PA 32% and 37% 28 DAT. Furthermore, a study conducted in Kansas controlled PA with fomesafen applied at 0.28 kg ha1, 74% to 76% (Sweat et al. 1998). The inconsistencies in control of PA from different years and studies coul d be attributed to weather conditions, seed population, and PA size at application. This indicates that fomesafen can be a highly effective herbicide for ALS resistant PA, but that control failures may occur. In conclusion, foliar injury of peanut due to AC and POST applications of fomesafen did not negatively affect yield. However, fomesafen applied PRE at all rates, AC at 0.42 and 0.56 kg ha1, and POST at 0.28, 0.42, and 0.56 kg ha1 were found to reduce yields in Texas (Gilbert et al. 2009). Also, in 2008 higher rates of fomesafen

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31 applied AC at Sandlin farm caused significant peanut injury at 42 DAT (Table 25 ). But peanut injury was not detected 28 DAT for any fomesafen treatment in 2009 (data not shown). The reasons for these inconsistencies in peanut injury and yield loss are unknown The control of PA was at 56 DAT when fomesafen was applied AC in 2008. However, in year two PA control was applications of 0.56 kg ha1 provided DAT. Generally, PRE applications of fomesafen at 0.42 and 0.56 controlled PA up to 28 DAT. But PA control for all PRE fomesafe n rates at 56 DAT were < 57%. Growers need to be aware that different environmental conditions may cause negative effects from f omesafen applied in peanut base d studies conducted by Gilbert et. al (2009) Fomesafen Management Statistica l analysis detected herbicide treatment by year and treatment by timing interactions for percent control and injury. No such interactions were detected for canopy closure and yield. Therefore, canopy closure and yield data were pooled across years, but PA control and peanut injury data were presented separately by year. Peanut Tolerance. In 2008, injury from PRE and POST treatmen ts ranged from 21% to 26% 7 DAT (Table 2 6 ). AC treatments ranged from 38% to 41% injury 7 DAT. Injury declined to a range of 3% to 16% injury for all treatments 14 DAT and no visual injury was observed 28 DAT. In 2009, injury ranged from 26% to 43% for all treatments 7 DA T (Table 2 7 ). PRE and POST applications resulted in injury at 14 DAT from 8% to 10% while there was no injury observed for AC treatments. Injury was not observed for all treatments 28 DAT in 2009.

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32 In 2008 and 2009, yield was not significantly reduced c ompared to the untreated control. Canopy closure was delayed for all treatments but the greatest delay was within 9 days of the untreated control (Table 2 8 ). This study found that peanut yield was not significantly reduced after a PRE application of flum ioxazin or fomesafen, followed by a POST application, of paraquat. These data agree with research conducted by Grey and Wehtje (2005) and Askew et al. (1999) who found that the use of a PRE herbicide combined with a POST application of a contact herbicide resulted in no significant peanut yield r eductions. Other research has shown that paraquat applied POST did not reduce yield when foliar peanut injury occurred (Wehtje et al. 1986; Wilcut et al. 1989). These data, compared to the current experiment, found that foliar injury and canopy closure is not a consistent indicator for peanut yield loss. Palmer amaranth control In 2008, control of PA for all treatments ranged from 90% to 100% 28 DAT and 85% to 100% 56 DAT (Table 2-9 ) In 2009, PA control ranged from 86% to 99% 28 DAT and remained consistent 56 DAT, at a range of 86% to 97% (Table 210 ). Control for both years was good to excellent, with a slight decrease overall in 20 09. This could be attributed to differing weather conditions from year to yea r. In general, control of PA was increased with the increase of fomesafen rate, although this increase in control was minimal. The control of PA was flumioxazin was applied PRE followed by a POST treatment of paraquat + bentazon + 2,4-DB. Simi lar results were found in Georgia with PA being controlled application of flumioxazin PRE followed by paraquat + bentazon POST (Grey and

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33 Wehtje 2005). PA was controlled application of fom easfen or flumioxazin followed by a POST application will increase control of PA.

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34 Table 2 1 Influence of fomesafen and flumioxazin on % injury, days to row closure, and yield of peanut in 2008 at Citra, FL (weed-free) Herbicide Rate Timing -----------% injury 1 ---------Days to Closure 2 Yield Treatment 3 kg/ha of trt. 3 7 DAT 4 14 DAT 28 DAT 76.2 cm rows % UTC 5 fomesafen 0.21 PRE 0e 6 0d 0a 62c e 109a c fomesafen 0.28 PRE 0e 0d 0a 67a c 100c f fomesafen 0.42 PRE 0e 0d 0a 65a d 111ab fomesafen 0.56 PRE 0e 0d 0a 69ab 106a d flumioxazin 0.03 PRE 0e 0d 0a 67a c 102a f flumioxazin 0.07 PRE 0e 0d 0a 58e 109a c flumioxazin 0.14 PRE 0e 0d 0a 64b e 112a fomesafen 0.21 AC 8d 2cd 0a 65a d 104a e fomesafen 0.28 AC 15bc 5bc 0a 67a c 102a f fomesafen 0.42 AC 17ab 5bc 0a 71a 101b f fomesafen 0.56 AC 20a 7ab 0a 71a 92f fomesafen 0.21 POST 13c 9a 0a 71a 100c f fomesafen 0.28 POST 16a c 8ab 0a 71a 101b f fomesafen 0.42 POST 15bc 9a 0a 71a 98d f fomesafen 0.56 POST 18ab 9a 0a 71a 93ef untreated 0e 0d 0a 60de 100c f 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant death. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Timing of tr eatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence. 4 DAT = days after treatment. 5 Percent of the untreated yield (3056 kg/ha) 6 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test *A non -ionic surfactant at 0.125% v/v was used for all AC and POST applications.

