FOMESAFEN PERSISTENCE, MOVEMENT, AND EFFICACY FOR NUTSEDGE CONTROL IN FLORIDA PLASTICULTURE PRODUCTION
By
THOMAS VERNON REED
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2017 © 2017 Thomas Reed To Robin ACKNOWLEDGMENTS
I would like to express my gratitude to family, friends, and fellow graduate students for their support. I would also like to thank my major professor, Dr. Nathan Boyd, my committee members: Dr. Peter Dittmar, Dr. Kelly Morgan, and Dr. Chris Wilson as well as the staff in the
Department of Crop and Soil Sciences that assisted me throughout my graduate program.
4 TABLE OF CONTENTS
page
ACKNOWLEDGMENTS ...... 4
LIST OF TABLES...... 8
LIST OF FIGURES ...... 10
LIST OF ABBREVIATIONS...... 11
ABSTRACT...... 12
CHAPTER
1 LITERATURE REVIEW ...... 14
Purple and Yellow Nutsedge ...... 14 Purple and Yellow Nutsedge Management in Plasticulture ...... 18 Fallow Period...... 18 Fumigation ...... 19 Preemergence Herbicides...... 20 Fomesafen...... 22 Fomesafen Behavior and Dissipation in Soil...... 25 Objective...... 30
2 APPLICATION TIMING INFLUENCES PURPLE AND YELLOW NUTSEDGE SUSCEPTIBILITY TO EPTC AND FOMESAFEN ...... 35
Introduction...... 35 Material and Methods...... 37 Purple Nutsedge...... 37 Yellow Nutsedge...... 38 Data Collection ...... 39 Statistical Analysis...... 40 Results and Discussion ...... 40 Purple Nutsedge...... 40 Yellow Nutsedge...... 42
3 EVALUATION OF FOMESAFEN DOSE RESPONSE ON PURPLE NUTSEDGE TUBERS...... 50
Introduction...... 50 Material and Methods...... 52 First Experiment...... 53 Second Experiment ...... 53 Third Experiment...... 53
5 Data Collection and Analysis...... 53 Results and Discussion ...... 54 First Experiment...... 54 Second Experiment ...... 55 Third Experiment...... 56
4 PERSISTENCE AND MOVEMENT OF FOMESAFEN IN FLORIDA STRAWBERRY PRODUCTION ...... 60
Introduction...... 60 Material and Methods...... 62 Soil Sampling and Analysis...... 64 Soil Moisture...... 65 Statistical Analysis...... 66 Results and Discussion ...... 66 Strawberry Tolerance...... 66 Fomesafen Persistenc and Movement...... 67
5 EFFECT OF FUMIGATION ON FOMESAFEN DISSIPATION ...... 73
Introduction...... 73 Material and Methods...... 74 Results and Discussion...... 78 Fomesafen Dissipation...... 78 Eggplant Tolerance ...... 79 Nutsedge Control ...... 80
6 EVALUATION OF PLASTIC MULCH ON FOMESAFEN DISSIPATION ...... 85
Introduction...... 85 Material and Methods...... 87 Results and Discussion...... 91 Fomesafen Dissipation...... 91 Squash Tolerance...... 92 Nutsedge Control ...... 93
7 EFFECT OF INCORPORATING FOMESAFEN FOR CONTROLLING PURPLE AND YELLOW NUTSEDGE IN PLASTICULTURE ...... 101
Introduction...... 101 Material and Methods...... 102 Greenhouse Experiment...... 102 Field Experiment...... 104 Statistical Analysis...... 105 Results and Discussion ...... 106 Greenhouse Experiment...... 106 Field Experiment...... 107
6 8 CONCLUSION...... 111
LIST OF REFERENCES...... 114
BIOGRAPHICAL SKETCH ...... 125
7 LIST OF TABLES
Table page
2-1 Purple and yellow nutsedge shoot number per pot and average shoot length when herbicides were applied in two combined greenhouse experiments for purple and yellow nutsedge, Gainesville, FL in 2014 and Balm, FL in 2015, respectively...... 45
2-2 Purple nutsedge average emergence per pot, shoot height, leaf number, dry shoot mass per pot, and injury four weeks after planting from EPTC and fomesafen applications at six timings in two combined greenhouse experiments, 2014, Gainesville, FL...... 46
2-3 Yellow nutsedge average emergence per pot, shoot height, leaf number, dry shoot mass per pot, and injury four weeks after planting from EPTC and fomesafen applications at six timings in two combined greenhouse experiments, 2015, Balm, FL...... 48
3-1 Purple nutsedge tuber sprouting, tuber viability, and dry sprouted growth biomass after exposure to fomesafen with or without tuber imbibition in two combined growth chamber experiments, 2016, Balm, FL...... 58
3-2 Purple nutsedge tuber sprouting, tuber viability, injury, and dry sprouted growth mass after exposure to fomesafen concentrations and light in two combined growth chamber experiments, 2016, Balm, FL...... 59
4-1 Rainfall, drip irrigation, and overhead irrigation between soil sampling dates during field experiments, 2014-2015 and 2015-2016, Balm, FL...... 69
4-2 Parameter estimates of fomesafen concentration in soil at 0.0 to 0.1 m depth from field experiments, 2014-2015 and 2015-2016, Balm, FL...... 71
5-1 Rainfall and drip irrigation between soil sampling dates during field experiments, 2015 and 2016, Balm, FL...... 81
5-2 Fomesafen concentrations in soil across nontreated and fumigated fomesafen treatments in field experiments, 2015 and 2016, Balm, FL...... 82
5-3 Eggplant injury after transplant from applications of fumigation and herbicide combinations in combined field experiments, 2015 and 2016, Balm, FL...... 83
5-4 Purple nutsedge density averaged across evaluation dates that were one and two months after treatment of fumigation and herbicide combinations in field experiments, 2015 and 2016, Balm, FL...... 84
6-1 Rainfall and drip irrigation volume between soil sampling dates during field experiments, 2015 and 2016, Balm, FL...... 95
8 6-2 Fomesafen concentrations in soil after preemergence applications of fomesafen at 0.42 kg ai ha-1 under assorted plastic mulches from field experiments, 2015 and 2016, Balm, FL ...... 96
6-3 ‘Sunburst’ squash counts and yield from preemergence fomesafen applications at 0.42 kg ai ha-1 under assorted plastic mulches in field experiments, 2015 and 2016, Balm, FL...... 99
6-4 Purple nutsedge density from preemergence fomesafen applications at 0.42 kg ai ha-1 under assorted plastic mulches in field experiments, 2015 and 2016, Balm, FL ...... 100
7-1 Purple nutsedge average emergence, shoot height, leaf number, injury, and dry shoot mass following fomesafen applications using multiple methods in two combined greenhouse experiments, 2015, Balm, FL ...... 109
7-2 Yellow nutsedge average emergence, shoot height, leaf number, injury, and dry shoot mass following fomesafen applications using multiple methods in two combined greenhouse experiments, 2015, Balm, FL...... 110
9 LIST OF FIGURES
Figure page
1-1 Purple and yellow nutsedge inflorescences ...... 32
1-2 Fomesafen chemical structure...... 33
1-3 An example of Protox inhibition in susceptible plants ...... 34
4-1 Fomesafen concentration in soil at three depth from field experiments, 2014-2015 and 2015-2016, Balm, FL. Error bars represent standard error of the mean ...... 70
4-2 Gravimetric water content in four placements from the center of the bed for three depths at five sampling dates from nontreated control plots, 2014-2015 and 2015- 2016, Balm, FL ...... 72
6-1 Daily average volumetric water content at 0.1 m depth under assorted plastic mulches and rainfall during the experimental period in 2015 and 2016, Balm, FL ...... 97
6-2 Daily average soil temperatures at 0.1 m depth under assorted plastic mulches during the experimental period in 2015 and 2016, Balm, FL ...... 98
10 LIST OF ABBREVIATIONS
CE Collision energy
DAP Days after planting
DAT Days after treatment
EPTC S-ethyl dipropyl carbamothioate
EVOH Ethylene vinyl alcohol
GCREC Gulf Coast Research and Education Center
HPLC High performance liquid chromatography
Koc Soil distribution coefficient based on organic carbon content
LDPE Low-density polyethylene
M Molarity pKa Logarithmic acid dissociation constant ppb Parts per billion
PPFD Photosynthetic photon flux density
Protox Protoporphyrinogen oxidase
Proto IX Protoporphyrin IX
Protogen IX Protoporphyrinogen IX
SRM Selected reaction monitoring
TIF Totally impermeable film
VIF Virtually impermeable film
WAP Weeks after planting
WAT Weeks after treatment
WATr Weeks after transplant
11 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy
FOMESAFEN PERSISTENCE, MOVEMENT, AND EFFICACY FOR NUTSEDGE CONTROL IN FLORIDA PLASTICULTURE PRODUCTION
By
Thomas Reed
May 2017
Chair: Nathan Boyd Major: Horticultural Sciences
Purple (Cyperus rotundus L.) and yellow nutsedge (C. esculentus L.) are problematic weeds in Florida small fruit and vegetable production. Fomesafen is a protoporphyrinogen oxidase inhibitor that has the potential to be used as an alternative mechanism of action for preemergence nutsedge control in the production systems. Greenhouse experiments demonstrated fomesafen treatments have the ability to suppress purple and yellow nutsedge growth with efficacy maximized when applications are conducted at or prior to tuber sprouting.
