Citation
Weed Ecology and Management in Florida Potato (Solanum tuberosum L.) Production

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Title:
Weed Ecology and Management in Florida Potato (Solanum tuberosum L.) Production
Creator:
Rouse, Christopher E
Place of Publication:
[Gainesville, Fla.]
Florida
Publisher:
University of Florida
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english
Physical Description:
1 online resource (60 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Horticultural Sciences
Committee Chair:
DITTMAR,PETER J
Committee Co-Chair:
ZOTARELLI,LINCOLN
Committee Members:
MACDONALD,GREGORY E
Graduation Date:
12/13/2013

Subjects

Subjects / Keywords:
Agricultural seasons ( jstor )
Crops ( jstor )
Furrow irrigation ( jstor )
Furrows ( jstor )
Herbicides ( jstor )
Irrigation ( jstor )
Population density ( jstor )
Species ( jstor )
Tubers ( jstor )
Weeds ( jstor )
Horticultural Sciences -- Dissertations, Academic -- UF
control -- distribution -- enumeration -- herbicide -- movement -- seedbank -- weeds
Genre:
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Horticultural Sciences thesis, M.S.

Notes

Abstract:
Two studies were conducted for the purpose of this thesis:the first investigated the movement of weeds in seepage irrigated potato fields and the second developed new herbicide programs for weed control in potato.  Sub- surface seepage irrigation is the primary means by which potato is irrigated in Florida. In 2012 and 2013,a study was conducted to quantify weed population distribution and movement from the irrigation furrows and the start of the crop row, into potato crop fields. In-field weed counts and greenhouse weed seedbank enumeration were used to quantify weed populations and seedbank densities of four commercial potato fields in Flagler County, FL. In- field weed populations were significantly higher at the irrigation furrow and first tier (beginning of the crop row) as compared to the crop rows and all other tiers. Seedbank densities had significantly more weeds than the in-field population counts and the pattern of distribution were more variable. A higher density of weed seeds was often located in the crop rows, not the field edges. In-field weed counts were similar to observations by producers and researchers.  However, in-field counts did not predict the weed seed distribution within the fields. Adjusting seedbank enumeration to include only agronomicaly important weeds resulted in a more accurate representation of in field weed populations.  Experiments to evaluate potato tolerance and weed control of new season- long herbicide programs were conducted in 2012 and 2013 in Flagler County, Florida. Both experiments included fomesafen PRE,S-metolachlor PRE, and imazosulfuron POST; these three herbicides were applied alone and combined at varying rates for fourteen herbicide treatments. A grower standard (metribuzin + pendimethalin) and a nontreated control were also included. Potato crop tolerance trials were completed at the Florida Partnership for Water, Agriculture, and Community Sustainability at Hastings.Potato injury did not exceed 5% in either year and no effects on grade distribution or total yield were observed from any of the herbicides. Weed control studies were conducted at two on-farm locations. Differences in the weed species between years resulted in differences in weed control. In 2012, fomesafen f.b. imazosulfuron or S-metolachlor f.b. imazosulfuron had greater control of all species as compared to the nontreated control and the grower standard.  The POST application of imazosulfuron prolonged control following the PRE herbicides resulting in sustained weed control throughout the season.  In 2013, fomesafen and S-metolachlor provided similar control of the large crabgrass,however, no additional control from imazosulfuron. An herbicide program, which includes S-metolachlor or fomesafen PRE, and imazosulfuron POST is important for season long control of susceptible weeds with excellent potato tolerance. ( en )
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.
Thesis:
Thesis (M.S.)--University of Florida, 2013.
Local:
Adviser: DITTMAR,PETER J.
Local:
Co-adviser: ZOTARELLI,LINCOLN.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-12-31
Statement of Responsibility:
by Christopher E Rouse.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Embargo Date:
12/31/2014
Classification:
LD1780 2013 ( lcc )

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1 WEED ECOLOGY AND MANAGEMENT IN FLORIDA POTATO ( Solanum tuberosum L.) PRODUCTION By CHRISTOPHER EDWARD ROUSE 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 2013

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2 2013 Christopher Edward Rouse

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3 To my grandfathers

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4 ACKNOWLEDGMENTS My m of those people who have supported me throughout the process. I would like to thank my advisor Dr. Peter Dittmar for his encouragement, guidance, and the challenges he placed before me throughout my program. I also thank my committee members Dr. Lincoln Zotarelli and Dr. Greg MacDonald for their support and knowledg e throughout all of my research. I greatly appreciate the guidance and help I have been given from all of the Weed Scien ce faculty, staff, and students. My biggest thanks go to my parents, family and friends for supporting me and pushing me to keep moving forward to accomplish all of my goals. I thank Michelle Fehr for putting up with my stress and always being there for me no matter how difficult I became. Without the encouragement and assistance from Dr. Joshua Adkins, Charles Barrett, Christian Christensen and Clint Hunnicutt I would not have found the direction I wanted to go with my career nor be in the position I a m in today. I also want to thank Steve Greer and Robby Cox, two people who got me started and passionate about agriculture; without their mentoring I would have never started down this path and got to where I am today. Finally, this thesis is dedicated to my grandfathers: Charles Neverovich, Delano hree men who placed family and country above all else and have done everything possible to get me to where I am today. Even if they a re not with me I know all three of them supp ort me and will continue to support me in my future endeavors.

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5 TABLE OF CONTENTS p age ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF ABBREVIATION S ................................ ................................ ............................. 8 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 11 2 LITERATURE REVIEW ................................ ................................ .......................... 13 Potato Production ................................ ................................ ................................ ... 13 Sub surface Seepage Irrigation ................................ ................................ .............. 15 Weed Seedbank and Movement ................................ ................................ ............. 15 Studying Weed Seedbanks ................................ ................................ ..................... 17 Herbicides Use in Potato ................................ ................................ ........................ 18 Herbicides of Interest ................................ ................................ .............................. 19 Fomesafen ................................ ................................ ................................ ....... 19 Imazosulfuron ................................ ................................ ................................ ... 20 S metolachlor ................................ ................................ ................................ ... 21 Alternative Weed Management in Potato ................................ ......................... 2 2 3 EFFECT OF WEEDS IN SEEPAGE IRRIGATION FURROWS ON WEED SEEDBANK IN POTATO ( Solanum tuberosum L .) ................................ ................. 23 Background ................................ ................................ ................................ ............. 23 Materials and Methods ................................ ................................ ............................ 25 In Field Weed Counts ................................ ................................ ....................... 26 Seedbank Enumeration ................................ ................................ .................... 26 Data ana lysis ................................ ................................ ................................ .... 27 Results and Discussion ................................ ................................ ........................... 28 In Field Weed Counts ................................ ................................ ....................... 28 Seedbank Enumeration Weed Densities ................................ .......................... 29 4 SEASON LONG WEED CONTROL HERBICIDE PROGRAMS FOR FLORIDA POTATO PRODUCTION ................................ ................................ ........................ 41 Background ................................ ................................ ................................ ............. 41 Material s and Methods ................................ ................................ ............................ 43 Tolerance Study ................................ ................................ ............................... 44 Control Study ................................ ................................ ................................ .... 45

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6 Data analysis. ................................ ................................ ................................ ... 46 Results and Discussion ................................ ................................ ........................... 46 Tolerance Study ................................ ................................ ............................... 46 Control Study ................................ ................................ ................................ .... 47 5 CONCLUSION ................................ ................................ ................................ ........ 53 LIST OF REFERENCES ................................ ................................ ............................... 55 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 60

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7 LIST OF TABLES Table page 3 1 The 5 most common weed species using in field counts and seedbank enumeration in 4 potato ( Solanum tuberosum L.) fields in Hastings, FL. ........... 34 3 2 Effect of irrigation furrow and crop row on total number of weeds an d weed species in a 30 cm x 30 cm quadrat using in field counts. ................................ .. 35 3 3 Effect of fields edge and distance (tier) on total number of weeds and weed species in a 30 cm x 30 cm quadrat using in field counts. ................................ 36 3 4 Effect of irrigation furrow and crop row on to tal seedbank weed density from a 1,869 cm 3 soil core. ................................ ................................ ......................... 37 3 5 (tiers) on seedbank weed density from a 1,869 cm 3 soil core. ................................ ................................ ............................ 38 3 6 Effect of irrigation furrow and crop row on the adjusted weed seedbank density and adjusted species density. ................................ ................................ 39 3 7 density and adjusted species density. ................................ ................................ 40 4 1 Effect of s metolachlor and fomesafen followed by imazosulfuron on potato yield and tuber growth disorders in 2012 and 2013. ................................ ........... 50 4 2 Effect of fomesafen and s metolachlor followed by imazosulfuron in potato on weed control evaluation (%) for 2012 cropping season. ................................ ..... 51 4 3 Effect of s metolachlor and fomesafen followed by imazosulfuron in potato on large crabgrass control evaluation (%) for 2013 cropping season. ..................... 52

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8 LIST OF ABBREVIATIONS cm centimeter COC crop oil concentrate DAT days after treatment m meter MSO methylated seed oil NIS nonionic surfactant POST postemergence PRE preemergence v/v volume for volume WAT weeks after treatment

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9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of M aster of Science WEED ECOLOGY AND MANAGEMENT IN FLORIDA POTATO ( Solanum tuberosum L.) PRODUCTION By Christopher Edward Rouse December 2013 Chair: Peter J. Dittmar Major: Horticultural Sciences Two studies were conducted for the purpose of this thesis: the first investigat ed the movement of weeds in seepage irrigated potato fields and the second developed new herbicide programs for weed control in potato. Sub surface seepage irrigation is the primary means by which potato is irrigated in Florida. In 2012 and 2013 a study was conducted to quantify weed population distribution and movement from the irrigation furrows and the start of the crop row, into potato crop fields I n field weed counts and greenhouse weed seedbank enumeration were used to quantify weed populations an d seedbank densities of four commercial potato fields in Flagler County, FL In field weed populations were significantly higher at the irrigation furrow and first tier (beginning of the crop row) as compared to the crop rows and all other tiers. Seedbank densities had significantly more weeds tha n the in field population counts and the pattern of distribution w ere more variable. A higher density of weed seeds was often located in the crop rows, not the field ed ges In field weed counts were similar to obs ervations by producers and researchers. H owever, in field counts did not predict the weed seed distribution within the fields. Adjusting seedbank enumeration to include only

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10 agronomicaly important weeds resulted in a more accurate representation of in fi eld weed populations. E xperiments to evaluate potato tolerance and weed control of new season long herbicide programs were conducted in 2012 and 2013 in Flagler County, Florida. Both experiments included fomesafen PRE, S metolachlor PRE, and imazosulfuron POST; these three herbicides were applied alone and combined at varying rates for f ourteen herbicide treatments A grower standard (metribuzin + pendimethalin) and a nontreated c ontrol were also included Potato crop tolerance trials were completed at the Florida Partnership for Water, Agriculture, and Community Sustainability at Hastings. Potato injury did not exceed 5% in either year and no effects on grade distribution or total yield were observed from any of the herbicide s W eed control studies were conducted at two on farm locations. Differences in the weed species between years resulted in differences in weed control. In 2012, fomesafen f.b. imazosulfuron or S metolachlor f.b imazosulfu r on had greater control of all species as compared to the nontreated control and the grower standard. The POST application of imazosulfuron prolonged control following the PRE herbicides resulting in sustained weed control throughout the seaso n. In 2013, fomesafen and S metolachlor provided similar control of the large crabgrass however, no add itional control from imazosulfuron An herbicide program, which includes S metolachlor or fomesafen PRE, and imazosulfuron POST is important for season long control of susceptible weeds with excellent potato tolerance.