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35 Table 2 2 Influence of fomesafen and flumioxazin at varied rates on % injury, days to row closure, and yield of peanut in 2009 at Citra, FL (weed-free) Herbicide Rate Timing -----------% injury 1 ---------Days to Closure 2 Yield Treatment 3 kg/ha of trt. 3 7 DAT 4 14 DAT 28 DAT 76.2 cm rows % UTC 5 fomesafen 0.21 PRE 0g 6 0c 0a 65cd 110a c fomesafen 0.28 PRE 0g 0c 0a 67b c 98b e fomesafen 0.42 PRE 0g 0c 0a 64d 90de fomesafen 0.56 PRE 0g 0c 0a 67b c 106a d flumioxazin 0.03 PRE 0g 0c 0a 64d 109a c flumioxazin 0.07 PRE 0g 0c 0a 69a c 108a c flumioxazin 0.14 PRE 0g 0c 0a 66b c 111ab fomesafen 0.21 AC 15cd 6b 0a 68a d 100b e fomesafen 0.28 AC 16bc 6b 0a 64d 122a fomesafen 0.42 AC 19ab 8b 0a 69a c 105b c fomesafen 0.56 AC 20a 10a 0a 69a c 105b c fomesafen 0.21 POST 5f 0c 0a 70ab 109a c fomesafen 0.28 POST 10e 0c 0a 72a 114ab fomesafen 0.42 POST 10e 0c 0a 72a 94c e fomesafen 0.56 POST 13de 0c 0a 72a 84e untreated 0g 0c 0a 64d 100b e 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant death. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Timing of treatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence. 4 DAT = days after treatment. 5 Percent of the untreated yield ( 2402 k g/ha) 6 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test *A non -ionic surfactant at 0.125% v/v was used for all AC and POST applications.

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36 Table 2 3. Influence of fomesafen and flumioxazin on % control of Palmer amaranth in 2008 at Williston, FL (weedy) Herbicide Rate Timing ---------------------------% control 1 -------------------------Treatment kg/ha of trt. 2 14 DAT 3 28 DAT 56 DAT fomesafen 0.21 AC 96a 4 86ab 84ab fomesafen 0.28 AC 93a 89ab 86ab fomesafen 0.42 AC 98a 92ab 88ab fomesafen 0.56 AC 99a 98a 96a fomesafen 0.21 POST 65b 45c 13d fomesafen 0.28 POST 50c 25d 0e fomesafen 0.42 POST 89a 80b 69c fomesafen 0.56 POST 93a 85b 83b untreated 0d 0e 0e 1 Visual assessment of foliar necrosis, chlorosis, and plant stunting were based on the following scale: 0 = no control; 100 = complete weed control. 2 Timing of treatments (trt) are as followed: PRE=preemergence, AC=At -crack, cm weeds, POST= postemergence cm weeds 3 DAT = days after treatment. 4 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fi s hers Least Significant Differ ence (LSD) test. *A non -ionic surfactant at 0.125% v/v was used for all AC and POST applications.

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37 Table 2 4 Influence of fomesafen and flumioxazin on % control of Palmer amaranth in 2009 at Williston, FL (weedy) Herbicide Rate Timing ---------------------------% control 1 -------------------------Treatment kg/ha of trt. 2 14 DAT 3 28 DAT 56 DAT fomesafen 0.21 PRE 94ab 4 79a c 55cd fomesafen 0.28 PRE 94ab 69cd 33e g fomesafen 0.42 PRE 98ab 81a c 40c e fomesafen 0.56 PRE 99ab 81a c 59bc flumioxazin 0.03 PRE 96ab 83a c 57b d flumioxazin 0.07 PRE 100a 94ab 78ab flumioxazin 0.14 PRE 100a 97a 86a fomesafen 0.21 AC 86ab 55de 26f h fomesafen 0.28 AC 83b 56de 36d e fomesafen 0.42 AC 93ab 78a c 53c e fomesafen 0.56 AC 97ab 77bc 46c f fomesafen 0.21 POST 13d 11gh 0i fomesafen 0.28 POST 49c 25fg 6hi fomesafen 0.42 POST 48c 36ef 11g i fomesafen 0.56 POST 88ab 79a c 11g i untreated 0d 0h 0i 1 Visual assessment of foliar necrosis, chlorosis, and plant stunting were based on the following scale: 0 = no control; 100 = complete weed control. 2 Timing of treatments (trt) are as followed: PRE=preemergence, AC=At -crack, cm weeds, POST= postemergence, 3 DAT = days after treatment. 4 Values reflect the mean of 4 replications. Means within a column followed by different letters are signific antly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test *A non -ionic surfactant at 0.125% v/v was used for all AC and POST applications.