However, field application showed minimal control of purple nutsedge and tuber viability was unaffected by fomesafen treatments in growth chamber experiments. The incorporation of fomesafen with irrigation or soil tillage did not increase efficacy or result in consistent activity on nutsedge. Fomesafen is unlikely to adequately control purple nutsedge in plasticulture systems at rates registered for use in vegetables, but may have efficacy on other weed species.
There is concern in plasticulture systems that fomesafen may persist at concentrations that injure crops in subsequent growing seasons. Fomesafen tolerance in unregistered crops eggplant (Solanum melngena L.), squash (Cucurbita pepo L.), and strawberry (Fragaria × ananassa Duch.) was observed during field experiments. In the strawberry production system, fomesafen concentration decreased significantly after overhead and drip irrigation began to aid
12 transplant establishment. Fomesafen persistence was unaffected by fumigation with a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha-1. Fomesafen dissipation was reduced with the use of low density polyethylene, virtually impermeable film, and totally impermeable film black/white mulches compared with open field production. At transplant, treatments with black/white mulches had greater than twofold the fomesafen concentrations than treatments with clear or no mulch. Fomesafen treatments with black/white mulches persisted at similar concentrations throughout the entire squash growing season and fomesafen was detected in the 0.0 to 0.1 m depth soil at the end of all experiments.
13 CHAPTER 1 LITERATURE REVIEW
Purple and Yellow Nutsedge
Purple (Cyperus rotundus L.) and yellow (C. esculentus L.) nutsedge are problematic weeds in small fruit and vegetable production in temperate and tropical regions around the world. Purple and yellow nutsedge are natives of Eurasia and North America, respectively
(Bryson 2009a, 2009b). Yellow nutsedge is the most common of the two species in North
America and occurs throughout the continental United States whereas purple nutsedge is limited to southern regions (Radford et al. 1968; Wills 1987).
Purple and yellow nutsedge are in the Cyperaceae family known for growing in damp habitats, with creeping sympodial rhizomes, fibrous roots, triangular stems, and three-ranked leaves (Zomlefer 1994). The Cyperaceae generally are divided into genera and species based on features of the inflorescence and fruit characteristics (Zomlefer 1994). Both species are erect, colonial perennials that reproduce primarily via rhizomes and tubers, with tubers being the primary means of dispersal (Stoller and Sweet 1987). The two species are commonly distinguished from one another by inflorescence, leaf tip, and tuber characteristics (Figure 1-1).
Purple nutsedge has reddish to purple inflorescence and leaves that abruptly taper to an acute tip whereas yellow nutsedge has a yellow to tan inflorescence and leaves that gradually taper to a sharp point (Bryson 2009a, 2009b; Radford et al. 1968). Purple nutsedge tubers are connected in chains by rhizomes and tend to be coarse and oblong (Bryson 2009a; Radford et al. 1968).
Solitary yellow nutsedge tubers are spherical and smooth, terminal from the basal bulb or rhizomes (Bryson 2009b).
Depending on region, purple and yellow nutsedge populations may or may not flower and/or produce viable seeds (Stoller and Sweet 1987). Seed viability may vary in populations,
14 but a significant proportion of the seeds can be viable and persist for extended periods of time.
Despite this, seedlings are rarely observed in the field and it is widely thought that seed production does not play a significant role in the population dynamics of either species (Bryson
2009a, 2009b; Wills 1987; Lapham and Drennan 1990). Tubers of both species present in the soil may remain dormant until receiving the appropriate stimuli, which tends to be temperature in temperate climates and moisture in arid climates (Forcella et al. 2000). In greenhouse conditions, tubers rarely sprout below 10° C or above 45° C with optimal sprouting occurring between 25 and 35° C at constant temperatures (Nishimoto 2001). Field trials have reported very different upper and lower limits. For example, Wilen et al. (1996b) reported base temperatures around 11°
C and upper limits between 25 and 30° C. Holt and Orcutt (1996) also noted that yellow nutsedge had a lower temperature threshold for bud sprouting (6° C) than purple nutsedge (11°
C). Soil moisture plays a critical role in tuber sprouting (Nishimoto 2001). Tubers that have been exposed to dry conditions require a greater number of accumulated growing degree days before emergence (Wilen et al. 1996a). It is also clear that tuber sprouting is enhanced with temperature fluctuations (Miles et al. 1996; Sun and Nishimoto 1997). Miles et al. (1996) reported a linear increase in total tubers sprouting with an increase in temperature fluctuations from 0 to 6° C.
Tuber persistence varies with climate and environment but they can remain viable for more than two years (Nishimoto 2001). Tubers that have previously sprouted are able to enter secondary dormancy and persist in the soil until conditions are conducive for sprout growth.
When purple and yellow nutsedge tubers sprout they produce one or multiple determinate rhizomes that grow upwards and form a basal bulb just beneath the soil surface. Each basal bulb gives rise to shoots, fibrous roots, and indeterminate rhizomes which may give rise to secondary basal bulbs, tubers, or additional shoots (Wills 1987). The majority of roots tend to rise from the
15 tuber in purple nutsedge and from the basal bulb in yellow nutsedge (Obrigawitch 1980). Shoots emerge, grow, and flower within seven to eight weeks of emergence (Hauser 1962). The shoot of both species consists of a stem-like triangular grouping of leaves (Wills 1987). As the plant matures, a solid triangular stem extends through the leaves and produces an inflorescence (Wills et al. 1980). Tuber formation begins four to six weeks after seedling emergence with tuber chains in purple nutsedge developing 10 weeks after emergence (Hauser 1962; Stoller and Sweet 1987).
Yellow nutsedge tubers are not produced in chains but are generally singularly produced at the terminal end of a rhizome. Many different ecotypes of purple and yellow nutsedge have been reported (Wills 1987). Ecotypes can vary in a wide range of morphological characteristics including size, color, height and tuber size (Stoller and Sweet 1987). Purple and yellow nutsedge tubers are able to produce multiple shoots and tubers within a single season. Tumbleson and
Kommedahl (1961) reported that one yellow nutsedge tuber could give rise to a patch with a 2.1 m diameter that contained 1,900 plants and 6,900 tubers within a single growing season.
Light and temperature impact nutsedge growth and reproduction. Stoller and Woolley
(1983) found that temperature fluctuations were the primary stimulus of yellow nutsedge basal bulb formation with a fluctuation of 10° C required for basal-bulb differentiation. They also found that light stimulated basal bulb formation in the absence of a 10° C fluctuation in temperature. Both species possess C4 photosynthetic characteristics and as a result are sensitive to shade and relatively poor competitors for light (Stoller and Sweet 1987). Shading can reduce production of leaf area, dry matter, rhizomes, and tubers (Patterson 1982). In low light conditions both species partition plant biomass to shoots at the expense of rhizome and tuber formation
(Santos et al. 1997b). At higher temperatures, purple nutsedge growth is correlated with incoming radiation, which suggests that shade may be an effective tool to minimize growth and
16 reproduction (Wills 1975). Shaded purple nutsedge individuals produce fewer tubers over an entire season compared to individuals grown without a competing crop (Neeser et al. 1997a,
1997b). Keeley and Thullen (1978) also found that the average number of yellow nutsedge shoots, tubers, and total dry matter was linearly correlated with light interception.
Purple and yellow nutsedge are especially problematic in crops grown in plasticulture systems due to their ability to penetrate the plastic mulch. In fact, purple nutsedge growth is promoted by black polyethylene mulch and a single sprouted tuber under the mulch can give rise to a patch 16.1 m2 with 1,550 shoots within 32 weeks of planting (Webster 2005b). However, black polyethylene mulch can reduce yellow nutsedge shoot and tuber production (Daugovish and Mochizuki 2010; Webster 2005a). This suggests purple nutsedge may be a more problematic species to control in Florida plasticulture production.
Weed pressure has a significant effect on crop yield, quality, and production costs.
Competition between plants occurs above and below ground and begins even before resources are limiting (Rajcan et al. 2004; Schenk 2006). Season long interference from purple nutsedge at a density of 200 shoots m-2 reduced bell pepper (Capsicum spp.) fruit yield up to 32% (Morales-
Payan et al. 1997). Dense populations of nutsedge can reduce pepper yield by 70 to 73% and tomato yield by 51% (Gilreath and Santos 2004a; Morales-Payan et al. 1998; Motis et al. 2003).
The impact on yield depends on nutsedge density, timing of competition, and resource availability (Motis et al. 2003, Morales-Payan et al. 2003). Other studies have found that competition increases when nutsedges emerge earlier and are closer to the crop (Motis et al.
2003; Morales-Payan et al. 2003). Morales-Payan (2003) reported that below ground competition had a greater impact on tomato yield than above ground competition.