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11 CHAPTER 1 INTRODUCTION P otato production in Florida is located mainly in the Tri County Agricultural Area (St. Johns, Putnam, and Flagler Counties). The TCAA has a naturally high water table and impermeable soil layer resulting in sub surface seepage irrigation being the primary method to deliver water to the crops. Sub surface seepage irrigation, or simply seepage irrigatio n, uses long irrigation furrows, which are the length of the field to elevate the water table to the crop root zone, and is fairly unique to the state of Florida. These open, moist, and nutritionally rich irrigation furrows provide a habitat that has been observed to susta in large weed populations. Weeds that go unmanaged in agronomic fields can develop and disseminate seed or other propagules, contributing to weed competition and subseq uent yield losses during a cropping season. Little research has been conducted to evaluate the effect of irrigation furrows on the weed ecology and distribution patterns within the crop rows. The first section of research presented in this thesis seeks to understand more about the weed population distributions within the seepage irrigated potato fields. Results from this experiment help to provide more information on the distribution of weeds from unmanaged irrigation furrows and their effect on both in fi eld weed populations during the cropping season and the weed seedbank of these fields. Herbicides are the primary method of weed control in conventionally grown potato Season long herbicide programs use a combination of preemergence and postemergence he rbicides to prevent weeds from competing early in crop growth and control weeds, which often cause interference late r in the season. More recently developed h erbicides with broader weed control spectrums have been made available

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12 with the potential to great ly benefit potato producers. Most of these herbicides have not been evaluated for use in this system or in a weed control program designed to manage weed populations throughout the entire cropping season. The second section of this thesis focuses on evalua ting weed control efficacy and crop tolerance to herbicide based programs incorporating new active ingredients This research will provide potato growers with more effective herbicide based weed control programs throughout the cropping season and new metho ds to manage different weed species within their fields.

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13 CHAPTER 2 LITERATURE REVIEW Potato Production Cultivated potato ( Solanum tuberosum L. ), as it is known today, is a perennial of the Solanaceae family (Brosnan 2011). This family consists of other cultivated species including tomato ( S lycopersicum L. ) pepper ( Capsicum annuum L. ), and eggplant ( S. meolongema ) as well as weedy species such as jimsonweed ( Datura stramonium ) and black nightshade ( S. nigrum ) (Ency clopedia Brita n nica 2012). Members of the family are found in tropical regions of Latin America and less common in temperate areas with about 50 species located in the United States and Canada combined. Indigenous people of the Andes region first cultiva ted potato for its hardiness, ability to grow in poor soil, survive frosts, and produce high yields (Brosnan 2011) Early colonists of the Americas in the 16 th century used the potato throughout the coastal areas and it quickly became a part of the subsist ence diet of the region. The p otatoes adaptability along with its versatility has made it important in diets throughout the world Potato i s the 5 th most produced commodity in the world by tonnes, and the number one produced vegetable crop in 2010 (FAOSTA T 2012). Potato is a major vegetable crop in production weight, with 15 percent of the sales receipts for vegetables in the United States (ERS USDA 2012). The country produced about 18.3 million tons of potato, ranking 5 th in world production in 2010 (F AOSTAT 2012). Growing areas in the United States are primarily in the Pacific Northwest, with Idaho and Washington leading in production (ERS USDA 2012). Idaho is the number one producer with 30% of the U.S. production acreage at about 344 ,000 acre s of p otatoes in 2012 (USDA NASS 2013). About 90% of the U.S. potatoes are

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14 planted in the spring and harvested in the fall ; however some areas plant in the winter and harvest in the spring, as is done in Florida (ERS USDA 2012, Pack et al. 2003). Florida ranks 1 2 th nationall y, in production, with about 4.04 million metric tons produced in 2012; ranking second only to California for s pring production (USDA NASS 2013 ). Potato is grown throughout Florida with the primary growing region in the Hastings or Tri County Agricultural A rea (St. Johns, Flagler, and Putnam County). The Tri County area accounted for 64 % of potat o production in 2012 (USDA NASS 2013 ). Potato is divided into two consumption categories: fresh and processing (ERS USDA 2012) Florida grown potato is primarily grown for processing, mainly chipping, dictating how it is grown and marketed. T wo primary irrigation systems used in the state for potato production are overhead sprinkler and sub surface seepage irrigation (Dukes et al. 2010). Tillage is used to help with land preparation in order to properly form beds. After planting, potatoes are allowed to grow for a period of 2 3 week s and covered, in a process ensures the potato tubers are completely covered by the soil and not exposed to surface sunlight. Fertilization is typically applied pre plant with subsequent side dressed ap plication throughout the season, occurring boarding off (Zotarelli et al. 2012). A number of weeds im pact Florida potato growers including common ragweed ( Ambrosia artemisiifolia L.), amaranth species ( Amaranthus spp.), bermudagrass ( Cynodon dactylon L Pers.) and yellow nutsedge ( Cyperus esculentus L.) (Rouse et al. 2014 ). Weeds growing in direct competit ion with potato have the potential to impact potato tuber yield and quality (Hutchinson et al. 2011, Ciuberkis et al. 2007, Vangessell

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15 and Renner 1990). A population of mixed weed species which ar e able to compete for longer than 6 weeks without control, can significantly reduce tuber yield (Thakral et al. 1989). After this 6 week period any weeds that emerge are generally suppressed by the growth of the established potato. Full season weed competition, without any control, has the potential to reduce tub er yield by as much as 54% (Nelson and Thoreson 1981). Sub surface Seepage Irrigation Sub surface seepage irrigation, or simply seepage irrigation, accounts for 44% of the irrigated land in Florida (Dukes et al. 2010). Seepage irrigation is the primary so urce of potato field irrigation in the Hastings area Crops including tomato, sweet corn, and bell pepper also grown utilizing this system (Dukes et al. 2010). This system uses the flow of a high volume of water with gradually sloping fields to raise the w ater table to the crop root zone (Locascio 2005). Potatoes are grown in beds with 16 raised crop rows, one furrow on each side, with neighboring beds sharing a furrow. Due to the importance of field design, growers must grade the land with special equipme nt and skill to form the slope required for water movement. This system is inefficient and requires a lot of water, but growers prefer its low cost and ease of operation (Dukes et al. 2010). Weed Seedbank and Movement Weed species often occur in spatially aggregated or clumped areas within a production field (Marshall 1988). This aggregation can be due to soil factors, harvesting machinery, crop interactions, or herbicide efficacy (Rew and Cussans 1997). Within the w eeds develop viable propagules such as seeds, tubers, rhizomes, and vegetative pieces that have the potential to form or contribute to a weed seedbank within a field (Benvenuti 1995 Biniak and Aldrich 1986, Rahman et al. 2001, Sutton et al. 2006). It i s through weed seedbanks that weed populations often persist

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16 and serve as the primary source of weed infestations, ensuring future problems in weed management (Benvenuti 1995, Rahman et al. 2001). Persistence of seeds in the seedbank may be encouraged unde r different soils environments or other topographic features, which favor seed storage (Bagavathiannan et al. 2011). C ultivation and tillage, may place the seeds wi thin areas of the soil profile that encourage sustained viability within a system (Ball 1992). Weed movement is very prevalent within an agronomic system. Weeds move both vertically within the soil profile, and horizontally across the field, in response to abiotic and biotic factors withi n a system (Chambers and Macmahon 1994). Seed movement may occur by tillage equipment, manure, vehicles and wildlife Vertical movement of weed seed is movement within the soil profile. Weed seed germination and emergence occurs at a more shall depth in n o or minimal tillage practices compared to conventional tillage (Buhler and Mester 1991, du Croix Sisson 2000). Given a specific tillage system and sampling period, Avena fatua, Triticum aestivum, Polygonum convolvulus, Setaris viridis, and Echinochloa c rus galli have similar depths of emergence within 1.2 cm of each other (du Croix Sissons et al. 2000). Horizontal weed seed movement is across a field surface. Grundy et al. (1999) found the use of different implements, a rotovator or power harrow, resulte d in weed seed being distributed behind and beyond the point of impact. These primary tillage implements have the ability to increase certain annual weed species more rapidly within the seedbank (Ball and Miller 1990). Movement from hedgerow s into the fiel d was limited to the first 2.5 m of the field, only 30% of species in the hedgerow were found in the field (Marshal 1989). The impacts of field edges on other arable weed species and

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17 environments have shown similar results (Colbach et al. 2000). Rahman et al. (2001) noted seedbank densities declined along crop rows as a function of distance, of some weed species for some cases but not for all. Studying Weed Seedbanks Studying weed populations and seed densities within agricultural fields is often found to considered for evaluating weed populations: seedbank enumeration and aboveground in field weed counts. Cardina and Sparrow (1996) detail several seedbank enumeration methods includ ing growing weeds from soil samples, sieving and identifying seed from soil samples, and growing weeds from intact soil cores. These methods were found to be unreliable due to the propagule densities not properly describing the problematic weeds seen in th e fields. Alternative studies utilizing aboveground in field weed counts have been useful in identifying and characterizing weed populations. Broadleaf weed species within North Carolina soybean ( Glycine max ) uld be managed according to the densities of the weeds within a given area of the field (Wiles et al. 1992). The correlation of seedbank enumeration and in field counts may be species dependent. A direct correlation between seedbank and in field counts co uld be derived for Cardaria draba however, a similar correlation could not be drawn for Hordeum murinum (Makarian et al. 2007). Amaranthus deflexus can be correlated in no and conventional tillage (Isaac and Guimaraes 2007). Seedbank and above ground co unts could only be correlated in no till production systems due to limited movement

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18 Herbicides Use in Potato To reduce the impact of weed competition potato growers employ cultivation and herbicide applications to control weeds that are present within fields (Dittmar et al. 2012) A typical weed management program for potato in Florida is cultivation before planting, a pre emergen ce herbicide applicat emergence of the crop, mid emergent herbicide applications of herbicides (Stall and Sherman 1983). Applying herbicides with cultivation weed control programs will impact crop yield more then cultivation treatments alone, increasing weed control (Mulder and Doll 1993). Potato production systems currently are limited in the availability of herbicides for application during the cropping season (Bailey et al. 2002). More he rbicides are availabl e for pre emergence control tha n post emergence in Florida potato (Zotarelli et al. 2012) Improper application timing or unfavorable environmental conditions can result in crop injury to potato and must be monitored to prevent yield loss. Sulfentrazone applications in potato have reduced populations of common lambsquarter s ( Chenopodium album ) up to 98% when applied PRE at 110 to 280 g ha 1 (Bailey et al. 2002 ). However, late application of sulfentrazone at the time of potato emergenc e resulted in crop injury from 60 to 86% depend ing on rate. Sulfentrazone PRE, while low (58%), had similar control to metribuzin alone or metribuzin plus metolachlor. POST applications of rimsulfuron, metribuzin, and combinations of both, with combinatio ns of different adjuvants were found to cause early season injury in potato (Hutchinson et al. 2004). Injury was characterized by reduced height, leaf malformation, and some chlorosis Injury was greatest 2 weeks after treatment (WAT) but reduced to