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38 Table 2 5 Influe nce of fomesafen on % injury of Palmer amaranth in 2008 at Williston, FL (weedy) Herbicide Rate Timing --------------------------% injury 1 -------------------------Treatment kg/ha of trt. 2 14 DAT 3 28 DAT 42 DAT fomesafen 0.21 AC 9e 4 2e 0f fomesafen 0.28 AC 11de 10c e 6b d fomesafen 0.42 AC 16dc 34a 25a fomesafen 0.56 AC 19c 41a 27a fomesafen 0.21 POST 12c e 5de 4cd fomesafen 0.28 POST 28b 11cd 5b c fomesafen 0.42 POST 32ab 17bc 13b fomesafen 0.56 POST 36a 34b 11bc untreated 0f 0f 0f 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant death. 2 Timing of treatments ar e as followed: AC=At -crack, POST= postemergence. 3 DAT = days after treatment. 4 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fi s hers Least Sig nificant Difference (LSD) test. *A non -ionic surfactant at 0.125% v/v was used for all AC and POST applications.

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39 Table 2 6 Influence of fomesafen and flumioxazin combined with other postemergence herbicides on % injury of peanut in 2008 at Citra, FL (weed -free) Herbicide Rate Timing ---------------------------% injury 1 -------------------------Treatment kg/ha of trt. 2 7 DAT 3 14 DAT 28 DAT f omesafen 4 0.21 PRE 21b 5 3fe 0a f omesafen 4 0.28 PRE 23b 5d f 0a f omesafen 4 0.42 PRE 22b 8c e 0a f omesafen 4 0.56 PRE 24b 14ab 0a f lumioxazin 4 0.07 PRE 22b 4d f 0a f lumioxazin 4 0.14 PRE 23b 9c d 0a f omesafen 6 0.21 AC 38a 6de 0a f omesafen 6 0.28 AC 41a 5d f 0a f omesafen 6 0.42 AC 40a 6de 0a f omesafen 6 0.56 AC 40a 8c e 0a f omesafen 6 0.21 POST 22b 11a c 0a f omesafen 6 0.28 POST 25b 16a 0a f omesafen 6 0.42 POST 22b 15a 0a f omesafen 6 0.56 POST 26b 16a 0a paraquat + 0.21 POST 25b 7c e 0a bentazon + 0.56 POST 2, 4 DB 0.25 POST untreated 0c 0f 0a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant death. 2 Timing of treatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence. 3 DAT = days after treatment. 4 Treatment was followed by a POST application of paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). 5 Values reflec t the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test 6 Treatment was combined with paraquat (0.21 kg/ ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). *A nonionic surfactant at 0.125% v/v was used for all AC and POST applications.

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40 Table 2 7 Influence of fomesafen and flumioxazin combined with other postemergence herbicides on % injury of peanut in 2 009 at Citra, FL (weed -free) Herbicide Rate Timing ---------------------------% injury 1 -------------------------Treatment kg/ha of trt. 2 7 DAT 3 14 DAT 28 DAT fomesafen 4 0.21 PRE 39a c 5 8a 0a fomesafen 4 0.28 PRE 39a c 10a 0a fomesafen 4 0.42 PRE 38a c 10a 0a fomesafen 4 0.56 PRE 43a 10a 0a flumioxazin 4 0.07 PRE 38b d 10a 0a flumioxazin 4 0.14 PRE 36c e 10a 0a fomesafen 6 0.21 AC 26g 0b 0a fomesafen 6 0.28 AC 29fg 0b 0a fomesafen 6 0.42 AC 34de 0b 0a fomesafen 6 0.56 AC 33ef 0b 0a fomesafen 6 0.21 POST 39a c 9a 0a fomesafen 6 0.28 POST 40a c 10a 0a fomesafen 6 0.42 POST 41ab 10a 0a fomesafen 6 0.56 POST 43a 9a 0a paraquat + 0.21 POST 38b d 10a 0a bentazon + 0.56 POST 2, 4 DB 0.25 POST untreated 0h 0b 0a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant death. 2 Timing of treatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence. 3 DAT = days after treatment. 4 Treatment was followed by a POST application of paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). 5 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test 6 Treatment was combined with paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). *A nonionic surfactant at 0.125% v/v was used for all AC and POST applications.

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41 Table 2 8 Influence of fomesafen and flumioxazin on days to row closure and yield of peanut in 2008 and 2009 at Citra, FL (weed -free) Herbicide Rate Timing Days to Closure 1 Yield Treatment kg/ha of trt. 2 76.2 cm rows % UTC 3 f omesafen 4 0.21 PRE 67c f 5 104ab f omesafen 4 0.28 PRE 68b f 97ab f omesafen 4 0.42 PRE 68b f 108ab f omesafen 4 0.56 PRE 71b 98ab f lumioxazin 4 0.07 PRE 68b f 109ab f lumioxazin 4 0.14 PRE 71b 114a f omesafen 6 0.21 AC 67c f 110a f omesafen 6 0.28 AC 66fg 106ab f omesafen 6 0.42 AC 67c f 103ab f omesafen 6 0.56 AC 69b d 104ab f omesafen 6 0.21 POST 70bc 107ab f omesafen 6 0.28 POST 73a 100ab f omesafen 6 0.42 POST 73a 103ab f omesafen 6 0.56 POST 73a 94b paraquat + 0.21 POST 68b f 105ab bentazon + 0.56 POST 2, 4 DB 0.25 POST Untreated 64g 100ab 1 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 2 Timing of treatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence. 3 Percent of the untreated yield ( Year 1 = 2597 kg/ha, Ye ar 2 = 2800 kg/ha). 4 Treatment was followed by a POST application of paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4 -DB (0.25 kg/ha). 5 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test 6 Treatment was combined with paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). *A nonionic surfactant at 0.125% v/v was used f or all AC and POST applications.