17 Purple and Yellow Nutsedge Management in Plasticulture
Fallow Period
In Florida plasticulture production growers typically supplement in season weed control with herbicides, cultivation, cover crops, or a combination of herbicides and cultivation during fallow periods. Nutsedge management during the fallow period is important because tuber numbers can increase substantially during poorly managed fallow periods and lead to increased pressure in the following vegetable crop (Miller et al. 2014). This is especially true during the summer months when high temperatures, high soil moisture, and low soil nitrogen favor tuber formation (Garg et al. 1967). Dense fast-growing cover crops compete with shade intolerant nutsedge reducing growth and reproduction (Neeser et al. 1997a; Patterson 1982; Stoller and
Sweet 1987). Glyphosate is the most common herbicide applied during fallow periods and it can reduce tuber production (Nelson and Renner 2002; Webster et al. 2008). Glyphosate can also be used in season for spot spraying and controlling nutsedge on field edges. Zandstra et al (1974) reported that repeated glyphosate applications reduced tuber production by 92%. However, glyphosate efficacy and movement within the plant varies with plant age with fewer tubers killed in older plants (Zandstra and Nishimoto 1977). Application timing is critical to maximize herbicide efficacy and ensure tuber production does not occur between treatments. Application timing affects where and to what extent herbicides move as well as the level of control achieved.
The best control is typically achieved when cultivation is combined with glyphosate applications
(Alves et al. 2013). Cultivation can break up tuber chains and dormancy stimulating nutsedge emergence. The newly emerged shoots can be controlled with subsequent herbicide applications.
18 Fumigation
Historically, fruit and vegetable growers in Florida have relied on methyl bromide as the foundation for all pest management including weeds, nematodes, and soilborne pathogens
(Chandler et al. 2001). In 1993, methyl bromide was classified as an ozone depleting substance under the provisions of an international treaty known as the Montreal Protocol and in 2013 its use was prohibited in all fruit and vegetable crops in Florida. Many alternative fumigants have been registered in Florida small fruit and vegetable production that control or suppress nutsedge.
For example, Gilreath and Santos (2004a) reported a 90% reduction in purple nutsedge density compared with the nontreated control 10 weeks after transplanting (WATr) tomatoes (Solanum lycopersicum L.) when a combination of 83% 1,3-dichloropropene and 17% chloropicrin at 392 kg ha-1 was applied. McAvoy and Freeman (2013a) reported up to 100% yellow nutsedge control with reduced rates of dimethyl disulfide under impermeable films 10 WATr. Despite this apparent success, the majority of Florida growers report poor or inconsistent nutsedge control with the alternative fumigants compared to methyl bromide. They also report that purple and yellow nutsedge density has increased following the loss of methyl bromide (Snodgrass et al.
2011). These observations were supported by a three-year trial conducted by Jacoby (2012) at the University of Florida. He evaluated four methyl bromide fumigant alternatives and found that nutsedge density increased over time in all treatments. Fumigants may only provide short-term nutsedge control and issues with coverage throughout the bed are a concern when drip applied
(Chase et al. 2006; Jacoby 2016). Herbicide use with fumigants has been demonstrated to increase nutsedge control compared to fumigation alone. Gilreath and Santos (2004b) reported an increase in purple nutsedge control at 16 and 50 days after treatment (DAT) when metolachlor at 2.25 kg ha-1 was applied with a combination of 83% 1,3-dichloropropene and 17%
19 chloropicrin at 410 kg ha-1 compared with the fumigant alone as density was reduced greater than 90%. The addition of metolachlor at 1.1 and 2.3 kg ha-1 reduced purple nutsedge density
71% and 91%, respectively, at 12 weeks after treatment (WAT) compared to 1,3- dichloropropene and chloropicrin alone (Gilreath and Santos 2005a). Supplementary herbicide use with alternative fumigants can achieve similar weed control to methyl bromide treatments.
Santos (2009) observed no difference in nutsedge densities between a methyl bromide and chloropicrin combination compared with herbicides napropamide plus S-metolachlor or EPTC application followed by drip applied metam potassium. Preemergence herbicides used in combination with fumigants may facilitate season-long weed control in plasticulture production.
Preemergence Herbicides
Preemergence herbicides including EPTC, halosulfuron, and S-metolachlor with demonstrated activity on nutsedge have been registered for use in Florida plasticulture production, but have not been universally adopted because of inconsistent efficacy and concern over crop tolerance. EPTC is a thiocarbamate herbicide that inhibits cuticle formation at the early stages of germination with most susceptible plants failing to emerge (Fuerst 1987; Shaner 2014).
Halosulfuron inhibits acetolactate synthase, an enzyme in branched chain amino acid production, and contacted emerging seedlings becoming necrotic (LaRossa and Schloss 1984; Shaner 2014).
S-metolachlor is a chloroacetanilide herbicide that inhibits very long chain fatty acid biosynthesis preventing weed emergence (Böger et al. 2000; Shaner 2014). The herbicides have demonstrated varied levels of purple and yellow nutsedge suppression in open field production systems. Purple nutsedge tuber sprouting was reduced 44% 2 WAT of EPTC at 4.48 kg ai ha-1
(Holt et al. 1962). EPTC at 3.36 kg ai ha-1 reduced yellow nutsedge tuber production 66% and shoot weight 29% compared with the nontreated control 12 WAT (Keeley and Thullen 1974).
20 Grichar et al. (2003) reported preemergence applications of halosulfuron at 0.07 kg ai ha-1 controlled purple nutsedge greater than 90%. Webster and Grey (2014) observed reduced nutsedge tuber production and viability after halosulfuron treatments. Akin and Shaw (2001) reported preemergence S-metolachlor treatments reduced purple and yellow nutsedge total and viable tuber density compared with the nontreated. Preemergence applications of S-metolachlor at 1.4 kg ai ha-1 controlled purple and yellow nutsedge 64% and 70%, respectively, three months after application (Clewis et al. 2007).
Preemergence applications of herbicides during bed formation in Florida plasticulture production systems have had variable success (Boyd 2015; Boyd and Reed 2016; Miller and
Dittmar 2014). In a study looking at preemergence herbicides in tomato production, Boyd (2015) reported S-metolachlor at 1.07 kg ai ha-1 was the only herbicide when applied alone that reduced purple nutsedge density. Boyd and Reed (2016) reported EPTC, halosulfuron, and S-metolachlor treatments reduced purple nutsedge density in one of two years in strawberry producton.
Herbicides such as halosulfuron and S-metolachlor applied under the plastic mulch can reduce nutsedge growth but generally not to the extent desired (Adcock et al. 2008; Boyd 2015; Pereira et al. 1987). This inconsistency is likely due to poor translocation to sites of action, temporary inhibition of tuber sprouting, or inconsistent efficacy at different growth stages and environmental conditions (Obrigawitch et al. 1980; Pereira et al. 1987). Preemergence treatments applied under plastic mulch with adequate efficacy on purple and yellow nutsedge are desirable because they enable rotation of active ingredients to avoid herbicide resistance, reduce the number of passes when applied during the fumigation operation, and they prevent puncture of the plastic mulch facilitating its use with multiple crops. Herbicide options that can be used in
21 conjunction with fumigation or in combination with other herbicides are needed to reduce nutsedge populations over time, especially if tubers are damaged or tuber production is inhibited.
Fomesafen
Fomesafen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-methylsulfonyl)-2- nitrobenzamide, is a diphenylether herbicide that inhibits the protoporphyrinogen oxidase
(Protox) enzyme and is used for weed control in cotton (Gossypium hirsutum L.), soybeans
(Glycine max L. Merr.), snap bean (Phaseolus vulgaris L,) pepper, tomato and potato (Solanum tuberosum L.) (Figure 1-2) (Anonymous 2014; Shaner 2014). Fomesafen is an active ingredient in various products including Syngenta Crop Protection registered Reflex®, which is labeled for use in Florida pepper and tomato plasticulture production.
Symptomology of susceptible plants to fomesafen includes leaf chlorosis, necrosis, and desiccation within three days (Shaner 2014). Uniform coverage of the target site is critical for weed control with Protox inhibiting herbicides and direct contact with emerging weeds is necessary for control in preemergence applications. Fomesafen is rapidly absorbed by leaf tissue within one hour from a postemergence application, and may also be absorbed by the root system and is primarily xylem mobile (Shaner 2014). The tolerance of crops to herbicides that inhibit
Protox depends on herbicide detoxification by the plants or their ability to mitigate the oxidative stress induced by these compounds (Geoffrey et al. 2002; Gullner and Dodge 2000; Jung et al.
2008). Soybean tolerance to fomesafen is due to rapid cleavage of the diphenylether bond, producing inactive metabolites by glutathione transferase enzymes (Andrews et al. 1997; Shaner
2014).
Protox catalyzes the conversion of protoporphyrinogen IX (Protogen IX) to protoporphyrin IX (Proto IX) as part of the tetrapyrrole biosynthesis pathway (Duke et al. 1991;
22 Scalla and Matringe 1994). Tetrapyrroles, such as heme and chlorophyll, serve as cofactors in numerous essential enzymatic and signaling processes in plants including light harvesting, nitrogen fixation, oxygen transport, quenching of free radicals, respiration or phosphorylation, and storage (Beale and Weinstein 1990; Grimm 1999).
The herbicidal effects of Protox inhibitors are relatively quick due to fast build up of substrates rather than from the depletion of chlorophyll (Becerril and Duke 1989). Susceptible species treated with a Protox inhibiting herbicide accumulate a substrate, Proto IX, which leads to cellular damage upon exposure to light (Becerril and Duke 1989; Matringe et al. 1989; Scalla and Matringe 1994; Witkowski and Halling 1989). It is believed that as Protogen IX accumulates above normal levels, it diffuses out of the site of synthesis, and is oxidized nonenzymatically to
Proto IX that is then no longer available for magnesium insertion from magnesium chelatase to continue the chlorophyll biosynthesis pathway (Matringe et al. 1989). Protogen IX and Proto IX are specifically exported by plastids for transfer from chloroplasts for mitochondrial heme synthesis (Jacobs and Jacobs 1993). The export of the accumulating Protogen IX prevents feedback inhibition of the pathway.