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19 less t han 5% by row closure. The use of adjuvants also caused injury; with methylated seed oil (MSO) and crop oil concentrate (COC) injuring the crop more than a non ionic surfactant. Tuber yield and quality was not affected by the early season injury. Enviro nmental conditions can influence potato injury with different herbicide applications. Metribuzin alone under cloudy, cool, or wet conditions may result in potato injury (Hutchinson 2002). Hutchinson et al. ( 2004) found greater injury occurred when metribuzin was applied with either MSO or COC on a cloudy day Tonks et al. (2000) discussed the cool cloudy weather may have reduced potato tolerance to ethalfluralin and that further research should be conducted to det ermine the environmental effects on potato tolerance. Herbicides of Interest Fomesafen Fomesafen [ 5 [2 chloro 4 (trifluoromethyl)phenoxy] N (methylsulfonyl) 2 nitro benzamide] is a member of the di phenylether chemical family. Diphenylethers inhibit the en zyme protoporphyrinogen oxidase and are commonly referred to as PPO Inhibitors (Senseman 2007). Fomesafen is registered in cotton, dry beans, potatoes, snap beans and soybeans to control a range of weeds (Anonymous 2012). Fomesafen i s primarily applied pr e emergence with limited POST activity, and used to control broadleaf weeds with some yellow nutsedge control. POST application of fomesafen with a nonionic surfactant was able to increase control of common ragweed and hairy nightshade when applied at mul tiple growth stages of dry and edible pod beans (Bellinder et al. 2003). Multiple accessions of Palmer amaranth ( Amaranthus palmeri ) were controlled at least 96% with fomesa fen POST at 420 g ai ha 1 (Bond et al. 2006). Studies have indicated

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20 good to excellent control of broadleaf weeds and complete control of Powe l l amaranth ( Amaranthus powellii) and common purslane ( Portulaca oleraceae ) in cucumber ( Cucumis sativus ) (Peachey et al. 2012). Greater then 90% control of redroot pigweed ( Amaranthus retrof lexu s ), kochia ( Kochia scoparia (L.) Roth), and common purslane was observed with fomesafen application at 210 g ha 1 in dry beans (Wilson 2005). Sulfentrazone, another PPO inhibitor, tolerance of potato and weed species is due to differential root absorpt ion and uptake which may be similar to that of fomesafen (Bailey et al. 2003). Imazosulfuron Imazosulfuron [2 chloro N [[(4,6 dimethoxy 2 pyrimidinyl) amino] carbonyl]imidazo[1,2 a ]pyridine 3 sulfonamide] is a member of the sulfonylurea herbicide family of chemicals (Sensemen 2007). These are more commonly known as ALS inhibiting herbicides This group of herbicides inhibit acetolactate synthase, ceasing production of branched chain amino acid s (Sensemen 2007). Imazosulfuron is registered in other solan aceous crops including tomato and pepper (Felix and Boydston, 2010). It can be applied as both a PRE and POST herbicide, and has activity on a number of broadleaf species and yellow nutsedge with suppression of purple nutsedge ( Cyperus rotundus L. ) (Anonym ous 2011). R otational restrictions are required for leafy vegetables, cucurbits, and grain crops. Yellow nutsedge control with imazosulfuron in potato was found to be greatest with sequential applications, PRE followed by POST (450 g ai ha ` ) with 90 to 1 00% control (Felix and Boydston 2010). This same study showed 100% control of common lambsquarters and Am a ranthus ssp regardless of application timing. Injury was observed 14 days after treatment (DAT) at one location in the study, however the potato gre w out of the injury

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21 and it did not affect the yield. Greater weed control was observed when rainfall occurred within 10 days following PRE application of imazosulfuron, 70 mm in year one compared to 15 mm in year two (Riar and Norsworthy 2011). Application timing for specific weed species will have an effect on imazosulfuron efficacy. In bermudagrass turf, purple nutsedge control is greatest (91%) with sequential applications of imazosulfuron 3 weeks after initial application (Henry et al. 2012). Late POST applications made in drill seeded rice (Oryza sativa ) was not effective at controlling texasweed ( Caperonia palustris L.) four to five leaf stage, or hemp sesbania ( Sesbania herbacea) ; an early POST (texasweed at two to three leaf stage) application had greater then 82% control of both species (Godora et al. 2012). S metolachlor S metolachlor [2 chloro N (2 ethyl 6 methylphenyl) N (2 methoxy 1 methylethyl)acetamide] is a member of the chloroacetamide family. S metolachlor works by inhibiting the biosynthesis of fatty acids, lipids, proteins, isoprenoids and flavonoids (Sensemen 2007). Collectively, the family is known as seedling or shoot inhibitors It typically acts by inhibiting young developing shoots under the soil. S metolachlor is registered for use in a number of agronomic crops, pod crops, and potato (Anonymous 2009). S metol achlor can be applied as a PRE for control of annual grasses, some broadleaves, and yellow nutsedge control. Studies evaluating the efficacy of S metolachlor PRE found significant reductions of yellow nutsedge tuber production when halosulfuron plus dicamba is applied post in corn systems (Felix and Newberry 2012). Potato yield has been significantly reduced when sulfentrazone plu s metolachlor, the less active isomer of S metolachor, are applied at potato emergence (Bailey et al. 2002).

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22 Alternative Weed Management in Potato Boydston and Vaughn (2002) evaluated five weed management systems in central Washington potato production to reduce herbicide inputs through different cultivation and cover crop usage. A fall cover crop of rye, with banded metribuzin application, and reservoir tillage helped to reduce PRE herbicide inputs by 66%, with tuber yields equivalent to that of standard herbicide treated plots. However, the use of rapeseed with cover crop and in season reservoir tillage decreased tuber yield up to 30%. Using information from weed seedbank and current aboveground in field weed populations, researchers and producers may be able to better predict seed movement and associated interference. This could allow for more appropriate integrated management measures to be taken.

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CHAPTER 3 EFFECT OF WEEDS IN SEEPAGE IRRIGATION FURROWS ON WEED SEEDBANK IN POTATO ( Solanum tuberosum L .) Background Florida produced over 400 thousand metric tons of potato in 2012 ranking 12 th overall in US production (USDA NASS 2013). Fourteen thousand hectares were harvested in 2012 from across the state with 64% grown in the Hastings or Tri County Agricultural Area (TCAA) (USDA NASS 2013). The TCAA is in the northeastern part of the state and consists of St. Johns, Putnam, and Flagler counties. The primary form of irrigation in the region is subsurface seepage irrigation. Subsurface seep age irrigation or seepage irrigation is used on 44% of the irrigated acreage in Florida (Dukes et al. 2010). This method is used in combination with other types of irrigation or alone in tomato ( Solanum lycopersicum L. ), pepper ( Capsicum annuum L. ), strawb erry ( Fragaria ananassa ), cabbage ( Brassica oleracea ) corn ( Zea mays) and other crops grown throughout the state This system uses the flow of a high volume of water with gradually sloping fields to raise the water table to the crop root zone (Locascio 2 005). The crops are grown in beds with an irrigation furrow on both sides and a single irrigation furrow joining neighboring beds. The water moving through the soil profile encounters a hardpan, forcing the water to spread across the bed and through capill ary action increases the water table. Overall, the design of the system is inefficient and requires large quantities of water, however, growers prefer the low cost and ease of operation (Dukes et al. 2010). Seepage irrigation furrows receive minimal to no weed management. The impact of these furrows on crop weed management and dyn amics has not been investigated. H owever by

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24 researchers in other cropping systems (Rahman et al. 2001, Benve nuti 2007, Devlaeminck et al. 2005 ). Weeds may move horizontally or vertically by a number of abiotic and biotic factors if given the means to do so and tend to be spatially aggregated or clumped within a production field ( Chambers and Macmahon 1994; Marsh all 1988). This aggregation can be due to soil environments harvesting machinery, crop interactions, or herbicide efficacy (Rew and Cussans 1997). Weeds that develop viable propagules such as seeds, tubers, rhizomes, and vegetative pieces have the potent ial to develop or contribute to a weed seedbank within a field (Benvenuti 1995). W eed seedbanks serve as the primary source of weed infestations, ensuring future problems in weed management (Benvenuti 1995, Rahman et al. 2001). The same factors which contr ibute to weed aggregation and dissemination, such as cultivation and tillage, may place the seeds within areas of the soil profile, which encourage sustained viability within a system (Ball 1992). Studying weed populations and seed densities within agricu ltural fields is often found considered for evaluating weed populations: seedbank enumeration and aboveground in field weed counts. Cardina and Sparrow (1996) detail several see dbank enumeration methods including growing soil samples, sieving and identifying seed from soil samples, and growing weeds from intact soil cores. These methods were found to be unreliable due to the propagule densities not properly describing the problem s seen in the fields. Rahman et al. (2001) noted seedbank densities indicated a decline along crop rows due to clumping of the seeds together from either large plant source or a small group of plants aggregating together

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25 Alternative studies utilizing abo veground in field weed counts have been useful in identifying and characterizing weed populations. Broadleaf weed species within North Carolina soybean fields ( Glycine max managed according to the densities of the weeds within a given area of the field (Wiles et al. 1992). Using information from the seedbank and current aboveground in field weed populations, researchers and producers may be able to better predict seed movement and associated interference. This could allow for more appropriate integrated management measures to be taken. Seepage irrigation results in cultural and pest management practices that are different than most other agronomic and horticultural crops. Irrigation furrows within crop fields pr ovide a constant source of weed propagules, while w eeds within the crop rows and field edges also have the potential to contribute to the seedbanks. An improved understanding of factors that affect the ability of a seed to persist in this environment may h elp reduce weed populations year after year (Taylor and Oliver 1997). The objective of this study is to quantify the distribution of weed populations and movement in seepage irrigated fields from the irrigation furrows and start of the rows into potato cr op row s Materials and Methods Four fields currently in potato production using seepage irrigation within the Hastings area of Florida were sampled for weed populations and seedbank densities in 2012. Fields were selected based on weed populations that were considered typical for seepage irrigated systems. Three crop beds (3 replications) located next to each other within the center portion of each field were included for the experiment. A bed contained 16 crop rows and an irrigation furrow on either sid e of the bed. Beds were grid sampled