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42 Table 2 9 Influence of fomesafen and flumioxazin combined with other post emergence herbicides on % control of Palmer amaranth in 2008 at Williston, FL (weedy) Herbicide Rate Timing --------------------------% control 1 ------------------------Treatment kg/ha of trt. 2 14 DAT 3 28 DAT 56 DAT f omesafen 4 0.21 PRE 99ab 5 98ab 97a c f omesafen 4 0.28 PRE 100a 98ab 97a c f omesafen 4 0.42 PRE 100a 99a 98ab f omesafen 4 0.56 PRE 100a 100a 98ab f lumioxazin 4 0.07 PRE 100a 100a 99ab f lumioxazin 4 0.14 PRE 100a 98ab 98ab f omesafen 6 0.21 AC 95c 90c 85d f omesafen 6 0.28 AC 98b 90c 85d f omesafen 6 0.42 AC 98b 95b 93c f omesafen 6 0.56 AC 99ab 97ab 95bc f omesafen 6 0.21 POST 100a 100a 100a f omesafen 6 0.28 POST 100a 100a 100a f omesafen 6 0.42 POST 100a 100a 100a f omesafen 6 0.56 POST 100a 100a 99ab paraquat + 0.21 POST 100a 100a 98ab bentazon + 0.56 POST 2, 4 DB 0.25 POST untreated 0d 0d 0e 1 Visual assessment of PA control was based on the following scale : 0 = no control; 100 = complete control 2 Timing of treatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence, 3 DAT = days after treatment. 4 Treatment was followed by a POST application of paraquat (0.21 kg/ha) + bentazon (0. 56kg/ha) and 2, 4 -DB (0.25 kg/ha). 5 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test 6 Treatment was combined with paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). *A nonionic surfactant at 0.125% v/v was used for all AC and POST applications.

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43 Table 2 10 Influence of fomesafen and flumioxazin combined with other post emergence herbicides on % control of Palmer amaranth in 2009 at Williston, FL (weedy) Herbicide Rate Timing --------------------------% control 1 ------------------------Treatment kg/ha of trt. 2 14 DAT 3 28 DAT 56 DAT f omesafen 4 0.21 PRE 97bc 5 91c f 87b f omesafen 4 0.28 PRE 99b 92b f 90ab f omesafen 4 0.42 PRE 97bc 90d f 87b f omesafen 4 0.56 PRE 98a c 89ef 88ab f lumioxazin 4 0.07 PRE 99ab 96a d 94ab f lumioxazin 4 0.14 PRE 100a 98ab 97a f omesafen 6 0.21 AC 100a 97a c 87b f omesafen 6 0.28 AC 100a 97a c 90ab f omesafen 6 0.42 AC 100a 99a 95ab f omesafen 6 0.56 AC 100a 97a c 94ab f omesafen 6 0.21 POST 98a c 93a e 93ab f omesafen 6 0.28 POST 97bc 93a e 92ab f omesafen 6 0.42 POST 98a c 97a c 92ab f omesafen 6 0.56 POST 99ab 99a 97a paraquat + 0.21 POST 96c 86f 86b bentazon + 0.56 POST 2, 4 DB 0.25 POST untreated 0d 0g 0c 1 Visual assessment of PA control was based on the following scale : 0 = no control; 100 = complete control 2 Timing of treatments are as followed: PRE=preemergence, AC=At -crack, POST= postemergence, 3 DAT = days after treatment. 4 Treatment was follow ed by a POST application of paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). 5 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 lev el according to Fis hers Least Significant Difference (LSD) test 6 Treatment was combined with paraquat (0.21 kg/ha) + bentazon (0.56kg/ha) and 2, 4-DB (0.25 kg/ha). *A nonionic surfactant at 0.125% v/v was used for all AC and POST applications.