The plasma membrane has the capability to oxidize Protogen IX to Proto IX through activity that differs from plastid and mitochondrial protox and does not respond to Protox inhibitor herbicides (Jacobs et al. 1991; Lee and Duke 1994). The lipophilicity of Proto IX is significantly greater than for Protogen IX and it is more likely to remain in membranes in which it is formed causing destruction of plasma membranes (Duke et al. 1991; Duke et al. 1994). Proto
IX in the presence of light and molecular oxygen generates high levels of singlet oxygen as an initiating factor for lipid peroxidation of polyunsaturated fatty acids in the membranes (Scalla and Matringe 1994). Singlet oxygen removes hydrogen from the fatty acids and forms lipid
23 radicals that react with oxygen forming peroxidized lipid radicals, which are able to propagate the reaction by extracting hydrogen from other polyunsaturated fatty acids (Scalla and Matringe
1994). This results in unstable lipid peroxides leading to degradation of the fatty acids and overall membrane integrity (Hess 2000). In brief, the mechanism of action for fomesafen is the inhibition of Protox, causing the accumulation of Proto IX that in the presence of light, leads to lipid peroxidation that results in cell death (Figure 1-3) (Becerril and Duke 1989; Scalla and
Matringe 1994).
Due to the rapid expansion of herbicide resistant weeds in the southern United States to other herbicide mechanisms of action, fomesafen preemergence applications have become an essential component of weed control in cotton and soybean to control a variety of annual broadleaf weeds at 0.28 to 0.42 kg ai ha-1 rates (Shaner 2014; Sosnoskie et al. 2009). Fomesafen has the potential to be used as an alternative mechanism of action for nutsedge control in Florida small fruit and vegetable plasticulture production as well and can be a component of an integrated pest management strategy. Fomesafen preemergence treatments have shown the ability to suppress or control yellow nutsedge growth (Anonymous 2014; Dowler 1987; Wilcut et al. 1997). In plasticulture production, drip applied fomesafen at 0.28 kg ai ha-1 reduced yellow nutsedge punctures of mulch 89% at 56 DAT (Monday et al. 2015). Limited fomesafen efficacy on purple nutsedge has been demonstrated by previous research. In Florida, Miller and Dittmar
(2014) stated preemergence applications of fomesafen 0.42 kg ai ha-1 controlled a mix of purple and yellow nutsedge 48 to 50% at 28 DAT, with 52% nutsedge control at 11 WAT. Fomesafen application alone did not reduce purple nutsedge populations in strawberry production (Boyd
2015; Boyd and Reed 2016).
24 Florida producers apply preemergence herbicides on top of the bed after fumigation prior to laying the plastic mulch. Incorporating fomesafen in plasticulture production may increase efficacy on nutsedge by placing the herbicide closer to tubers allowing for fomesafen to be absorbed shortly after tuber sprouting. Gilreath and Santos (2004b) reported applications of metolachlor at 1.13 kg ai ha-1 and napropamide at 2.25 kg ai ha-1 reduced purple nutsedge density the greater the depth of herbicide incorporation in combination with a fumigant. Preplant- incorporated treatments of fomesafen at 0.28 kg ai ha-1 controlled yellow nutsedge 62% compared to 40% for preemergence treatments at 4 WAT (Wilcut et al. 1991).
Fomesafen Behavior and Dissipation in Soil
Fomesafen breaks down rapidly under anaerobic and low redox potential conditions, and also photodecomposes readily under relatively low sunlight conditions (Shaner 2014). Li (2014) reported lab incubated fomesafen had minimal degradation by soil microorganisms and biological degradation is unlikely to be a major pathway for fomesafen dissipation under aerobic conditions in the field. Fomesafen half-life varies significantly under different environmental and soil conditions. Fomesafen field half-life was reported from 28 to 66 days, after 0.18 kg ai ha-1 alone or 0.09 followed by 0.18 kg ai ha-1 applications with residue still detectable 350 DAT in a
Madalin silty clay loam (Rauch et al. 2007). Fomesafen half-life under anaerobic conditions may be less than three weeks (Shaner 2014). A variable half-life dependent on soil and environmental conditions is similar to other diphenylether herbicides. Half-lives were 9 to 173 days for chlornitrofen, 3 to 87 days for nitrofen and 8 to 64 days for chlomethoxynil (Oymada and
Kuwatsuka 1988). Fomesafen has a longer half-life than other Protox inhibiting herbicides flumioxazin and oxyfluorfen used in plasticulture production (Mueller et al. 2014; Rauch et al.
25 1997; Shaner 2014). Mueller et al. (2014) reported fomesafen half-life over three experimental years on a loam soil averaged 46 days, more than twice as great as flumioxazin.
Due to residual persistence, fomesafen may injure susceptible crops a year after application and has rotational crop plant back intervals as great as 18 months (Anonymous 2014;
Shaner 2014). Cucumber (Cucumis sativus L.) exhibited injury when planted 2 weeks after a
0.28 kg ai ha-1 fomesafen application with injury persisting 11 WAT under open-field conditions
(Johnson and Talbert 1993). Sweet corn (Zea mays L.) grown in areas with higher organic matter and lower pH had greater carry over injury from fomesafen treatments (Rauch et al. 2007). Many growers in Florida double crop, and fomesafen’s potential to persist at a high concentration under plastic may dissuade producers from using the herbicide to avoid limitations on which fruit or vegetable crops can be planted back into beds without fear of injury.
Plastic mulches are used in Florida small fruit and vegetable production to protect raised beds from erosion, decrease soil moisture evaporation, improve fumigant efficacy, extend weed control, and increase soil temperature in the root zone. Pesticide dissipation is affected by plastic mulch, which could influence weed control, crop injury, and pesticide persistence by limiting sunlight, leaching by rainfall, and biological activity (Bond and Walker 1989; Jensen et al.
1989). Bond and Walker (1989) determined dissipation of linuron, pendimethalin, chlorobromuron, and flurochloridone was reduced when applied to soil under perforated polyethylene covers compared with bare soil. It took twice the amount of time for s-metolachlor to dissipate 50% under low-density polyethylene mulch (LDPE) (four days) than bare ground
(two days) (Grey et al. 2007). Fumigation in combination with the use of plastic mulch may also increase herbicide persistence. EPTC half-life was 9 days, but when applied in conjunction with metam sodium under black plastic mulch half-life increased to 22 days (Stiles et al. 2000).
26 Delayed dissipation of pesticides applied to soil under black polyethylene covers has been previously established, however there is a lack of research on fomesafen dissipation in plasticulture production and dissipation of herbicides under virtually impermeable film (VIF) and totally impermeable film (TIF). In Florida production systems, VIF and TIF mulches are most widely used and are multi-layer films which contain barrier polymers such as polyamide
(nylon) or ethylene vinyl alcohol (EVOH) compressed between other layers of polymer that bind the polyethylene outer layer to the barrier layer. Films containing an EVOH barrier layer are currently referred to as TIF (Qin et al. 2011). Films containing barrier polymers are significantly less permeable to fumigants than LDPE and high density polyethylene mulches (Chellemi et al.
2011; Gamliel et al. 1998; Ou et al. 2007; Qin et al. 2011; Santos et al. 2007; Wang et al. 1998).
Gamliel et al. (1998) reported a 100 μm thick LDPE film was over 150 fold more permeable to methyl bromide, than a 30 μm mulch containing an EVOH barrier layer. Besides low fumigant vapor permeation TIF is more resistant to stretching, tearing and puncturing (Qian et al. 2011;
Qin et al. 2011).
Soil properties, adsorption, desorption, mobility and biological degradation are important factors that determine pesticide persistence and bioavailability. Fomesafen is a weak acid with increased sorption at low pH. Bioavailability and solubility of fomesafen in soil is affected by pH
-1 with a logarithmic acid dissociation constant (pKa) equal to 2.7 with solubility of 50 mg L at pH 7 and less than 1 mg L-1 at pH 1 (Shaner 2014, Weber 1993a, 1993b). Acidic soil surfaces may reduce the water solubility, mobility and bioavailability of fomesafen in soil, due to the formation of hydrophobic bonding between fomesafen molecule and lipophilic sites on the organic colloidal surfaces (Weber 1993a). Weber (1993b) suggested for weak acids like fomesafen, adsorption occurred by physical force near neutral pH and hydrophobic bonding or
27 precipitation at low pH. Decreasing soil pH from 6.05 to 3.46 increased imazapyr, a weak acid, adsorption to two soils by 10.9 and 2.6 fold, respectively (Pusino et al. 1997). At soil pH ranges
5 to 8, adsorption to Fe and Al oxides could occur for weak acids because they mainly appear in their anionic forms (Newby and White 1981; Pusino et al. 1997). Across a range of soils
-1 fomesafen soil distribution coefficient based on organic carbon content (Koc) averaged 60 ml g for the sodium salt of the herbicide (Shaner 2014; Wauchope et al. 1992). Guo et al. (2003) reported organic matter and pH were significantly correlated to fomesafen adsorption. Li (2014) reported organic matter, clay, and silt content were inversely related to fomesafen desorption, while pH and sand content were positively related to desorption. Fomesafen has been suggested to have moderate leaching potential (Newby and White 1981). Weissler and Poole (1982) leached fomesafen at 0.3 kg ai ha-1 with 660 mL of water over nine weeks in four soils with 47% to 67% of applied fomesafen remaining at 0 to 10 cm depth in a loam, loamy sand, and silty loam. However, mobility was greater in the coarse sand with 18% of fomesafen remaining at a 0 to 10 cm depth. Weber (1993b) reported fomesafen exhibited higher mobility in a sandier
Norfolk sandy loam than three other soils when irrigated. Guo et al. (2003) concluded 90% of the applied 14C-fomesafen remained in the top 5 cm of a Powdery-loamy paddy soil with 7.6 pH and
0.8% organic matter under field conditions after 60 days. Fomesafen residue 232 days after 0.25 and 0.50 kg ai ha-1 applications was detected to 20 cm depth with most fomesafen concentrated in 0 to 10 cm depth in a clay soil (Cobucci et al. 1997). Small fruit and vegetable production in
Florida is conducted on soils with typically high sand concentrations that would indicate fomesafen has potential to be mobile.