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26 (equidistantly spaced) for a total of sixty three sampling sites within a replication. Sampling sites began at the irrigation furrow then 8 subsequent crop rows across the bed with 1.1 m intervals for 9.12 m for a total of 9 sampling sites. Sampling sites along the irrigation furrow and crop rows were sampled at 15.2 m intervals for 91.4 m, for a total of 7 sampling sites along the crop row Weed densities at each of the sampling sites were determined using in field weed counts and seedbank analysis. In F ield W eed C ounts In field populations were counted one time in the spring of 2012 early in the potato crop season prior to canopy closure A 30 x 30 cm quadra t was placed at each sampling site and w eeds were identified, by species, counted, and recorded for further analysis. Seedbank E numeration S oil samples were collected from each sampling sites using a sampling tool with a diameter of 11.5 cm and a length of 18 cm for a total volume of 1,869 cm 3 Upon removal from the field, the soil was placed into a plastic bag, labeled and refrigerated at 4.4 C. Samples were kept in refrigeration for storage and cold stratification of the weed seeds After a period of 5 weeks, samples were removed from cold s torage and seeds were allowed to germinate under greenhouse conditions at the Plant Science Research and Education Center in Citra, FL. Individual samples were evenly distributed into three individual cells of a six cell plastic tray to a volume of 623 cm 3 per cell Samples were irrigated using automatic overhead irrigation with two 180 second irrigation events during the day to maintain soil moisture Enumeration began three weeks after placement in the greenhouse, and bi weekly there after for 10 weeks i n the summer and fall of 2012. E merged weeds were identified by species counted, and removed from

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27 the cells Following the first season of enumeration in 2012, soil samples were removed from the tr ays and placed in plastic bags and moved back into the re frigerated storage until the following year. In 2013 samples were returned to the greenhouse using the same method as previously described for 11 wk Two enumeration periods were used to ensure emergence of warm and cool season weeds. Data A nalysis In field weed populations and seedbank density were analyzed with a general field weed populations and greenhouse seedbank densities were analyzed separately. Weed densities were grouped according the row and corresponding tier, which are defined as sampling sites along the furrow and crop rows, were combined for row weed count and species means. Rows are identified as the irrigation furrow and potato rows 1 through 8. Tiers a re the mean of the irrigation furrow and crop rows at each of the field counts, total weed population is the cumulative number of weeds at a sampling site. For seedbank enumeratio n, seedbank weed density is the total number of weeds that grew from the soil core from each sampling site. For both in field weed counts and seedbank densiti es, the total number of species for each sampling site was analyzed for all rows and tiers. Furth er analysis of the seedbank enumeration data included an based on the presence of a species in the field. For example, if large crabgrass ( Digitaria sanguinalis (L.) Scop. ) was found in both the seedbank and the field studies, the weed densities for the seedbank were evaluated to determine if similar population trends were exhibited in the seedbank compared to the field.

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28 Results and Discussion Due to differences between locations for all variables, each location was analyzed independently. Weed populations, seedbank densities, and number of species were included for all sampling sites. Data were analyzed without the irrigation fur row and first tier to limit varian ce created by the high weed populations and to determine the significance of the weed populations and densities within the planted crop rows. The result of removing the first row or tier did not affect the mean separation among crop rows (data not shown). A list of the 5 most abundant weed species at each of the locations for in field weed populations and seedbank weed densities can be found in T able 3 1. The number of total species in the seedbank study was greater than the number of species for the in fie ld counts (Tables 3 4 through 3 7). In Field Weed Counts Row effect The irrigation furrow in all of the fields contained the highest total population of weeds as compared to all the crop rows (Table 3 2). Weed populations within the crop rows of fields B, C, and D, were not different. However, in field A, row 1 had a greater weed population than row 6; all of the other rows were similar to crop rows 1 and 6. Although this trend was also identified in f ield D, the furrow and crop rows had less than one weed. Irrigation furrow weed management and higher intensity cultural practices resulted in many evaluation sites within field D to have no weeds in either the furrow or crop rows. The greatest species div ersity was in the irrigation furrow, similar to that of the weed populations (Table 3 2). Crop rows in f ields A, B, and C were significantly different from each other but did not exceed 1.05 species In field A, rows 1 and 2 had more weed species than row s 7 & 8. In field C, row 1 had more weed species than rows 2

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29 through 8. Again, in field D all the crops rows were similar, however, the furrow and crop rows had less than 1 species. Tier effect. The total weed population was higher at the first tier, or start of the row compared to all other tiers in fields A and B (Table 3 3). Total weed populations within the tiers of the inner part of the field were statistically similar to each other. Field B and C did not have different weed populations among tiers. Species diversity was greatest at tier 1 for all fields; in fields B and C the tiers within the field were all similar. Seedbank Enumeration Weed D ensities Row effect. In field A total weed dens ities were significantly higher for the irrigation furrow and first row within the bed at greater than 199 weeds for all of the sampling sites (Table 3 4). Rows 2 through 8 were highly variable with no consistency in means indicating no pattern to the weed distributions. In field C, the highest density (>122) was found in the sixth and eighth rows, but this was not different from the other crop rows. T he irrigation furrow, with 97 weeds, had significantly less weeds than rows 6 and 8. Fields A, B, and C ha d the greatest species diversity within the irrigation furrow. Field D had a greater number of species in the first crop row however this was similar to the irrigation furrow and rows 3 through 6. Adjusted weed density is the exclusion of weed species not found in the in field weed counts. The adjusted weed density resulted in lower total weed populations w ithin all of the fields (Table 3 6 ). The highest density of weeds was located at the irrigation furrow (27 plants) with all the crop rows having lower densities The lowest weed density was at rows 7 and 8, the farthest distance from the irrigation furrow which was similar to all the crop rows. Adjusted w eed seed densities within Field B were not significant among the irrigation furrow and crop rows; the difference between the

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30 original and adjusted densities was not as great as the other fields under evaluation. The greatest weed density in Field B was 150 weeds and only reduced to 79 weeds; all of the other fields were reduced by at least 90% followin g the removal of the non agronomically relevant weed species. The similar species in field C and D had inverse trends of the original weed population. The highest adjusted weed density was in the furrow and lowest density in row 8. Row 8 was similar to rows 3 through 7 in field C and rows 2 through 7 in field D. The adjusted species density also resulted in the highest diversity within the irrigation furrow in fields B and C. However both the irrigation furrow and the first crop row had the greatest de nsity in fields A and D. Tier effect. In fields A and D, the greater total weed density was in tiers 2 to 6 followed by tier 1 (Table 3 5). The first tier had a greater total weed density than the other tiers in fields B and C. In field B, the lowest weed density was in tier 4 and was similar to tiers 3 and 5. The highest species diversity for Fields A and C was at the 4 th tier, or 46 m from the start of the row; the lowest diversity was in the first tier for Field A and the last tier for Field D. Field B a nd C had similar results to the total weed density, and the highest diversity was in the first tier. Field B had no differences among tiers for adjusted weed densities (Table 3 7). Field A had a greater density of weeds in the inner tiers 4 through 6. Af ter removing dissimilar species, the highest weed density in field A was tier 5, which was similar to tier 4 and 6. Field D was similar, with rows 2 through 5 having the greatest density, but was similar to tiers 1 and 6. Field C followed a similar patter n to the in field weed population with the highest density at the first tier and the subsequent tiers being less. The adjusted species diversity in field A was not significant amongst the differing tiers.

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31 Fields B and C did follow a similar trend to the in field weed populations with the highest diversity at the first tier. Field D had less of a pattern to the seedbank distribution with the inner tiers having a greater species diversity then the other tiers but still similar to all but the last tier. Total in field weed populations and species diversity were consist within all fields for both row and tier analysis, indicating that both the irrigation furrow and beginning of the crop rows have higher weed populations. Greater diversity of species was exhibi ted in areas that also had a larger population of weeds. The irrigation furrow, which contains higher concentrations of water, leached nutrients, and reduced potato crop competition, had a greater number of weeds and species. This soil environment is more suitable for sustaining problematic weeds tha n other areas with a competing crop or dryer conditions, such as the beginning of a crop row. Herbicide use may have resulted in reductions in the total species diversity within a crop row. Some herbicide may co ntrol a particular species but not all the weeds present within a sample site. Seedbank densities were highly variable and inconsistent among the different locations under evaluation, similar to other studies (Cardina and Sparrow 1996). Tiers in Field A a nd Field D and rows in Field C and Field D contained higher seed densities within the crop rows as compared to the more open and ideal environments in the irrigation furrow. Higher weed seed densities than in field weed populations were also noted, especi ally in Field D, where the crop rows in the field had populations of less than one weed but the seedbank densities exceeded 250 weeds. This is more than likely the result of herbicide use and an increased effort by the producer to reduce weeds with residu al herbicides that suppress the growth of weeds in the crop rows.

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32 through 7 in Field B were identified by having higher populations with little to no distribution around them, much like other studies (Wiles et al. 1992). These clumps were not, however, found in the field study because herbicide use and crop competition within the crop rows reduced weed emergence and resulted in significantly lower populations than the irrigation furrow. While there was no distinct pattern of weed seed distribution by tillage implement or other mechanized means, this equipment may have still caused the uneven distribution and aggregation (Cousens et al. 2006). Current grower practices for site preparation include harrowing the field starting at one irrigation furrow and moving along the crop rows, back and forth approximately 3 times, until they have reached the irrigation furrow on the other side of the bed. Following this initial tillage they then make tw o more passes at a 45 degree angle across the bed. This mixing and movement of soil, and subsequently weed seed, would contribute to the disaggregated nature of the seedbank. Adjusting weed seedbank densities which were variable, to the in field weed pop ulations, resulted in p atterns of weed distribution that were more characteristic of the observations being made about seepage irrigated fields This adjustment resulted in removal of a number of non agronomically relevant weed species including winged wa ter primrose or low falsepimpernel that are often controlled by herbicides or outcompeted by the potato. Most of these weeds originate from natural areas surrounding the fields or from areas deeper within the soil profile, which retained seed from the years preceding its agricultural use (Devlaeminck et al. 2004) Seedbanks without these non agronomic weeds or with species similar to the in field populations,

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33 such as field B, may not require this adjustment. Use of this comparison is a much better predicto r of in field weed populations from seedbank enumeration techniques. The results of this study provide insight into the weed distributions of seepage irrigated potato fields within this area of Florida. In field weed populations were consistent with wha t was being observed by both producers and researchers. Further examination into the weed seed distribution within the seedbank was less consistent. The seedbank is not the best predictor of in field populations or of the prevalent weed distribution. It d oes, however, provide insight into all the possible weed populations present in the field, which is important when developing off season management programs or in predicting the potential impact that reduced weed management may have. Seedbank densities onl y became of value following removal of the non agronomic species and using the species identified in the field during the growing season. This study does not provide for alternative management strategies or describe patterns of yield reduction in the field due to weed competition. Further studies looking at specific equipment use or management within this system need to be conducted to better understand their impacts on weed seed distribution within the fields. Crop competition, herbicide use, or unfavorabl e environmental conditions could have contributed to this difference in weed density within the field.