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44 C HAPTER 3 THE INFLUENCE OF CARRIER VOLUME, NOZZLE TYPE, AND PLANT HEIG HT ON CONTROL OF PALMER AM AR ANTH IN PEANUT Introduction In peanut, Palmer amaranth (PA) ( Amaranthus plamer S. Wats) is considered a troublesome weed in Florida, Georgia, and South Carolina (Webster 2005). PA can also be found throughout the peanut producing areas of the southeastern and southern United States (Gleason and Cronquist 1991; Horak and Loughin 200). PA, a dioecious C4 plant, is a summer annual that is native to the southwestern United States and Mexico (Byrson and DeFelice 2009; Ehleringer 1983; Steckel 2007), where it thrives at high er temperatures. High temperatures are also characteristic of t he s outhern peanut producing region during peanut growth and maturity. The r apid growth and tremendous seed production of PA (Sellers et al. 2003; Keely et al. 1987) combined with growing conditions found in the southeast that make i t a competitive weed i n peanut. In 1996 imazapic (Cadre), an acetolactate synthase (ALS) -inhibitor, was register ed for use in peanut. Imazapic is systemic within the plant and effectively controls PA when applied postemergence (POST) in peanut (Grichar 1997; Grichar 2007). R epeated use of ALS inhibitors in peanut and other row crops has lead to wide -spread ALS resistance Currently, ALS resistant PA can be found in Arkansas, Florida, Georgia, Kansas, Mississippi, North Carolina, South Carol ina, and Tennessee (Heap 2009). The prevalence of ALS -resistant PA in peanut ha s forced producers to reconsider POST contact herbicides, such as diphenlyether herbicides, which were commonly used before the registration of imazapic (G.E. MacDonald personal communication). But over the pa st decade s pray technology has evolved as well. The high cost of

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45 transporting water and the need to cover more hectarage per fill up has caused many producers to use lower spray volumes (Etheridge 1999). Additionally, sprayers are traveling at faster speed than in the past, resulting in greater drift potential. To counter this, many have switched fr om the use of standard flat fan (FF) nozzles (such as TeeJet XR) to drift reducing nozzles (like the TeeJet Air Induction). Air induction (AI) nozzles operat e by seeding air into the spray stream just prior to the exit orifice (Piggot and Matthews 1999). Etheridge et al. (1999) found that AI nozzles produced larger droplets compared to conventional FF nozzles at a given pressure. Studies have indicated that large droplet producing nozzles are capable of reducing drift > 75% (Miller and Lane 1999; Ellis et al 2002). Although larger droplets reduce drift, spray coverage is also sacrificed. Knoche 1994 considered that smaller droplets from FF nozzles to be mor e effective than larger droplets when applying POST herbicide s at a constant carrier volume. Recent research found that control of Abutilon theophrasti and Chenopodium album with fomesafen, a contact herbicide, was improved as carrier volume was increased for both FF and AI nozzles (Sikkema et al. 2008). However, Ramsdale and Messersmith (2001) found that paraquat provided effective grass control regardless of sprayer nozzle type and carrier volume. Studies have shown that nozzle type, water carrier volum e, and spray pressure is herbicideand weed species -specific (Brown et al. 2007; Sikkema et al. 2008). Local peanut producers have reported PA control failures with the application of contact herbicides with AI nozzles. It was assumed that incomplete coverage led to these failures. However, PA size at time of application may also have been a contributing factor.

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46 It is currently unknown how application practi ces affect PA control with cont act herbicides. Since most contact herbicides are of limited effectiveness on PA, it is important to know if altering spray droplet size and carrier volume to improve overall spray coverage will improve the consistency of control. Therefore, a study was conducted to evaluate the efficacy of lactofen, a contact herbicide, on PA at two stages of growth when applied with FF and AI nozzles at three different carrier volumes. Materials and Methods Spray Coverage Study Tre atments consisted of XR Teejet (FF) nozzles (Teejet FF nozzle tips; Spraying Systems Company, Wheaton, IL, USA) and AI Teejet nozzles (Teejet AI nozzle tips; Spraying Systems Company, Wheaton, IL, USA) that were calibrated to deliver application volumes of 94, 187, 281 L ha1. The sprayer was equipped with each series of nozzles and calibrated for each d esired carrier volume. Water was sprayed with each nozzle/volume combination over water sensitive cards to generate droplet distribution. Each card was placed parallel to the ground and 50 cm below the spray nozzles. All water sensitive cards were evalu ated with a high resolution flat -bed scanner. Percent coverage was calculated by a color identification computer software program, WinCam. Experimental design was a randomized complete block with four replicates. These data were subjected to analysis of variance using PROC GLM to determine treatment effects and interactions (SAS 2008). Means were separated using Fishers Least Significant Difference (LSD) test at p Field Study Field studies were conducted in 2008 and 2009 at Sandlin Farms near Wi lliston, Florida on a Candler fine sand (hyperthermic, uncoated Typic Quartzipsamments) with

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47 less than 1 % organic matter. Studies were conducted under no-till methods. This location had a severe infestation of ALS resistant Palmer amaranth (20 to 40 plant s per m2). Plot size was 3.0 m by 7.6 m on 76.2 cm row spacing. Studies received irrigation, fertility, fungicide and insecticide treatments as recommended by the Florida Cooperative Extension Service. Sun Oleic 97R was planted May 21, 2008 and Flor ida 07 was planted May 15, 2009 in a twin -row configuration. Peanut s eeds were planted at a depth of 5 cm with a seeding rate of 17 seeds per meter of row (Wright et al. 2006). Each year aldicarb was applied in furrow at 3.2 kg/ ha. The experiment was a multi -factorial design arranged in a randomized complete block with nozzle type, carrier volume, and weed size as factors A series of XR Teejet (FF) nozzles and AI Teejet nozzles were used to obtain the desired application volumes. The timing of herbicide applications were based on PA height ranges of 5 to 10 c m and 15 to 20 c m Height measurements were recorded randomly in each replication until the desired height range was ach ieved. Treatments were applied with a CO2-pressurized sprayer calibrated to deliver 94, 187, or 281 L ha1. L actofen was applied at 0.21 kg ha1 + crop oil c oncentrate 1% (v/v) Visual estimates of percent PA control were recorded 14, 28, 42 days after t reatment (DAT). Foliar necrosis, chlorosis, and plant stunting were evaluated using a scale of 0 to 100% with 0 = no control and 100 = complete weed control (Frans et al. 1986). All data were subjected to an analysis of variance a nd analyzed using the PR OC GLM procedure of SAS ( 2008) to test treatment effects and interactions. Means were separated using Fishers Least Significant Dif ference (LSD) test at p