Water and solute movement within the soil bed is primarily influenced by localized, drip irrigation in the plasticulture system. Nutrients and pesticides applied through adequate drip
28 irrigation tend to be maintained in the root zone (Haynes 1990; Leib and Jarrett 2003). In Florida plasticulture fertigation, nitrogen leaching increases with rate and irrigation (Zotarelli et al.
2008). Nitrogen fertilizers and herbicides leach differently depending on adsorption with increased movement on previously wetted soils (Gerstl et al. 1981; Haynes 1990). In an irrigated soil, water moves horizontally first by capillarity and then vertically by gravity (Al-Quina and
Abu-Awwad 2001). Drip irrigation wetted zones from emitters first appear round to elongated or as volume increases (Simonne et al. 2003, 2006). Horizontal movement also occurs at the interface between soil layers or on top of an impermeable layer. Loamy soils usually have slow vertical infiltration rates, whereas in sandy soils lateral movement of water is restricted by the large amount of macropores (Heuvelman and McInnes 1997). There are a multitude of factors affecting water and solute movement and volume of the wetted zone in the soil including solute and soil characteristics, initial moisture content, irrigation flow rate, and plant water use
(Farneselli et al. 2008; Gerstl et al. 1981; Santos et al. 2003; Simonne et al. 2003, 2006).
Optimum small fruit and vegetable plasticulture drip irrigation management on a fine sand soil may be achieved by using drip tapes with a 20 to 30 cm emitter spacing and irrigations less than
900 L 100 m-1 (Farneselli et al. 2008; Simonne et al. 2006). Optimum fertigation is within 30 cm depth root zone of crop plant that prevents nutrient leaching with complete emitter to emitter coverage. Simonne et al. (2006) reported when a single drip tape is used as in strawberry production only 40% of the 0.7 m bed width was wetted at widest point of optimum applied volume. Increasing irrigation volume on fine sand increased the depth of the water front at rate of 0.15 mm L-1 100 m-1. Simonne et al. (2006) stated increasing volume only increased max width of bed wetted to 57% on Lakeland fine sand, compared to 70% reported by Santos et al.
(2003) on Eau Gallie fine sand. Simone et al. (2003) observed in Lakeland fine sand that 298 L
29 h-1 100 m-1 appeared round with a wetted area of 22 and 20 cm depth and width, respectively.
Shape was elongated at 596 L h-1 100 m-1 with a wetted area depth and width of 29 and 23 cm, respectively. Fomesafen is applied to the bed top and the drip irrigation is laid beneath the soil surface, so movement of water may not significantly affect fomesafen dissipation particularly towards the edge of the bed tops that are further away from drip line. Since fomesafen is now widely used in Florida plasticulture production it is imperative to understand fomesafen behavior, considering limited published data regarding its persistence and movement in the soil of the system.
Objective
Florida producers are currently transitioning into the post-methyl bromide era with the use of alternative soil fumigants. Reduced weed control has been associated with many of these alternative fumigants making supplementary measures necessary. Preemergence herbicide applications may complement fumigants and be a part of a new weed management program for growers. In Florida plasticulture, purple and yellow nutsedge are problematic perennial weeds that may compete with the crop, affect the ability to harvest, and reduce yield; all of which lower profit margins for producers. Fomesafen, a protoporphyrinogen oxidase inhibitor, is a potential preemergence herbicide for control of nutsedge and additional weeds in Florida plasticulture production. Previous field application of fomesafen has shown control to be erratic for nutsedge.
Comprehensive research is needed to evaluate fomesafen for potential use in production to improve our understanding of fomesafen behavior in raised bed plasticulture in Florida, provide information for development of strategies to maximize preemergence herbicide efficacy in the system, and ultimately may broaden fomesafen utility for producers throughout the state. The objectives of this research are to evaluate: (1) application timing influence on fomesafen
30 efficacy; (2) purple nutsedge tuber susceptibility to fomesafen; (3) fomesafen persistence and movement in Florida strawberry production system; (4) effect of fumigation on fomesafen persistence; (5) effect of plastic mulch on fomesafen dissipation (6) incorporation of fomesafen for purple and yellow nutsedge control.
31 Figure 1-1. Purple and yellow nutsedge inflorescences (Boyd 2013). A) Purple nutsedge (Cyperus rotundus L.). B) Yellow nutsedge (Cyperus esculentus L.).
32 Figure 1-2. Fomesafen chemical structure (Shaner 2014).
33 Figure 1-3. An example of Protox inhibition in susceptible plants.
34 CHAPTER 2 APPLICATION TIMING INFLUENCES PURPLE AND YELLOW NUTSEDGE SUSCEPTIBILITY TO EPTC AND FOMESAFEN
Introduction
Purple (Cyperus rotundus L.) and yellow (C. esculentus L.) nutsedge are problematic weeds in Florida plasticulture production that can compete with the desired crop plant for light and nutrients. Motis et al. (2003) reported 10% pepper (Capsicum annuum L.) yield loss with fewer than five yellow nutsedge tubers planted m-2 compared to weed-free control. Full interference by purple and yellow nutsedge reduced tomato (Solanum lycopersicum L.) shoot dry weight 34% and 28%, respectively (Morales-Payan et al. 2003). Purple nutsedge densities of 126 plants m-2 at 10 weeks after transplant resulted in 53% and 50% tomato fruit number and weight reductions, respectively, compared to fumigant treatments with less than 15 plants m-2 (Gilreath and Santos 2004). Season-long purple and yellow nutsedge competition can reduce pepper yield greater than 70% (Morales-Payan et al. 1998; Motis et al. 2004). Nutsedge density and competition timing affect the competitive relationship between nutsedge and horticultural crops
(Motis et al. 2003, Morales-Payan et al. 2003).
Historically, fruit and vegetable growers in Florida have relied on methyl bromide as the foundation for weed, nematode, and soilborne pathogen management (Chandler et al. 2001;
Noling and Becker 1994). However, methyl bromide was classified as an ozone depleting substance under the provisions of the Montreal Protocol and its use is now prohibited in all fruit and vegetable crops in Florida. Many alternative fumigants have been registered that control or suppress nutsedge (McAvoy and Freeman 2013a, 2013b). However, alternative fumigants are not as effective on nutsedge as methyl bromide. Gilreath and Santos (2005) noted a five to seven fold greater purple nutsedge density in plots not treated with methyl bromide compared to where methyl bromide was applied. Florida growers have reported an increase in nutsedge density
35 following the loss of methyl bromide and poor or inconsistent nutsedge control with alternative fumigants (Snodgrass et al. 2011). These observations were supported by a trial conducted by
Jacoby (2012) at the University of Florida that evaluated alternative fumigants and found that nutsedge density increased over three years in all treatments suggesting that supplementary measures such as the use of preemergence herbicides are necessary to effectively control nutsedge.
Several preemergence herbicides with activity on nutsedge including EPTC and fomesafen have been registered for use in tomato production in Florida and have potential for use in other high value crops such as strawberry (Fragaria × ananassa), but have not been widely adopted because of inconsistent efficacy and concern over crop tolerance. EPTC is a thiocarbamate herbicide that inhibits cuticle formation at the early stages of germination with most susceptible plants failing to emerge (Fuerst 1987; Shaner 2014). EPTC can suppress growth and delay emergence of both purple and yellow nutsedge. For example, EPTC at 4.48 kg ai ha-1 reduced purple nutsedge tuber sprouting 44% 2 weeks after treatment (WAT) (Holt et al. 1962).
EPTC at 3.36 kg ai ha-1 reduced yellow nutsedge tuber production 66% and shoot weight 29% from nontreated control 12 WAT (Keeley and Thullen 1974).
Fomesafen is a diphenylether herbicide that inhibits the protoporphyrinogen oxidase enzyme (Protox) that catalyzes the conversion of protoporphyrinogen IX to protoporphyrin IX as part of the tetrapyrrole biosynthesis pathway (Duke et al. 1991; Scalla and Matringe 1994).
Protox inhibitors cause a rapid build up of substrates that when in the presence of light, lead to lipid peroxidation resulting in cell death (Becerril and Duke 1989; Scalla and Matringe 1994).