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Table 3 1. The 5 m ost common weed species using in field counts and seedbank enumeration in 4 potato ( Solanum tuberosum L.) fields in Hastings, FL. Field A Field B Field C Field D In field weed counts yellow nutsedge Cyperus esculentus Rumex sp. bermudagrass Cynodon dactylon common ragweed Ambrosia artemisiifolia common ragweed Ambrosia artemisiifolia yellow nutsedge Cyperus esculentus Amaranthus sp. Amaranthus sp. bermudagrass Cynodon dactylon common ragweed Ambrosia artemisiifolia Rumex sp. Rumex sp. entireleaf morningglory Ipomoea hederacea eclipta Eclipta prostrata Common cocklebur Xanthium strumarium Solanum sp. grain sorghum Sorghum bicolor Seedbank enumeration low falsepimpernell Lindernia dubia wandering cudweed Gnaphalium pensylvanicum annual sedge Cyperus compressus low falsepimpernell Lindernia dubia old world diamond flower Oldenlandia corymbosa oldfield toadflax Nuttallanthus canadensis winged waterprimrose Ludwigia decurrens winged waterprimrose Ludwigia decurrens Walt. crowfootgrass Dactyloctenium aegyptium Florida pimpernel Anagallis pumila low falsepimpernell Lindernia dubia old world diamond flower Oldenlandia corymbosa winged waterprimrose Ludwigia decurrens low falsepimpernell Lindernia dubia old world diamond flower Oldenlandia corymbosa green kyllinga Kyllinga brevifolia Cyperus sp. winged waterprimrose Ludwigia decurrens crowfootgrass Dactyloctenium aegyptium annual sedge Cyperus compressus a Weeds go in order from the most to lea s t abundant in descending order within the field.

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35 Table 3 2. Effect of irrigation furrow and crop row on total number of weeds and weed species in a 30 cm x 30 cm quadrat using in field counts. Weed population Total species Row Field A Field B Field C Field D Field A Field B Field C Field D Irrigation furrow 8.52 a a 14.95 a 7.29 a 0.14 a 1.90 a 2.10 a 1.67 a 0.14 a 1 1.81 b 2.57 b 1.19 b 0.00 b 0.67 b 0.86 bc 0.71 b 0.00 b 2 1.52 bc 2.57 b 0.86 b 0.00 b 0.52 bc 1.05 b 0.38 c 0.00 b 3 1.24 bc 1.76 b 0.86 b 0.05 b 0.38 bcd 0.76 bc 0.29 c 0.05 b 4 1.00 bc 1.52 b 1.24 b 0.05 b 0.29 cd 0.81 bc 0.24 c 0.05 b 5 1.11 bc 2.67 b 1.48 b 0.00 b 0.43 bcd 1.00 b 0.24 c 0.00 b 6 0.38 c 1.24 b 1.48 b 0.00 b 0.24 cd 0.76 bc 0.19 c 0.00 b 7 0.57 bc 0.91 b 1.29 b 0.00 b 0.19 d 0.43 c 0.24 c 0.00 b 8 0.62 bc 1.76 b 1.10 b 0.00 b 0.19 d 0.62 bc 0.19 c 0.00 b a Values with the same letter are statistically similar to each other

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36 Table 3 3. Effect of fields edge and distance (tier) on total number of weeds and weed species in a 30 cm x 30 cm quadrat using in field counts. Weed population Total species Tier Field A Field B Field C Field D Field A Field B Field C Field D 1 4.93 a a 3.07 a 6.93 a 0.07 a 1.04 a 1.41 a 1.41 a 0.07 a 2 0.85 b 2.11 a 1.19 b 0.00 a 0.44 bc 0.89 b 0.44 b 0.00 a 3 1.22 b 2.69 a 1.00 b 0.00 a 0.41 bc 0.85 b 0.30 b 0.00 a 4 1.15 b 3.37 a 0.81 b 0.07 a 0.30 c 0.85 b 0.19 b 0.07 a 5 1.56 b 2.74 a 1.52 b 0.04 a 0.44 bc 0.67 b 0.33 b 0.04 a 6 1.70 b 4.33 a 0.63 b 0.00 a 0.59 b 0.89 b 0.26 b 0.00 a 7 1.67 b 4.70 a 0.96 b 0.00 a 0.52 bc 0.96 b 0.30 b 0.00 a a Values with the same letter are statistically similar to each other

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37 Table 3 4. Effect of irrigation furrow and crop row on total seedbank weed density from a 1,869 cm 3 soil core Total weed density Total species density Row Field A Field B Field C Field D Field A Field B Field C Field D Irrigation furrow 203.67 a a 149.57 a 96.76 b 134.05 c 13.71 a 15.24 a 11.86 a 11.29 ab 1 199.14 a 109.33 c 115.76 ab 251.05 b 13.38 a 13.05 b 10.76 a 12.10 a 2 156.19 bc 109.38 c 107.71 ab 279.76 ab 10.05 b 12.19 bc 8.71 b 11.48 ab 3 117.90 cd 104.71 c 109.19 ab 307.14 ab 8.57 c 11.24 cd 7.86 bc 11.48 ab 4 165.05 b 115.14 c 116.67 ab 297.76 ab 10.14 b 10.95 cd 8.00 bc 11.71 ab 5 133.33 bcd 135.86 ab 114.81 ab 316.57 ab 9.24 bc 10.95 cd 7.52 bc 11.14 ab 6 158.67 b 120.86 bc 122.33 a 311.90 ab 9.33 bc 10.00 d 7.10 c 11.57 ab 7 139.33 bcd 125.62 bc 117.05 ab 329.14 a 8.43 c 10.52 d 7.90 bc 10.52 b 8 120.86 cd 114.48 c 123.62 a 335.90 a 8.76 bc 10.29 d 8.29 bc 10.52 b a Values with the same letter are statistically similar to each other

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38 Table 3 5. (tiers) on seedbank weed density from a 1,869 cm 3 soil core. Total weed density Total species density Distance Field A Field B Field C Field D Field A Field B Field C Field D 1 88.19 b a 144.15 a 152.07 a 203.22 b 9.19 c 13.44 a 11.11 a 10.81 bc 2 153.00 a 124.63 b 104.04 b 281.74 a 10.04 abc 12.22 ab 9.30 b 11.33 abc 3 152.85 a 116.44 bc 109.59 b 293.89 a 9.96 bc 11.74 bc 8.78 bc 11.89 ab 4 185.63 a 101.48 c 105.78 b 309.74 a 11.22 a 10.63 cd 7.89 cd 12.15 a 5 171.22 a 114.07 bc 103.33 b 307.00 a 10.19 abc 10.78 cd 8.19 bcd 11.22 abc 6 169.67 a 123.00 b 115.15 b 301.19 a 10.73 ab 11.97 bc 8.07 bcd 11.20 abc 7 163.04 a 120.07 b 106.41 b 296.89 a 9.83 bc 10.25 d 7.25 d 10.50 c a Values with the same letter are statistically similar to each other

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39 Table 3 6. Effect of irrigation furrow and crop row on the adjusted weed seedbank density and adjusted species density. Adjusted weed densities Adjusted species densities Row Field A Field B Field C Field D Field A Field B Field C Field D Irrigation furrow 26.95 a a 78.43 a 17.33 a 9.43 a 4.00 a 5.05 a 3.10 a 2.86 a 1 11.05 b 62.67 a 5.95 b 8.33 ab 3.38 a 3.57 b 1.67 b 2.76 a 2 4.29 c 65.19 a 2.24 c 7.05 ab 1.81 b 3.29 b 0.86 c 2.14 b 3 3.43 c 60.67 a 1.29 c 7.10 ab 0.86 c 2.95 b 0.62 c 2.33 ab 4 5.43 c 59.33 a 2.00 c 6.71 ab 1.76 b 3.05 b 0.86 c 1.95 b 5 3.86 c 79.33 a 1.14 c 7.10 ab 1.62 bc 3.00 b 0.57 c 2.00 b 6 4.00 c 69.10 a 0.71 c 7.33 ab 1.33 bc 2.86 b 0.43 c 2.05 b 7 2.71 c 73.81 a 1.43 c 5.67 ab 1.00 bc 3.10 b 0.57 c 1.76 b 8 3.10 c 61.67 a 2.10 c 5.14 b 1.98 bc 3.00 b 0.62 c 1.71 b a Values with the same letter are statistically similar to each other

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40 Table 3 7. (tiers) on the adjusted weed seedbank density and adjusted species density. Adjusted weed densities Adjusted species densities Distance Field A Field B Field C Field D Field A Field B Field C Field D 1 5.96 b a 69.82 a 5.52 a 6.63 ab 1.78 a 3.59 ab 1.63 a 2.07 ab 2 4.44 b 67.00 a 4.41 ab 7.96 a 1.70 a 3.44 abc 1.19 ab 2.19 ab 3 6.00 b 64.52 a 3.82 ab 9.07 a 1.67 a 2.85 c 1.11 b 2.59 a 4 8.89 ab 62.15 a 3.41 ab 8.11 a 2.30 a 3.00 bc 0.81 bc 2.33 a 5 11.89 a 72.41 a 4.19 ab 7.59 a 2.30 a 3.30 abc 0.85 bc 2.07 ab 6 7.93 ab 68.70 a 3.37 ab 6.26 ab 2.00 a 3.90 a 1.00 bc 2.20 ab 7 4.96 b 70.00 a 1.89 b 4.04 b 1.54 a 3.04 bc 0.58 c 1.71 b a Values with the same letter are statistically similar to each other

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41 CHAPTER 4 SEASON LONG WEED CONTROL HERBICIDE PROGRAMS FOR FLORIDA POTATO PRODUCTION Background Potato ( Solanum tuberosum L.) production is a valuable segment of Florida's agricultural production. Over 400,000 tons were produced in 2012, on over fourteen thousand hectares ; Florida ranks 12th nationally for production weight (USDA NASS 2013). Potato is grown in nearly all of the growing regions dis tributed throughout the state and a County Agricultural Area (TCAA)(USDA NASS 2013). T he TCAA is in the northeastern part of the state and consists of St. Johns, Putnam, and Flagler counties. Many crops are often used in rotation with potato including: cabbage ( Brassica oleracea L. var. capitata) corn ( Zea mays L.) cucurbits, and sorghum cover crop A number of weeds impact Florida potato growers including common ragweed ( Ambrosia artemisiifolia L.), pigweed species ( Amaranthus spp.), bermudagrass ( Cynodon dactylon L Pers.) and yellow nutsedge ( Cyperus esculentus L.) (Rouse et al. 2014 ). Weeds growing in direct competition with potato have the potential to impact potato tuber yield and quality (Hutchinson et al. 2011, Ciuberkis et al. 2007, Vangessell and Renner 1990). Weeds allowed to compete for longer th an 6 weeks without control, can significantly reduce tuber yield (Thakral et al. 1989). Following this 6 week period weeds that emerge are suppressed by the potato growth and will not impact total yield Full season weed competition without any control has the potential to reduce tuber yield by as much as 54% (Nelson and Thoreson 1981). To reduce the impact of weed competition potato growers employ cultivation and herbicide applications to control