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48 Data was not collected in 2009 because of extreme variations in PA emergence and height thr oughout the experimental area. This was due to abnormally high rainfall in the first fo ur weeks after peanut planting that was followed by 5 weeks of drought Results and Discussion Quantifying Spray Coverage There were significant interactions between nozzle type and carrier volume which prevented pooling of data. At a carrier volume of 94 L ha1, 21% coverage was achieved with the use of flat fan (FF) nozzles but coverage was only 11% with air induction (AI) nozzles (Figure 31). AI and FF nozzles applied at 187 L ha1 covered an area of 28% and 47%, respectively. Increased carrier volume of 281 L ha1 reached coverage of 55% for AI nozzles and 69% FF for nozzles. At 94 and 187 L ha1, coverage was almost double for the FF verses the AI nozzle. No d ifferences were observed between percent coverage for FF at 187 L ha1 and AI at 281 L ha1. Though drift potential is great er for FF nozzles, the same spray coverage can be achieved, relative to AI nozzles, while utiliz ing 1/3 less water. These data matc h, in part, with that reported by Ramsdale and Messersmith (2001) At both 94 and 187 L ha1, spray coverage with FF nozzles is very similar to what is reported here. However, the data reported for AI nozzles at similar carrier volumes, was near double that reported in this experiment. The reason for these differences is unknown. Field Study There were no significant interactions between nozzle type and Palmer amarant h (PA) control. Therefore, nozzl e type data were pooled and analyzed for differences among carrier volumes and PA heights.

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49 Lactofen applied 22 days after peanut plantin g to PA at 5 to 10 cm, resulted in no significant differences between carrier volume and sprayer nozzle type (Table 3 1) Control of PA was consistent and ranged from 99% to 100% for all rating dates. PA control persisted greater than 42 days after application. However, as PA size increased to 15 to 20 cm in height, significant differences were detected between carrier volumes. Lactofen applied at a carrier volume of 94 L ha1, controlled PA 84% 14 DAT (Table 32). This was 7% less control than provided by carrier volumes of 187 and 281 L ha1. Control continued to decline for the 94 L ha1 applica tion and PA control was 82% and 75% at 28 DAT and 42 DAT, respectively The higher carrier volumes controlled PA 88% 28 DAT and 42 DAT The use of air induction (AI) and flat fan (FF) nozzles did affect PA control though pe rcent coverage was different between these nozzles. These data agree with previous research that fomesafen applied with FF and AI nozzles did not affect percent control of Chenopodium album (common lambsquarters), Abutilon theophrasti (velvetleaf), and Ambrosia artemisiifolia (common ragweed) (Sikkema et al. 2008). However, as in this trial, it was o bserved that increased carrier volume resulted in increased contr ol (Sikkema et al. 2008). Although applications of lactofen were only 5 days apart, percent control of PA was affected by weed height and at time of application. Grichar (2007) has also dem onstrated that lactofen can control PA ( 92% ), when treated at the 5 to 10 cm height range. However, control decreased by 48% when the same herbicide was applied to PA at a higher height range of 15 to 20 cm. Also, lactofen was found to decrease percent c ontrol of PA with the increase of application time afte r crop planting (Mayo 1995).

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50 Research is limited on the effects of carrier volume and sprayer nozzle type with respect to individual weed efficacy The choice of nozzle type has become a critical d eci sion for crop producers. The s e data indicate that control of PA affected by noz zle type or carrier volume. However, with lactofen, control was significantly different when PA reached heights of 15 cm or greater. Acceptable control of PA, at 10 to 15 cm, with lactofen was achieved with carrier volumes of 187 and 281 L ha1. But PA was not sufficiently controlled when applied at a carrier volume of 94 L ha1. Thes e data suggest that weed size at time of application is most critical toward achieving optimum control. As weeds become larger, an incremental improvement in control can be achieved by increasing carrier volume to 187 L ha1.

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51 Figure 31. Influence of varying carrier volumes and nozzle type on percent spray coverage. Error bars calculated from the mean of 4 replications. AI = air induct ion nozzle, FF= flat fan nozzle.