Leaf chlorosis, necrosis, and desiccation are symptoms of plants susceptible to fomesafen
(Shaner 2014). Fomesafen applied preemergence can suppress or control yellow nutsedge
36 growth. In open field cotton production, soil-applied herbicide programs containing fomesafen controlled yellow nutsedge greater than 90% (Wilcut et al. 1997). In plasticulture production, drip applied fomesafen at 0.28 kg ai ha-1 reduced yellow nutsedge punctures of mulch 89%, 56 days after treatment (DAT) (Monday et al. 2015). Variable fomesafen efficacy on purple nutsedge has been demonstrated by previous research. Miller and Dittmar (2014) found that preemergence applications of fomesafen at 0.42 kg ai ha-1 controlled 48 to 50% of purple and yellow nutsedge mix 28 DAT, with 52% nutsedge control at 11 WAT. Boyd (2015) reported fomesafen application alone did not reduce purple nutsedge populations, but a fomesafen plus S- metolachlor tank-mix reduced purple nutsedge counts by 84% in one year.
Preemergence herbicides used in combination with alternative fumigants may facilitate season-long weed control in plasticulture production. However, it is important to note that field preparation can break up tuber dormancy and stimulate nutsedge growth (Alves et al. 2013;
Taylorson 1967). The time frame from soil preparation to fumigation and herbicide application may affect nutsedge growth and subsequently herbicide efficacy. Understanding the interaction between nutsedge growth and herbicide activity is essential to optimize efficacy. The objective of this study was to investigate the influence of application timing on efficacy of EPTC and fomesafen for purple and yellow nutsedge control.
Material and Methods
Purple Nutsedge
Two greenhouse experiments were conducted at the University of Florida in Gainesville,
FL (29.64°N, 82.36°W), from May to August 2014, to investigate purple nutsedge (Cyperus rotundus L.) tuber growth stage susceptibility to EPTC and fomesafen applications. Purple nutsedge tubers and field soil were gathered at the University of Florida Plant Science Research
37 and Education Unit, Citra, FL (29.40°N, 82.18°W). Five non-sprouted purple nutsedge tubers selected for similar size per replication were planted in field soil (Hague series sand; loamy, siliceous, semiactive, hyperthermic Arenic Hapludalfs) with 1.4% organic matter and a pH of
5.8. Tubers were planted at a depth of 2.5 to 5.0 cm in plastic pots with 110.3 cm2 surface area x
12.0 cm depth in a temperature controlled greenhouse set for 32/25 °C (day/night) temperature.
Experimental design was a randomized complete block with 10 blocks. Treatments included EPTC (Eptam 7E Selective Herbicide, Gowan Company, Yuma, AZ) at 2.91 kg ai ha-1 and fomesafen (Reflex 2L Liquid Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 kg ai ha-1 at six different timings, plus a nontreated check. Application timings were spread three days apart and were 0, 3, 6, 9, 12, and 15 days after planting (DAP). The rates for
EPTC and fomesafen are currently labeled for use in Florida tomato production. Treatments were applied within a spray chamber (Generation III Research Sprayer, DeVries Manufacturing,
Hollandale, MN) calibrated to deliver 187 L ha-1. Herbicides were incorporated with 1.3 cm rainfall equivalent with overhead irrigation over 0.5 hours. Pots were visually monitored and watered as needed to prevent soil moisture deficiencies.
Yellow Nutsedge
Two greenhouse experiments were conducted at the University of Florida Gulf Coast
Research and Education Center (GCREC) in Balm, FL (27.76°N, 82.23°W), from March to May
2015, to investigate yellow nutsedge (Cyperus esculentus L.) tuber growth stage susceptibility to
EPTC and fomesafen applications. Five non-sprouted yellow nutsedge tubers (JB Natural Foods
S.L., Puzol, Valencia, Spain) selected for similar size per replication were planted in field soil
(Myakka series fine sand; sandy, siliceous, hyperthermic Aeric Alaquods) with 0.8% organic matter and a pH of 7.6 gathered at GCREC. Tubers were planted at a depth of 2.5 to 5.0 cm in
38 110.3 cm2 surface area x 9.0 cm depth plastic pots in a greenhouse that averaged approximately
27/20 °C (day/night) temperature across experiments as monitored by HOBO Pro v2 data logger
(Onset Computer Corporation, Bourne, MA).
Experimental design was a randomized complete block with five blocks. Treatments were the same for the yellow nutsedge experiment as previously stated in purple nutsedge experiment.
However, herbicides were applied with a CO2-pressured backpack sprayer calibrated to deliver
187 L ha-1 with a single DG 9502 EVS flat-fan nozzle (TeeJet, Spraying Systems Co., Wheaton,
IL). Herbicides were incorporated with 1.3 cm rainfall equivalent with overhead irrigation over
0.5 hours and pots were watered as needed, throughout the experiment.
Data Collection
At each application, 10 and 5 additional nontreated pots with five tubers each were harvested for purple and yellow nutsedge, respectively. Sprouted shoot number and shoot length from tuber data was taken to indicate nutsedge above and below soil surface development at time of application. Rhizomes elongated from tuber to any subsequent growth stage are defined as shoots in the experiments. Shoot length includes rhizomatous growth from tuber to the tallest leaf tip.
For all treatments emergence, shoot height, leaf number and injury was evaluated at 4 weeks after planting (WAP). Shoot height was measured from the soil surface to tip of tallest leaf of each shoot. Injury was evaluated on a 0 to 100 percent scale where 0 equals no visible chlorosis or stunting and 100 equals no emergence or complete necrosis. For each pot, tubers and plant shoots at the soil surface were harvested at 4 WAP. All tuber and plant shoots were then oven-dried at 60 °C for 48 hours for purple nutsedge and at 40 °C for 72 hours for yellow
39 nutsedge to determine dry weights. Tubers harvested at application timings were also dried and weighed using the same methodology for each species.
Statistical Analysis
Data were subjected to ANOVA at the 0.05 probability level in SAS (SAS® Institute v.
9.4, Cary, NC) using the mixed procedure with block as the random factor. Data were checked for normality and constant variance prior to analysis. Purple and yellow nutsedge were analyzed separately as trials for each species were conducted at different locations and timings. Means were compared using the least squares means statement with the Tukey adjustment and orthogonal contrasts were performed to compare nontreated to each herbicide and herbicides to one another. In all analyses, significance was determined at the p≤0.05 level. Experiment by treatment interactions were not detected and, thus, experiments were combined for each species.
Results and Discussion
Purple Nutsedge
Purple nutsedge shoot number and length increased with application time from day of planting (Table 2-1). Applications at 0 to 3 DAP had half or fewer shoots than later timings.
Shoot number did not significantly increase after 6 DAP. Shoot length increased approximately four-fold from 3 DAP to 12 DAP. Tubers harvested at applications were similar and weighed
1.59±0.04 g across all timings. Temperatures were in an appropriate range for tuber sprouting with diurnally alternating temperatures from 32 to 27 °C (Miles et al. 1996; Nishimoto 2001).
However, 3 sprouted shoots per five tubers by 15 DAP is less than the 92% maximum sprouting reported by Wallace et al. (2013) under similar conditions from tubers collected in Georgia.
Weed growth stage and density can affect herbicide efficacy, and the lack of purple nutsedge
40 growth due to greater tuber dormancy may have led to increased short-term EPTC and fomesafen activity compared to previous studies (Lati et al. 2012; Pires da Silva et al. 2014; Wang 2002).
Orthogonal contrasts indicate EPTC and fomesafen applications averaged across all timings decreased purple nutsedge emergence, shoot height, leaf number, and dry shoot mass compared to the nontreated control (Table 2-2). The two herbicides similarly affected purple nutsedge emergence and caused comparable injury. EPTC applications appear to decrease average shoot height, leaf number, and dry shoot mass to a greater extent than fomesafen treatments. Short-term suppression of purple nutsedge by EPTC and fomesafen has been previously observed (Holt et al. 1962; Miller and Dittmar 2014). However, Boyd (2015) reported
EPTC at 2.29 kg ai ha-1 and fomesafen at 0.42 kg ai ha-1 applications had no effect on season- long purple nutsedge density compared to nontreated control in tomato production.
EPTC and fomesafen applications made on the day of planting reduced emergence, shoot height, leaf number and shoot mass at least 67%, 48%, 20%, and 79%, respectively, from the nontreated control at 4 WAP, and caused greater than 70% injury. EPTC treatments made 9 DAP or earlier reduced both average shoot height and leaf number compared to the nontreated control, whereas only fomesafen applications at 3 DAP or earlier had a reduction. All applications except fomesafen at 15 DAP reduced shoot biomass. Purple nutsedge emergence, shoot height, leaf number, and shoot mass tended to increase with herbicide application time from day of planting and injury tended to decrease, although the differences were not always significant at 4 WAP.
The more time allowed for nutsedge growth to time of application can significantly affect efficacy. EPTC and fomesafen treatments at 0 DAP had greater than 70% dry shoot mass reduction compared to equivalent treatments made at 15 DAP. However, tuber dry weights per pot were similar and averaged 1.49±0.03 g across all treatments.