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42 weeds that are present within fields (Dittmar et al. 2012). A typical weed management prog ram for potato in Florida is : cultivation before planting, a pre emergence herbicide and before re emergence of the crop, mid row emergence herbicide applications of herbicides the recently emerged potato plants are covered with soil to prevent tubers from being exposed to direct sunlight during development Potato production systems are limited in the a vailability of herbicides for application during the cropping season and m ore herbicides are labeled for pre emergence th a n post emergence control in Florida ( Bailey et al. 2002, Zotarelli et al. 2012). Fomesafen is a soil applied preemergence herbicid e with limited postemergence a ctivity and controls broadleaf weeds wi th some yellow nutsedge control; it was labeled for use in the state for potato in 2012 (Anonymous 2012). Residual control of Powell amaranth ( Amaranthus powellii S. Wats. ) and common purslane ( Portulaca oleraceae L. ) has been documented in cucumber (Peachey et al. 2012). Sicklepod ( Senna obtusifolia (L.) H.S. Irwin & Barneby ), Ipomoea species, and common cocklebur ( Xanthium strumarium L. ) control is not, however, increased with a fome safen application followed by glyphosate as compared to a glyphosate only application (Stephenson et al. 2004). S metolachlor is a soil applied PRE herbicide registered for use in a number of agronomic crops, pod crops, and potato for control of annual grasses, some broadleaves, and yellow nutsedge ( Anonymous 2009 ). S metolachlor significantly reduced yellow nutsedge tuber production when followed by halosulfuron and dicamba

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43 as compared to S metolach lor alone (Felix and Newberry, 2012). S ulfentrazone + metolachlor the less active isomer of S metolachlor, applied at emergence reduced total potato yield and redistributed the potato tuber grades resulting in a decrease of lower grade tubers and an incre ase of extra large ones (Bailey et al. 2002). Application of S metolachlor and fomesafen co applied as a preemergence treatment can has the potential to increase weed control in cucurbits from 69% to 95% (Peachey et al. 2012). Imazosulfuron can be applied both PRE and POST with activity on a number of broadleaf species and yellow nutsedge and suppression of purple nutsedge ( Cyperus rotundus L.) (Anonymous 2011). Purple nutsedge control increase d (91%) when imazosulfuron at 0.56 kg ha 1 is applied every 3 weeks with sequential applications (Henry et al. 2012). Imazosulfuron at 450 to 560 g ha 1 provides similar control of yellow nutsedge and broadleaf weeds to current herbicides used in potato production ; however proper irrigation foll owing application is required for adequate yellow nutsedge con trol (Felix and Boydston 2010). Rainfall occurring within 10 days of application increase d (Riar and Norsworthy 2011). With so few herbicides avail able and limited control program s established for use in potato; new season long herbicide based control programs need to be evaluated for use in the unique soils, environment, and weed spectrum in Florida potato. The objective of this study is to evaluate the effi cacy and tolerance of PRE and POST herbicides for use in a season long herbicide program for Florida potato producers. Materials and Methods Separate studies were conducted to evaluate crop tolerance and weed control efficacy of PRE and POST herbicide treatments in potato i n the spring of 2012 and 2013.

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44 Tolerance Study Studies were completed at the Florida Partnership for Water, Agriculture, and Community Sustainability Research Station in Hastings, FL on a Ellzey fine sand (sandy, siliceous, hyperthermic Arenic Endoqualdfs). Treatments were arranged in a randomized complete block design with 4 replications. In 2012, plots were a single crop row and 6.1 m long. In 2013, plots were two rows wide (1 m) and 6.1 m long; one row was a nontreated bo February 7, 2012 and February 1, 2013. The herbicide treatments are listed in the accompanying tables and the nontreated plots were kept weed free by hand weeding and hoeing when weeds were le ss than 7.6 cm tall. A grower standard herbicide program of pendimethalin + metribuzin was used to compare current practices to the herbicide programs under evaluation. PRE treatments were applied on March 2, 2012 and March 1, 2013. Due to warm temperature s in 2012, the potato had reemerged after boarding off and before the PRE application. Emerged potatoes were recovered with soil prior to the PRE application POST treatments were applied March 30, 2012 and April 15, 2013 when the potato was 30 cm tall. Al l POST treatments were applied with NIS at 0.1% v/v. All PRE and POST herbicides were applied with a CO 2 pressurized backpack sprayers with 8004VS nozzles (TeeJet Technologies, Wheaton, IL) calibrated to deliver 280 L ha 1 of spray solution. Foliar injur y to the potato was measured using a visual evaluation ( 0%= no injury, 100%= complete plant death) weekly following PRE applications in the tolerance study. P otatoes were allowed to die naturally and whole plots were harvested for yield by grade and weight Tubers were sorted by grade according to diameter and t ubers identified as having growth disorder s such as growth cracks, misshapen, green, or

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45 rotten wer e sorted and analyzed separately. The grades used were C (1.27 cm 3.81 cm), B (3.81 cm 4.76 cm), A1 (4.76 cm 6.35 cm), A2 (6.35 cm 8.38 cm), A3 (8.38 cm 10.16 cm), and A4 (>10.16 cm). Marketable yield was calculated as the total combined weight of the B to A4 grades (>3.81 cm). Control Study Weed control was evaluated i n two different commercial fie lds operated by Blue Sky Farms Elkton, FL, during 2012 and 2013. Soil types were a Pomona fine sand (sandy, siliceous, hyperthermic Ultic Alaquods) and a Riviera fine sand (loamy, siliceous, active, hyperthermic Arenic Glossaqualfs) in 2012 and 2013, res pectively. In 2012, the d ominant weeds were yellow nutsedge, common ragweed, and bermudagrass. In 2013, t he only weed present was large crabgrass ( Digitaria sanguinalis L. Scop.). The experimental design was a randomized complete block design with four re plications. Plots were 2 rows wide (1m between row spacing ), the first row was a nontreated border and the second was treated. In 2012, plots were 9 m long and in 2013 plots were 6.1 m long. Herbicide t reatments were the same as the tolerance study; howeve r, the weeds remained in the nontreated plots. PRE herbicides were applied on March 29, 2012 and April 15, 2013. POST herbicides were applied when the potato plants were approximately 30 cm tall on May 3, 2012 and May 23, 2013 Ap plications were made using CO 2 pressurized backpack sprayers with 8004VS nozzles (TeeJet Technologies, Wheaton, IL) calibrated to deliver 280 L ha 1 Cultural management at all locations was consistent with University of Florida recommend ations ( Zotarelli et al. 2012 )

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46 Weed control of the treated plot area was visually assessed (0%= no control, 100%= no weeds present ) weekly following PRE application for the efficacy study. Plots were compared to that of the weedy non treated control for assessment. Data analysis. Crop injury, yield, and weed control were analyzed with a general linear model and means were separated using contrasts were used to separate means with statistical significance reported at P = 0. 0 01, 0.05, and 0.10. Both pairwise and non pairwise orthogonal contrasts were used to compare groups of systems which are inherent in the design of the experiment and should be analyzed together to determine their significance against other groups of differing treatm ents (Swallow 1984). Results and Discussion Tolerance Study Minimal potato injury was observed early in the season, however both years of the study experienced unusual weather conditions. Injury did not exceed 5% for any of the herbicides (data not shown). In 2012, potato injury at 7 DAT (<5%) was observed in the tank mixture of fomesafen+ s metolachlor+ metribuzin. Treatments containing fomesafen did show greater injury (<2%) than the non treated control; this was a result of the early potato emer gence as described previously. Leaf necrosis, malformation, and slight chlorosis were observed in plots with fomesafen injury in 2012. In 2013, injury at 21 DAT was observed from s metolachlor alone at 1602 g ha 1 (<5%). This injury is attributable to the cool conditions exhibited in 2013 occurring just after application resulting in a slight stunting and malformation of the leaves. No injury was observed from 28 DAT until harvest for any of the herbicides. Potato tuber yield were not different

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47 for herbici de treatments (Table 4 1). Growth disorders, which did occur, were not an effect of the treatment but of the weather conditions or cultural management, and are expected in this type of system. Control Study Differences in weed populations between the two experimental years required the data to be separated by year. In 2012, poor potato seed quality resulted in a poor crop stand and allowed for unusually high weed populations growing with little competition from the crop (Radosevich 1987). Treatments co ntaining a PRE application had significantly greater yellow nutsedge control than the nontreated control and POST only treatments (Table 4 2). Weed control at 35 DAT was highest in s metolachlor + fomesafen tank mixture treatments (>5%) while not signifi cantly different from the other treatments PRE herbicides. High weed densities and moderate to good control of the present species by the herbicides, as detailed in the label, is the cause for such low control at 35 DAT (Anonymous 2009, Anonymous 2012). A t 42 DAT or 7 days following the POST applications, increased weed control was observed as compared to the previous rating. Fomesafen at 561 g ha 1 f.b. imazosulfuron at 263 g ha 1 had the greatest control, while still unacceptably low (9%). At 62 DAT, all PRE alone treatments and the nontreated had significantly less weed control than imazosulfuron at either rate (<40%). Fomesafen at 280 g ha 1 fb. imazosulfuron and imazosulfuron alone (263 g ha 1 ) had greater control, 80% and 78% respectively (Table 4 2). Fomesafen f.b. imazosulfuron had greater control at 62 DAT than s metolachlor f.b. imazosulfuron. Orthogonal contrast indicated no difference between treatment with either s metolachlor or fomesafen at 7 to 42 DAT. At 35 DAT, comparison between imazosul

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48 demonstrating the residual control of the PRE application was greater than imazosulfuron alone which had not been treated with imazosulfuron yet. Contrasts between fomesafen alone an d s metolachlor alone or f.b. imazosulfuron had significant different late in the season, indicating imazosulfuron as the primary herbicide controlling the weeds late in th e season. Pendimethalin + metribuzin (grower standard) had similar control to the other PRE herbicides early in the growing season, 7 and 35 DAT, however, this was lower than a herbicide program including fomesafen or s metolachlor f.b. imazosulfuron. In 2 013, no weed emergence occurred at 7 DAT resulting in no comparison to the 2012 control study. At 14 DAT, fomesafen tank mixed with s metolachlor provided the greatest control (100%) and similar to all the treatments that include a PRE herbicide except s metolachlor alone at 1602 g ha 1 and fomesafen at 280 g ha 1 f.b. imazosulfuron (Table 4 3). The pendimethalin + metribuzin (grower standard) also had greater control (99%) than all other treatments. The application of imazosulfuron provided no benefit to large crabgrass control. At 56 DAT, no increase in large crabgrass control was observed by applying imazosulfuron, however, all treatments with a PRE application had significantly greater control then the imazosulfuron alone and weedy control (>65%). Contr asts at each of the rating dates only showed significance the PRE application was the only factor that controlled the weed populations. In this study, fomesafen and s metolachlor applied as preemergence herbicides and imazosulfuron as a postemergence herbicide provided excellent crop tolerance with