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52 Table 3 1. Influence of carrier volume on % control of Palmer amaranth (height range of 5 cm to 10 cm) with the use of lactofen (0.21 kg/ha) + crop oil c oncentrate 1% (v/v). Carrier Volume ---------------------% control 1 ---------------------L/ha 14 DAT 2 28 DAT 42 DAT 94 L 99a 3 99a 99a 187 L 100a 99a 99a 281 L 100a 100a 100a 1 Visual assessment of Palmer amaranth control was based on the following scale: 0 = no control; 100 = complete control. 2 DAT = days after treatment. 3 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level acco rding to Fis hers Least Significant Difference (LSD) test.

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53 Table 3 2 Influence of carrier volume on % control of Palmer amaranth (height range of 15 cm to 2 0 cm) with the use of lactofen (0.21 kg/ha) + crop oil concentrate (1% v/v). Carrier Volume ---------------------% control 1 ---------------------L/ha 14 DAT 2 28 DAT 42 DAT 94 L 84b 3 82b 75b 187 L 91 a 8 9a 88 a 281 L 91a 89a 89a 1 Visual assessment of Palmer amaranth control was based on the following scale: 0 = no control; 100 = complete control. 2 DAT = days after treatment. 3 Values reflect the mean of 4 replications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fis hers Least Significant Difference (LSD) test.

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54 LIST OF REFERENCES Anonymous. 2005 Valor herbicide product label. Valent Publication No. 2005-VSX 0001. Walnut Creek, CA: Valent U.S.A. Corporation. 19 p. Anonymous. 2006. Ultra Blazer herbicide product label. United Phosphorus Publication No. 7050660(011608-2721). K ing of Prussia, PA: UPI. 6 p. Anonymous. 2007. Cobra herbicide product label. Valent Publication No. 2007-COB 0002. Walnut Creek, CA: Valent. 29 p. Anony mous. 2008. Prowl H2O herbicide product label. BASF Publication No. NVA 20 08041950353. Research T riangle Park, NC: BASF. 26 p. Anonymous. 2009 a Solicam herbicide product label. Syngenta Publication No. SCP 849A -L2E 1008 289881. Gr eensboro, NC: Syngenta. 50 p. Anonymous. 2009b Reflex herbicide product label. Syngenta Publication No. SCP 993A -L1G 1008. Gr eensboro, NC: Syngenta. 55 p. Anonymous. 2009c Reflex 24 (c) herbicide product label. Syngenta Publication No. AR0993028CA0209. G reensboro, NC: Syngenta. 2 p. Askew, S. D., J. W. Wilcut, and J. R. Cranmer. 1999. Weed management in peanut (Arachis hypogaea) with flumioxazin preemergence. Weed Technol. 13:594598. Barnes, J. P. and A. R. Putnani. 1986. Evidence of allelopathy by residues and aqueous extracts of rye (Secale cereale). W eed Sci. 34:384-390. Barnes, J. P., A. R. Putnam, and B. A. Burke. 1986. Allelopathic activity of rye (Secale cereale L.). In A. R. Putnam and C. S. Tang, eds. The Science of Allelopathy. John Wiley and Sons, Inc. New York, NY. P p 271286. Bond, J. A., L. R. Oliver, and D. O. Stephenson. 2006. Response of Palmer amaranth (Amaranthus palmeri ) accessions to glyphosate, fomesafen, and pyrithiobac. Weed Technol. 20:885892. Brown L., N. Soltani, C. Shropshire. H. Spieser, and P. H. Sikkema. 2007. Efficacy of four corn ( Zea mays L.) herbicides whe n applied with flat fan and air induction nozzles. Weed Biology and Management. 7:5561. Bryson, C. T. and M. S. DeFelice. 2009. Weeds of the South. Athens, GA: The University of Georgia Press. 34 p. Burgos, N. R. and R. E. Talbert. 1996. Weed control by s pring cover crops and imazethapyr in no -till southern peas ( Vigna unguiculata ). Weed Technol. 10:893899.

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55 Burke, I. C., M. S. Schroeder, W. E. Thomas, and J. W. Wilcut. 2007. Palmer amaranth interference and seed production in peanut. Weed Technol. 21:367-371. Dotray, P. A., T. A. Baughman, J. W. Keeling, W. J. Grichar, and R. G. Lemon. 2001. Effect of imazapic application timing on Texas peanut ( Arachis hypogaea). Weed Technol. 15:26 -29. Ehleringer, J. 1983. Ecophysiology of Amaranthus palmeri a sonoran desert summer annual. Oceologia. 57:107 112. Ellis, M.C.B, T. Swan, P.C.H. Miller, S. Waddelos, A. Bradley, and C. R. Tuck. 2002. Design factors affecting spray characteristics and drift performance of air induction nozzles. Biosyst. Eng. 82:289 296. Ether idge, R. E., A. R. Womac, and T. C. Mueller. 1999. Characterization of the spray droplet spectra and patterns of four venture type drift reduction nozzles. Weed Technol. 13:765770. Facelli, J. M. and S. T. Pickett. 1991. Plant litter: Its dynamics and eff ects on plant community structure. Bot. Rev. 57:2-32. Flanders, J T. and E. P. Prostko. 2003. Control of tropical spiderwort ( Commelina benghalensis ) in peanut with selected herbicides. Proc. American Peanut Res and Education Soc 35:47. Frans, R., R. Tal bert, D. Marx, and H. Crowley. 1986. Experimental design and techniques for measuring and analyzing plant responses to weed control practices. In N. D. Camper, ed. Research Methods in Weed Science. 3rd ed. Champaign, IL: Southern Weed Science Society. P p. 2946. Garvey, P. V. 1999. Goosegrass ( Eleusine indica ) and Palmer amaranth ( Amaranthus palmeri ) interference in plasticulture tomato. Ph.D dissertation. Raleigh, NC: North Carolina State University. 101 p. Gilbert, L. V., P. A. Dotray, E. P. Prostko, W. J. Grichar, J. A. Ferrell, and D. L. Jordan. 2009. Peanut re sponse to fomesafen. Proc. American Peanut Research and Education Soc. 41:12. Gleason, H. A. and A. Cronquist. 1991. Family Amaranthaceae, the Amaranth Family. In Manual of Vascular Plants of Nor theastern United States and Adjacent Canada. 2nd ed. New York: New York Botanical Garden. Pp. 104 108. Grey, T. L. and G. R. Wehtje. 2005. Residual herbicide control systems in peanut. Weed Technol. 19:560567. G richar, W J. 1992. Yellow nutsedge ( Cyperus esculentus ) control in peanuts ( Arachis hypogaea ). Weed Technol. 6:108-112.