41 EPTC and fomesafen are most effective on purple nutsedge when applied at early sprouting. Previous research has demonstrated early purple nutsedge sprouting to be susceptible to herbicide application (Wang 2002). Fishler et al. (1995) reported purple nutsedge was sensitive to benfuresate incorporated in soil up to eight days after initiation of tuber sprouting, whereas older shoots recovered from herbicide injury. Practices that enhance EPTC and fomesafen contact with purple nutsedge during early shoot growth may increase herbicide activity and improve consistency.
Yellow Nutsedge
Yellow nutsedge shoot number increased with application time from day of planting
(Table 2-1). Yellow nutsedge growth appears to accelerate considerably from 1 to 2 WAP with shoot number quadrupling from 6 to 15 DAP. Average shoot length was similar across all application timings. Tubers harvested at applications had similar weights averaging 2.12±0.05 g across all timings.
Herbicide applications across all timings reduced yellow nutsedge growth compared to the nontreated (Table 2-3). EPTC and fomesafen comparably affected yellow nutsedge emergence, shoot height, leaf number, shoot mass, and caused similar injury. EPTC and fomesafen have demonstrated short-term control of yellow nutsedge. Keeley and Thullen (1974) reported applications of EPTC at 3.36 kg ai ha-1 on the day of planting reduced nutsedge emergence 93% at 4 WAT and fresh shoot mass 97% at 6 WAT. Grichar (1992) reported 99% control of yellow nutsedge in open field peanut (Arachis hypogaea) production at 20 days after application of fomesafen at 0.43 kg ai ha-1. Monday et al. (2015) observed fomesafen at 0.28 kg ai ha-1 reduce yellow nutsedge punctures in plastic mulch 80% at 28 DAT.
42 EPTC and fomesafen efficacy on yellow nutsedge appears to increase with applications made within the first week of planting. Herbicide applications made 6 DAP or earlier reduced emergence and shoot mass at least 57% and 82%, respectively, from the nontreated, and caused greater than 65% injury. Fomesafen application made 0 DAP was the only treatment to reduce average shoot height and leaf number from the nontreated. Harvested tubers at 4 WAP had similar fresh and dry weights to nontreated across all timings. Each pot of five tubers had similar dry weights of 1.98±0.03 g across all treatments. At 4 WAP, yellow nutsedge emergence, shoot height, leaf number, and shoot mass tended to increase with application time from day of planting and injury tended to decrease, although the differences were not always significant.
EPTC treatments at 0 and 3 DAP had less than half as much emergence and more than five times the amount of injury than corresponding treatment at 15 DAP. Fomesafen applications made 6
DAP or earlier had at least a 50% and 78% reduction in emergence and shoot mass, respectively, than fomesafen treatment made 15 DAP. Nutsedge tolerance to EPTC and fomesafen increases with plant age. It has been documented that thiocarbamate and diphenylether herbicides most effectively suppress yellow nutsedge when applied during early growth stages and are capable of reducing tuber and shoot production; however there is no evidence of the herbicides terminating tubers (Felix and Newberry 2012; Keeley and Thullen 1974; Pereira and Crabtree 1986; Pereira et al. 1987). Applying EPTC and fomesafen when the herbicides can effectively control yellow nutsedge is critical for successful long-term suppression.
Early applications of EPTC and fomesafen have demonstrated the ability to suppress short-term purple and yellow nutsedge growth. The results suggest that increased efficacy will occur when herbicides are applied as closely to tuber sprouting as possible. The herbicides appear to have potential as part of a weed management program for growers to complement
43 fumigants for preemergence nutsedge control. Further research on efficacy of these herbicides with greater nutsedge pressure and length of experimentation in plasticulture setting is necessary before recommending EPTC and fomesafen for purple and yellow nutsedge suppression.
44 Table 2-1. Purple and yellow nutsedge shoot number per pot and average shoot length when herbicides were applied in two combined greenhouse experiments for purple and yellow nutsedge, Gainesville, FL in 2014 and Balm, FL in 2015, respectively. Purple nutsedge Yellow nutsedge Application timing (DAPa) Shoots Shoot length Shoots Shoot length # pot-1 cm shoot-1 # pot-1 cm shoot-1 0b 3 1 ac 1.8 a 1 a 0.3 6 2 b 4.4 ab 1 ab 1.5 9 2 b 5.0 ab 2 ab 1.9 12 2 b 7.1 b 3 bc 2.9 15 3 b 11.3 c 4 c 7.5 p-value <0.0001 <0.0001 <0.0001 0.1453 aDAP = days after planting. bApplication at 0 DAP had zero shoots and was excluded from the model due to variance of zero for shoot number and shoot length conflicting with model assumption of constant variance. cMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
45 Table 2-2. Purple nutsedge average emergence per pot, shoot height, leaf number, dry shoot mass per pot, and injury four weeks after planting from EPTC and fomesafen applications at six timings in two combined greenhouse experiments, 2014, Gainesville, FL. Purple nutsedge (4 WAPa) Herbicideb Application (DAPc) Emergence Shoot height Leaf number Shoot mass Injury # pot-1 cm shoot-1 # shoot-1 g pot-1 - % - Nontreated control 3 ad 19.8 a 5 a 0.077 a EPTC 0 0 d 6.5 cd 3 c 0.004 e 94 a 3 1 cd 5.7 d 3 c 0.008 de 77 ab 6 2 abc 6.3 cd 3 c 0.012 de 63 abc 9 2 abc 10.2 bcd 4 bc 0.017 cde 37 cde 12 2 abc 10.7 abc 4 bc 0.029 cde 24 de 15 2 abc 13.9 ab 4 abc 0.034 bcd 14 e Fomesafen 0 1 bcd 10.3 bcd 4 bc 0.016 cde 74 ab 3 2 abc 10.3 bcd 4 bc 0.020 cde 57 bc 6 2 abc 12.2 ab 4 abc 0.020 cde 49 bcd 9 2 abc 13.1 ab 5 ab 0.044 bc 37 cde 12 2 abc 12.7 ab 5 a 0.033 bcde 34 cde 15 2 ab 13.3 ab 5 a 0.058 ab 18 de Contrasts EPTC vs. Fomesafene 0.4059 0.0028 <0.0001 <0.0001 0.1078 Nontreated control vs. EPTCf 0.0070 <0.0001 <0.0001 <0.0001 Nontreated control vs. Fomesafeng 0.0238 0.0365 0.0128 <0.0001 aWAP = weeks after planting. bProducts applied were Eptam 7E Selective Herbicide (EPTC), Gowan Company, Yuma, AZ at 2.94 kg ai ha-1 and Reflex 2L Liquid Herbicide (fomesafen), Syngenta Crop Protection, LLC, Greensboro, NC at 0.42 kg ai ha-1. cDAP = days after planting. dMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
46 eThis contrast compares the mean of all treatments with EPTC vs. the mean of all treatments with fomesafen. fThis contrast compares the nontreated control vs. the mean of all treatments with EPTC. gThis contrast compares the nontreated control vs. the mean of all treatments with fomesafen.
47 Table 2-3. Yellow nutsedge average emergence per pot, shoot height, leaf number, dry shoot mass per pot, and injury four weeks after planting from EPTC and fomesafen applications at six timings in two combined greenhouse experiments, 2015, Balm, FL. Yellow nutsedge (4 WAPa) Herbicideb Application (DAPc) Emergence Shoot height Leaf number Shoot mass Injury # pot-1 cm shoot-1 # shoot-1 g pot-1 - % - Nontreated control 7 ad 16.6 a 6 a 0.57 a EPTC 0 1 d 8.3 ab 4 ab 0.04 c 80 ab 3 2 cd 8.3 ab 5 ab 0.05 c 74 ab 6 2 bcd 9.0 ab 4 ab 0.05 c 72 ab 9 4 abcd 9.4 ab 4 ab 0.15 bc 51 abcd 12 5 abc 10.7 ab 5 a 0.17 bc 49 abcd 15 5 ab 15.9 ab 5 a 0.31 abc 14 cd Fomesafen 0 1 d 7.1 b 3 b 0.03 c 88 a 3 2 bcd 7.0 b 4 ab 0.05 c 77 ab 6 3 bcd 9.2 ab 5 ab 0.10 c 66 ab 9 5 abcd 11.3 ab 5 ab 0.12 c 54 abc 12 5 ab 11.0 ab 5 a 0.24 abc 43 bcd 15 6 a 12.1 ab 5 a 0.47 ab 13 d Contrasts EPTC vs. Fomesafene 0.1139 0.5510 0.6010 0.3240 0.9596 Nontreated control vs. EPTCf <0.0001 0.0007 0.0098 <0.0001 Nontreated control vs. Fomesafeng 0.0013 0.0002 0.0035 <0.0001 aWAP = weeks after planting. bProducts applied were Eptam 7E Selective Herbicide (EPTC), Gowan Company, Yuma, AZ at 2.94 kg ai ha-1 and Reflex 2L Liquid Herbicide (fomesafen), Syngenta Crop Protection, LLC, Greensboro, NC at 0.42 kg ai ha-1. cDAP = days after planting. dMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons. eThis contrast compares the mean of all treatments with EPTC vs. the mean of all treatments with fomesafen.
48 fThis contrast compares the nontreated control vs. the mean of all treatments with EPTC. gThis contrast compares the nontreated control vs. the mean of all treatments with fomesafen.