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4 9 no reduction in total yield. Imazosulfuron alone and s metolachlor crop tolerance is similar to other studies (Felix an d Boydston 2010). Weed control was variable depending on weed species and potato population. Fomesafen followed by imazosulfuron provided good broad spectrum control of susceptible weed species. The use of either a tank mixture of multiple herbicides prov ided similar weed control to other treatments but no additional benefit as compared to other studies which indicated the co application of fomesafen and s metolachlor increased weed control (Peachey et al. 2012). Season long weed control under a mixed bro adleaf, grass, and sedge population can only be achieved using both PRE and POST emergence applications. Reductions in potato tuber yield from season long competition indicates a strong need for a PRE application for early season weed populations (Nelson and Thoreson 1981). The critical weed free period is 6 weeks in potato (Thakral et al. 1989). POST applications in this system are 6 weeks after planting, making it unnecessary to apply a postemergence herbicide to reduce competition with the potato. Howev er, a POST herbicide would be necessary to reduce complications with digging equipment or reducing weed seed contributions to the weed seed bank (Benvenuti 2007). The results of this study provide producers with alternative herbicides that include differe nt modes of action and broader spectrum of controlled weed species with minimal impact on potato growth and yield

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50 Table 4 1. Effect of s metolachlor and fomesafen followed by imazosulfuron on potato yield and tuber growth disorders in 2012 and 2013. G rade (kg) Growth Disorders (kg) Herbicide Rate Timing C B A1 A2 A3 Mkt Yield Green GC a MIS Rotten g ha 1 kg plot 1 Nontreated 0.22 b 0.99 9.52 1.62 0.63 12.76 0.56 0.07 0 1.86 Fomesafen 280 PRE 0.25 1.03 8.68 2.05 0.46 12.2 0.21 0.1 0 1.29 Fomesafen 561 PRE 0.25 0.9 10.42 2.16 0.76 14.23 0.37 0.07 0.05 1.71 S metolachlor 1068 PRE 0.22 1.05 10.08 2.69 1.13 14.95 0.45 0.15 0.02 2.27 S metolachlor 1602 PRE 0.26 0.97 8.17 1.46 0.46 11.05 0.36 0.15 0.01 1.94 Imazosulfuron 263 POST 0.19 1 9.75 2.29 0.68 13.71 0.29 0.13 0.05 1.21 Imazosulfuron 315 POST 0.25 0.92 10.97 2.08 0.3 14.27 0.35 0.08 0.03 1.98 Fomesafen f .b. i mazosulfuron 280 263 PRE POST 0.24 1.09 10.81 2.41 0.76 15.07 0.28 0.1 0 1.95 Fomesafen f .b. i mazosulfuron 561 263 PRE POST 0.26 1.22 9.87 1.86 0.5 13.44 0.24 0.05 0 2.09 S metolachlor f .b. i mazosulfuron 1068 263 PRE POST 0.27 0.96 9.94 2.51 0.98 14.39 0.5 0.22 0.1 2.05 S metolachlor f .b. i mazosulfuron 1602 263 PRE POST 0.2 0.93 8.46 2.17 0.98 12.54 0.62 0.22 0 2.32 Pendimethalin + m etribuzin 798 210 PRE PRE 0.15 0.96 10.17 2.57 1.1 14.79 0.45 0.07 0.03 1.81 Fomesafen + S metolachlor + m etribuzin 280 1182 263 PRE PRE PRE 0.26 0.97 11.04 2.39 1 15.4 0.28 0.12 0.02 1.63 Fomesafen + S metolachlor 280 1068 PRE PRE 0.26 0.79 8.82 2.43 1 13.03 0.81 0.09 0.07 1.51 a GC= growth cracks, MS= misshapen b (p

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51 Table 4 2. Effect of fomesafen and s metolachlor followed by imazosulfuron in potato on weed control evaluation (%) for 2012 cropping season Weed Control Treatment Rate Timing 7 35 42 62 g ha 1 % Nontreated 0 d a 0 0 b 0 d Fomesafen 280 PRE 9 cd 0 1 b 0 d Fomesafen 561 PRE 58 a 4 1 b 0 d S metolachlor 1068 PRE 29 abcd 4 3 b 0 d S metolachlor 1602 PRE 13 d 1 0 b 0 d Imazosulfuron 263 POST 0 d 0 4 b 78 a Imazosulfuron 315 POST 0 d 0 4 b 40 c Fomesafen fb. imazosulfuron 280 263 PRE POST 15 cd 3 4 b 80 a Fomesafen fb. imazosulfuron 561 263 PRE POST 29 abcd 4 9 a 75 ab S metolachlor fb. imazosulfuron 1068 263 PRE POST 26 abcd 1 1 b 54 bc S metolachlor fb. imazosulfuron 1602 263 PRE POST 49 ab 5 4 b 50 c Pendimethalin + metribuzin b 798 210 PRE PRE 21 bcd 1 0 b 0 d Fomesafen + S metolachlor + metribuzin 280 1182 263 PRE PRE PRE 36 abc 5 1 b 0 d Fomesafen+ S metolachlor 280 1068 PRE PRE 24 bcd 6 1 b 0 d Contrasts Fomesafen vs. S metolachlor NS c NS NS ** Fomesafen alone vs. f.b. imazosulfuron NS NS ** *** S metolachlor alone vs. f.b. imazosulfuron NS NS NS *** Imazosulfuron alone vs. following a PRE ** ** NS NS Grower standard vs. new program b NS NS ** *** a Values with the same letter are statistically similar to each other within the same column according to LSD b Grower standard contains pendimethalin + metribuzin PRE c NS= not significant, ***

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52 Table 4 3. Effect of s metolachlor and fomesafen followed by imazosulfuron in potato on large crabgrass control evaluation (%) for 2013 cropping season. Weed Control Treatment Rate Timing 14 35 42 56 g ha 1 -------------------------------------------% ----------------------------------Nontreated 0 d a 0 c 0 d 0 d Fomesafen 280 PRE 98 abc 95 ab 84 bc 73 bc Fomesafen 561 PRE 96 abc 96 ab 94 abc 91 ab S metolachlor 1068 PRE 94 abc 100 a 99 a 94 ab S metolachlor 1602 PRE 93 bc 93 ab 88 abc 81 abc Imazosulfuron 263 POST 0 d 0 c 0 d 1 d Imazosulfuron 315 POST 0 d 0 c 0 d 0 d Fomesafen fb. i mazosulfuron 280 263 PRE POST 91 c 89 b 80 c 65 c Fomesafen fb. i mazosulfuron 561 263 PRE POST 94 abc 98 a 98 ab 96 ab S metolachlor fb. i mazosulfuron 1068 263 PRE POST 96 abc 100 a 100 a 99 a S metolachlor fb. i mazosulfuron 1602 263 PRE POST 96 abc 100 a 100 a 93 ab Pendimethalin + m etribuzin 798 210 PRE PRE 99 ab 98 a 98 ab 96 ab Fomesafen + S metolachlor + m etribuzin 280 1182 263 PRE PRE PRE 98 abc 98 a 94 abc 88 abc Fomesafen+ S metolachlor 280 1068 PRE PRE 100 a 99 a 99 a 99 a Contrasts Fomesafen vs. S metolachlor NS c NS NS *** NS * NS Fomesafen alone vs. f.b. imazosulfuron NS NS NS S metolachlor alone vs. f.b imazosulfuron NS NS NS Imazosulfuron alone vs. following a PRE *** *** *** Grower s tandard vs. new program b NS NS NS a Values with the same letter are stat istically similar to each other b Grower standard contains pendimethalin + metribuzin PRE c NS= not significant, ***

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53 CHAPTER 5 CONCLUSION The objective of the first study was to determine the patterns of weed population distribution through in field weed populations and seedbank densities Irrigation furrows contained the highest population of weeds. Those weeds were then disseminated into the crop rows as indicated by the in field weed populations. In field counts were much lower in the crop rows as compared to the irrigation furrow because crop competition reduced the availability of resources for the weeds to grow. Weed seedbank densities amongst the rows and tiers were highly variable and distributions were inconsistent within all of the fields. In fields A and D, the tiers of the inner portion of the fie ld contained greater weed densities than the first tier; fields C and D had densities within the crop rows that were greater than the irrigation furrow. Field B lacked consistency overall with higher populations at both the irrigation furrow and the fifth crop row. the field, such as the irrigation furrow, however this was not consistent. The weed seedbank provided information on all possible weeds that could impact the potat o fields if given the proper conditions, but did not provide information on how weeds are arranged in this type of production system. While it was not possible to directly correlate weed seedbank populations to in field populations, the use of an adjusted weed seedbank density helped to determine species trends within the fields. Further research needs to be conducted to evaluate the effect of the distribution o f in field weed populations on other abiotic and biotic factors in this system; the res ults of th is study will help determine problematic weed species in potato as well as the location of the higher density and more diverse weed populations within seepage irrigated fields.

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54 The second study of this thesis was the development of new herbicide based sea son long weed control programs. The use of fomesafen PRE, S metolachlor PRE, and imazosulfuron POST had excellent potato tolerance, with no affect on the total marketable yield. Weed control efficacy was strongly dependent upon weed species. Overall, the g reatest season long weed control was observed in the treatments containing either S metolachlor or fomesafen PRE when followed by imazosulfuron POST. Both S metolachlor and fomesafen had excellent residual control of weeds. For situations with a large di versity of weed species such as broadleaves, sedges, and/or grasses, fomesafen and S metolachlor application provided excellent early season control. However, when grasses are the only or most abundant weed species, the application of S metolachlor was b etter than the other treatments. Imazosulfuron POST was only controlling emerged broadleaf and sedge species; emerged grasses were not controlled. All of the programs performed significantly better then the grower standard or the nontreated control under a mixed population of weed species. The results of this study provide growers with alternative herbicides for controlling a broader weed species population and newer chemistries for preventing herbicide resistance development.