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56 G richar, W. J., A. E. Colburn, and N. S. Kearney. 1994. Herbicides for reduced tillage production in peanut ( Arachis hypogeae) in the southwest. Weed Technol. 8:212216. Grichar, W. J. 1997. Control of Palmer amaranth ( Amaranthus palmeri ) in peanut (Arachis hypogaea)with postemergence herbicides. Weed Technol. 11:739 -743. Grichar, W. J. 2007. Horse purslane ( Trianthema portulacastrum ), smellmelon ( Cucumis melo ), and Palmer amaranth (Amaranthus palmeri ) control in peanut with postemergence herbicides. Weed Technol. 21:688-691. Grichar, W. J. 2008. Herbicide systems for control of horse purslane ( Trianthema protulacastrum L.), smellmellon ( Cucumis melo L.), and Palmer amaranth (Amaran thus palmeri S. Wats) in peanut. Peanut Sci. 35:3842. Heap, I. 2009. The international survey of herbicide resistant weeds. http://www.weedscience.org/In.asp. Accessed: January 10, 2009. Higgins, J. H., T. Whitwell, E. C. Murdock, and J. E. Toler. 1988. R ecovery of pitted morningglory ( Ipomoea lacunosa) and ivyleaf morningglory ( Ipomoea hederacea) following applications of acifluorfen, fomesafen, and lactofen. Weed Sci. 36:345353. Hoffman, M. L., E. E. Regneir, and J. Cardina. 1993. Weed and corn ( Zea may s ) responses to a hairy vetch ( Vicia villosa Roth) cover crop. Weed Technol. 7:594599. Horak, M. J. and T. M. Loughin. 2000. Growth analysis of four Amaranthus species. Weed Sci. 48:347 355. Hurst, H. R. 1992. Cotton lay by herbicides on wheat, vetch, and winter weeds as cover crops. Proc. Beltwide Cotton Conf. Memphis, TN. 3:13081312. Johnson, G. A., M. S. DeFelice, and Z. R. Helsel. 1993. Cover crop management and weed control in corn ( Zea mays ). Weed Technol. 7:425 430. Keeley, P. E., C. H. Carter, and R. J. Thullen. 1987. Influence of planting date on growth of Palmer amaranth ( Amaranthus palmeri ). Weed Sci. 35:199 204. Klingaman, T. E. and L. R. Oliver. 1994. Palmer amaranth ( Amaranthus palmeri ) interference in soybeans ( Glycine max ). Weed Sci. 42: 523 527. Knoche, M. 1994. Effect of droplet size and carrier volume on performance of foliageapplied herbicides. Crop Prot. 13:163178. Liebl, R., F. W. Simmons, L. M. Wax, and E. W. Stoller. 1992. Effect of rye (Secale cereale) mulch on weed control and soil moisture in soybean ( Glycine max ). Weed Technol. 6:838 -846.

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61 BIOGRAPHICAL SKETCH Michael is the son of Mike and Mitchell Dobrow. He was raised in a rural sugarcane and winter vegetable farming community in the glades area of Florida. Michael graduated high school in May 2001 and then attended Abraham Baldwin Agricultural College for two semesters He transferred to Santa Fe Community College where he graduated with an Associate of Arts degree in May 2005. Michael then attended the University of Florida receiving a Bachelor of Science degree in agronomy in May 2007. As an undergraduate student at the University of Flor ida, Michael was active in the Agronomy and Soils C lub and received the National Student Recognition Award presented by the Am erican Society of Agronomy, Crop Science Society of America and Soil Science Society of America. In the summer of 2007, Michael married the former Miss Casey Reynolds of Ocala, FL Michael started in the graduate weed science program at the University of Florida in the Fall of 2007. He started his field research in peanut weed control the summer of 2008. Michael has presented at the Southern Weed Science Society Florida Weed Science Society, and the Weed Science Society of America meetings. Following c ompletion of his Master of Science degree, he plans to continue, in some facet, his involvement in agriculture.