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55 LIST OF REFERENCES Encyclopdia Britannica. Encyclopdia Britannica Online Encyclopdia Britannica Inc. (2012) Web. 16 Dec. 2012. http://www.britannica.com/EBchecked/topic/552838/Solanaceae Alves C, MacRae AW, Hunnicut CJ, Jacoby TP, MacDonald GE, Dittmar PJ (2013) Impact of fallow programs and fumigants on nutsedge ( Cyperus spp.) Management in Plasticulture Tomato. Weed Technol 27: 323 330 Anonymous (2009) Dual II Magnum Herbicide product label. Greensboro, NC: Syngenta Crop Protection, Inc. Anonymous (2011) League Herbicide product label. Walnut Creek, CA: Valent U.S.A Corporation. Anonymous (2011) ProwlH2O Herbicide product label. Research Triangle Park, NC: BASF Corporation. Anonymous (2012) ReflexHerbicide product label. Greensboro, NC: Syngenta Crop Protection, Inc. Bagavathiannan MV, Norsworthy JK, Scott RC (2011) Comparison of weed management programs for furrow irrigated and flood irrigated hybrid rice production in Arkansas. Weed Technol 25:556 562 Bailey WA, Wilson HP, Hines TE (2001) Influ ence of cultivation and herbicide programs on weed control and net returns in potato ( Solanum tuberosum ). Weed Technol 15:654 659 Bailey WA, Wilson HP, Hines TE (2002) Response of potato ( Solanum tuberosum ) and selected weeds to sulfentrazone. Weed Technol 16:651 658 Bailey WA, Hatzios KK, Bradley KW, Wilson HP (2003) Absorpotion, translocation, and metabolism of sulfentrazone in potato and selected weed species. Weed Sci 51:32 36 Ball DA (1992) Weed seedbank response to tillage, herbicides, and crop rotati on sequence. Weed Sci 40:654 659 Ball DA, Miller SD (1990) Weed seed population response to tillage and herbicide use in three irrigated cropping sequence. Weed. Sci. 38:511 517 Bekker RM, Bakker JP, Grandin U, Kalamees R, Milberg P, Poschlod P, Thompsons K, Willems JH (1998) Seed size, shape, and vertical distribution in the soil: indicators of seed longevity. Funct Ecol 12: 834 842

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56 Bellinder RR, Arsenovic M, Shah DA, Rauch BJ (2003) Effect of weed growth stage and adjuvant on the efficacy of fomesafen and bentazon. Weed Sci 51:1016 1021 Benvenuti S (1995) Soil light penetration and dormancy of jimsonweed ( Datura stramonium ) seeds. Weed Sci 43:389 393 Benvenuti S (2007) Weed seed movement and dispersal strategies in the agricultural environment. Weed Biol Manag 7: 141 157 Biniak BM, Aldrich RJ (1986) Reducing velvetleaf ( Abutilon theophrasti ) and Giant Foxtail ( Setaria faberi ) with simulated roller herbicide application. Weed Sci 94: 256 259 Boydtson RA, Vaughn SF (2002) Alternative weed management system s control weeds in potato ( Solanum tuberosum ). Weed Technol 16: 23 28 Brosnan KA, ed. (2011) Encyclopedia of American Environmental History. Vol 3. New York: Facts on File. pp. 1074 1075 B uhler DD, Hartzler RG, Forcella F (1997) Implications of weed seedb ank dynamics to weed management. Weed Sci 45:329 336 Buhler DD, Mester TC (1991) Effect of tillage on the emergence depth of giant ( Setaria faberi ) and green foxtail ( Setaria viridis ). Weed Sci 29:200 203 Cardina J, Sparrow DH (1996) A comparison of metho ds to predict weed seedling populations from the soil seedbank. Weed Sci 44:46 51 Chambers, JC, Macmahon JA (1994) A day in the life of a seed: movements and fates of seeds and their implications for natural and managed systems. Annu Rev Ecol Syst 25:263 2 92 Ciuberkis S, Bernotas S, Raudonius S, Felix J (2007) Effect of weed emergence time and intervals of weed and crop competition on potato yield. Weed Technol 21: 612 617 Colbach N, Forcella F, Johnson GA (2000) Spatial and temporal stability of weed population over five years. Weed Sci 48:366 377 Cousens, RD, Dale MRT, Taylor J, Law R, Moerkerk M, Kembel SW (2006) Causes of pattern in plant communities where environmental change is rapid and species longevity is short. J Veg Sci 17: 599 614 Devlaeminck R, Bossuyt B, Hermy M (2005) Seed Dispersal from a forest into adjacent cropland. Agr Ecosyst Environ 106: 57 64

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57 Dittmar PJ, Byrd S, Zotarelli L, Rowland D, Stall W (2012) Weed management in potato. Gainesville: Universit y of Florida Institute of Food and Agricultural sciences HS195 du Croix Sissons MJ, van Acker RC, Derksen,DA, Thomas AG (2000) Depth of seedling recruitment of five weed species measured in situ in conventional and zero tillage fields. Weed Sci. 48:327 332. Dukes MD, Zotarelli L, Morgan KT (2010) Use of irrigation technologies for vegetable crops in Florida. HortTechnology 20:133 142 ERS, USDA (2012) FAOSTAT [Food and Agriculture Organization of the United Nations]. http://faostat3.fao.org/home/index.h tml#HOME. Accessed: November 11, 2012 Felix J, Boydston RA (2010) Evaluation of imazosulfuron for yellow nutsedge ( Cyperus esculentus ) and broadleaf weed control in potato. Weed Technol 24: 471 477 Felix J, Newberry G (2012) Yellow nutsedge control and red uced tuber production with s metolachlor, halosulfuron plus dicamba, and glyphosate in furrow irrigated corn. Weed Technol 26:213 219 Grundy AC, Mead A, Burston S (1999) Modeling the effect of cultivation on seed monement with application to the prediction of weed seedling emergence. J Appl Ecol 36: 663 678 Guillemin JP, Chauvel B (2011) Effects of the seed weight and burial depth on the seed behavior of common ragweed ( Ambrosia artemisiifolia ). Weed Biol Manag 11: 217 223 cent weed control, weed management, and integrated weed management. Weed Technol 27: 1 11 Henry GM, Sladek BS, Hephner AJ, Cooper T (2012) Purple nutsedge ( Cyperus rotundus ) control in bermudagrass turf with imazosulfuron. Weed Technol 26: 304 307 Hutchinson PJS (2002) Herbicide effectiveness on weeds in potatoes. Pages 176 187 in RD Williams, D Ball, TL Miller, R Parker, JP Yenish, TW Miller, DW Morishita, and PJS Hutchinson, eds. Pacific Northwest Weed Control Handbook. Corvallis, OR: Oregon Stat e University Hutchinson PJ, Beutler BR, Farr J (2011) Hairy nightshade ( Solanum sarrachoides ) competition with two potato varieties. Weed Sci 59: 37 42 Hutchinson PJ, Eberlein CV, Tonks DJ (2004) Broadleaf weed control and potato crop safety with postemerg ence rimsulfuron, metribuzin, and adjuvant combinations. Weed Technol 18: 750 756

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58 Isaac RA, Guimaraes SC (2008) Seed bank and above ground weed. Planta Daninha 26:521 530 Klingman GC, Ashton FM (1975) Weed Science: Principles and Practices. New York: Joh n Wiley & Sons. 20 p Locascio SJ (2005) Management of irrigation for vegetables: past, present, and future. HortTechnology 15: 482 485 Makarian H, Rashed Mohassel MH. Bannayan M, Nassiri M (2006) Soil seed bank and seedling populations of Hordeum murinum and Cardaria draba in saffron fields. Agr Ecosyst Environ 120:307 312 Marshall EJP (1988) Field scale estimates of grass weed populations in arable land. Weed Res 28: 191 198 Marshall EJP(1989) Distribution patterns of plants associated with arable fiel d edges. J Appl Ecol 26:247 257 Mulder TA, Doll JD (1993) Integrating reduced herbicide use with mechanical weeding in corn ( Zea mays ). Weed Technol 7: 382 389 Nelson DC, Thoreson MC (1981) Competition between potatoes ( Solanum tuberosum ) and weeds. Wee d Sci 29: 672 677 Pack JE, White JM, Hutchinson CM (2003) Growing potatoes in the Florida home garden. Gainesville: University of Florida Institute of Food and Agricultural Sciences. HS933 Peachey E, Doohan D, Koch T (2012) Selectivity of fomesafen based systems for preemergence weed control in cucurbit crops. Crop Prot 40:91 97 Radosevich SR (1987) Methods to study interactions among crops and weeds. Weed Technol 1:190 198 Rahman A, James TK, Grbavac N (2001) Potential of weed seedbanks for managing weeds: a review of recent New Zealand research. Weed Biol Manag 1:89 95 Rew LJ, Cussans GW (1997) Horizontal movement of seeds following tine and plough cultivation: implications for spatial dynamics of we ed infestations. Weed Res 37: 247 256 Riar DD, Norsworthy JK (2011) Use of imazosulfuron in herbicide programs for drill seeded rice ( Oryza sativa ) in the mid south United States. Weed Technol 25: 548 555 Rouse CE, Dittmar PJ, MacDonald GE, Zotarelli L (2 014) Effect of weeds in seepage irrigation furrows in weed seedbank in potato. Weed Sci (Submitted)

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59 Sensemen, SA, ed (2007) Herbicide Handbook. 9 th ed. Lawrence, KS: Weed Science Society of America. pp. 91 92,207 208,275 278 Stall WM, Sherman M (1983) Potato Production in Florida. University of Florida Digital Collections Circular 118. Stephenson IV DO, Patterson MG, Faircloth WH, Lunsford JN (2004) Weed management with fomesafen preemergence in glyphosate resistant cotton. We ed Technol 18:680 686 Sutton KF Lanini WT, Mitchell JP, Miyao EM, Shrestha A (2006) Weed control, yield, and quality of processing tomato production under different irrigation, tillage, and herbicide systems. Weed Technol 20: 831 838 Taylor SE, Oliver LR (1997) Sicklepod ( Senna obtusifolia) seed production and viability as influenced by late season postemergence herbicide applications. Weed Sci 45: 497 501 Thakral KK, Pandita ML, Khurana SC, Kalloo G (1989) Effect of time of weed removal on growth and yield of potato. Weed Res 29: 33 38 Tonks DJ, Eberlein CV, Guttieri MJ (2000) Preemergence weed control in potato ( Solanum tuberosum ) with ethalfluralin. Weed Technol 14: 287 292 United States Department of Agriculture, Economic Research Service. Potatoes (2012) http://www.ers.usda.gov/topics/crops/vegetables pulses/potatoes.aspx. Accessed: November 11, 2012. USDA NASS. [U.S. Department of Agriculture, National Agricultural Statistics Service] (2013) Crop Production Annual Survey. pp. 56 59. Vangessel MJ, Renner KA (1990) Redroot pigweed ( Amaranthus retroflexus ) and barnyardgrass ( Echinochloa crus galli ) interference in potatoes ( Solanum tuberosum ). Weed Sci 38: 338 343 Wiles LJ, Oliver GW, York AC, Gold HJ, Wilkerson GG (1992) Spatial distribution of broad leaf weeds in North Carolina soybean ( Glycine max ) fields. Weed Sci 40:554 557 Zotarelli L, Roberts PD, Dittmar PJ, Webb SE, Smith SA, Santos BM, Olson SM (2012) Potato Production in Florida. Gainesville: University of Florida Institute of Food and Agricu ltural Sciences. Vegetable Production Handbook 2012 2013 2HS733

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60 BIOGRAPHICAL SKETCH Christopher Edward Rouse was born and raised in Homestead, FL. His first interest in agriculture came his junior year of high school where he was taught the basics of vegetable and nursery production. He graduated Summa c um Laude in 2008 from South Dade Se nior High School. In the spring of 2012, Chris began working on his Bachelor of Science degree majoring in Horticultural Sciences and specializing in horticultural production. Chr is officially began his Master of Science degree in the Fall of 2012 in the Horticultural Sciences Department at the University of Florida. Upon graduation, Chris plans to pursue a Doctor of Philosophy degree specializing in Weed Sciences.