49 CHAPTER 3 EVALUATION OF FOMESAFEN DOSE RESPONSE ON PURPLE NUTSEDGE TUBERS
Introduction
Purple nutsedge (Cyperus rotundus L.) is a problematic perennial weed in plasticulture that can pierce mulch and compete with vegetable crops. A single sprouted purple nutsedge tuber under mulch can give rise to a 16.1 m2 patch with 1,550 shoots within 32 weeks of planting
(Webster 2005b). Purple nutsedge tubers present in the soil may remain dormant until receiving the appropriate stimuli, which tends to be temperature in temperate climates and moisture in arid climates (Forcella et al. 2000). When purple nutsedge tubers sprout they produce one or multiple determinate rhizomes that grow upwards and form a basal bulb just beneath the soil surface.
Each basal bulb gives rise to shoots, fibrous roots, and indeterminate rhizomes which may give rise to secondary basal bulbs, tubers, or additional shoots (Wills 1987). The majority of roots tend to grow from the tuber in purple nutsedge (Obrigawitch 1980). Shoots emerge, grow, and flower within seven to eight weeks of emergence with tuber formation beginning four to six weeks after emergence (Hauser 1962; Stoller and Sweet 1987; Wills et al. 1980). Season long interference from purple nutsedge at a density of 200 shoots m-2 reduced fruit yield of bell pepper (Capsicum annuum L.) by 32% and tomato (Solanum lycopersicum L.) by 44% (Morales-
Payan et al. 1997).
Effective control of purple nutsedge in Florida involves inhibiting the production of new tubers and reducing tuber viability. Preemergence herbicides such as fomesafen applied under plastic mulch in combination with fumigation may decrease purple nutsedge populations by diminishing in-season propagation. Fomesafen is a diphenylether herbicide that inhibits protoporphyrinogen oxidase (Protox). Protox catalyzes the conversion of protoporphyrinogen IX
(Protogen IX) to protoporphyrin IX (Proto IX) as part of the tetrapyrrole biosynthesis pathway
50 (Duke et al. 1991; Scalla and Matringe 1994). The herbicidal effects of Protox inhibitors are relatively quick in susceptible species due to fast build up of substrates rather than from the depletion of tetrapyrroles such as chlorophyll (Becerril and Duke 1989). It is believed that as
Protogen IX accumulates above normal levels, it diffuses out of the site of synthesis, and is oxidized nonenzymatically to Proto IX that is then no longer available for magnesium insertion from magnesium chelatase to continue the tetrapyrrole biosynthesis pathway (Matringe et al.
1989). Proto IX in the presence of light and molecular oxygen generates high levels of singlet oxygen as an initiating factor for lipid peroxidation of polyunsaturated fatty acids in the membranes resulting in cell death (Scalla and Matringe 1994;Witkowski and Halling 1989).
Symptomology of susceptible plants to fomesafen includes leaf chlorosis, necrosis, and desiccation (Shaner 2014). Uniform coverage of the target site is critical for weed control with
Protox inhibiting herbicides and direct contact with emerging weeds is necessary for control in preemergence applications. Fomesafen is rapidly absorbed by leaf tissue within one hour from a postemergence application, and may also be absorbed by the root system where it is primarily xylem mobile (Shaner 2014).
Fomesafen is registered in pepper and tomato production in Florida and has potential for use in other high value crops, but has not been widely adopted because of inconsistent efficacy and concern over crop tolerance. Fomesafen can control or suppress yellow nutsedge (Cyperus esculentus L.) growth. Monday et al. (2015) observed an 89% reduction in yellow nutsedge punctures of mulch with drip applied fomesafen at 0.28 kg ai ha-1 at 8 weeks after treatment
(WAT). Soil-applied herbicide programs containing fomesafen controlled yellow nutsedge greater than 90% in open field cotton production (Wilcut et al. 1997). However, fomesafen has unreliable efficacy on purple nutsedge. Miller and Dittmar (2014) reported preemergence
51 applications of fomesafen at 0.42 kg ai ha-1 suppressed a mix of purple and yellow nutsedge by
52% at 11 WAT. The study does not specify which species was controlled and it is possible the reduction was primarily due to yellow nutsedge susceptibility. Fomesafen application alone did not reduce purple nutsedge populations in Florida tomato and strawberry production (Boyd 2015;
Boyd and Reed 2016).
Preemergence treatments applied under plastic mulch with adequate efficacy on purple nutsedge are desirable because they enable rotation of active ingredients to avoid herbicide resistance and prevent puncture of the plastic mulch facilitating its use with multiple crops.
Herbicide options that can be used in conjunction with fumigation are needed to reduce nutsedge populations over time, especially if tubers are damaged or tuber production is inhibited. The objective of this research was to evaluate purple nutsedge tuber susceptibility to multiple concentrations of fomesafen at different growth stages, exposure lengths, and in the presence of light.
Material and Methods
Growth chamber experiments were conducted at the University of Florida Gulf Coast
Research and Education Center (GCREC) in Balm, FL (27.76°N, 82.23°W) in 2016, to investigate purple nutsedge tuber susceptibility to fomesafen. For all experiments, purple nutsedge tubers were gathered at GCREC, selected for similar size per replication, and 25 tubers were placed in each 95 × 15 mm polystyrene Petri dish (Thermo Fisher Scientific, Waltham,
MA). All petri dishes were placed in a 35/25 °C temperature growth chamber (Model I-30BLL,
Percival Scientific, Inc., Perry, IA) with temperatures alternating every 12 hours for duration of experiments. For all studies, tubers were immersed approximately halfway in 20 mL of fomesafen treatment solution. Fomesafen is labeled for use in Florida pepper and tomato
52 production at 0.28 to 0.42 kg ai ha-1. Fomesafen applied at 0.28 kg ai ha-1 had initial concentrations in soil at 0 to 8 cm depth of approximately 175 ppb (parts per billion) (Li 2014;
Mueller et al. 2014).
First Experiment
The experiment was conducted in darkness and treatments included sodium salt of fomesafen (Reflex 2L Liquid Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0,
2.17×10-8, 2.17×10-7, 2.17×10-6, and 2.17×10-5 M corresponding to 0, 10, 100, 1000, and 10000 ppb, respectively, exposed to dry purple nutsedge tubers or tubers that were imbibed for 96 hours in water. Tubers were exposed to fomesafen treatment solution for 96 hours. Experimental design was a factorial with four replications.
Second Experiment
Purple nutsedge tubers were exposed to fomesafen at five previously mentioned concentrations for seven days in darkness. Experimental design was a randomized complete block with four replications.
Third Experiment
Treatments included sodium salt of fomesafen at 0, 2.17×10-7, 1.09×10-6, 2.17×10-6, and
2.17×10-5 M corresponding to 0, 100, 500, 1000, and 10000 ppb, respectively, exposed to dry tubers for 96 hours in darkness and then 96 hours in light measured at 75 μmol m-2 s-1 photosynthetic photon flux density (PPFD) with quantum sensor (LI-190, LI-COR, Inc., Lincoln,
NE) and light sensor logger (LI-1500, LI-COR, Inc., Lincoln, NE). Experimental design was a randomized complete block with four replications.
Data Collection and Analysis
53 For all studies, the number of tubers sprouted was counted before and after fomesafen exposure. For each petri dish, sprouted growth from tuber was harvested at completion of experimental period in all studies. Growth was then oven-dried at 40 °C for 96 hours to determine dry weights. Tubers were dissected longitudinally and tested for viability using triphenyl tetrazolium chloride test (Akin and Shaw 2001; Miles et al. 1996). Dissected tubers were exposed to 0.1% triphenyl tetrazolium solution at 25 °C for three hours. Tuber weights were measured prior to imbibing or exposure to fomesafen and following exposure to fomesafen by petri dish in the first and second experiments. Injury was evaluated on a 0 to 100 percent scale where 0 equals no visible chlorosis or stunting and 100 equals complete necrosis in the third experiment after 96 hours of light exposure.
Data were subjected to ANOVA at the 0.05 probability level in SAS (SAS® Institute v.
9.4, Cary, NC) using the mixed procedure. Data were checked for normality and constant variance prior to analysis. Means were compared using the least squares means statement with the Tukey adjustment at p=0.05. All experiments were repeated. Experiment by treatment interactions were not detected and experiments were combined for all studies.
Results and Discussion
First Experiment
Purple nutsedge tubers before imbibing or treatment exposure had similar weights across treatments (P=0.8194) averaging 13.79±0.19 g. Imbibed tubers had similar sprouting in all dishes
(P=0.2189) with 15±1 sprouted tubers per dish prior to exposure of treatments. Imbibing tubers affected the number of tubers sprouted and dry sprouted growth biomass after exposure to fomesafen (Table 3-1). Dry sprouted growth biomass for imbibed treatments was four times greater than dry tuber treatments. However, fomesafen concentration did not have an affect on
54 tuber growth or viability. Tubers after treatment exposure had similar weight across treatments
(P=0.5731) averaging 15.84±0.23 g.
Greater than 60% of tubers sprouted by the end of the experiment with approximately
70% of the tubers in the experiment still viable. Nontreated control viability was similar to previous research conducted by Akin and Shaw (2001) that observed 73% purple nutsedge viability in tubers from the field. Tubers were exposed to optimal temperature and temperature fluctuations to promote sprouting and resulted in 90% of viable tubers sprouting (Miles et al.
1996; Nishimoto 2001).
Second Experiment
Purple nutsedge tubers before treatment exposure had similar weights across treatments
(P=0.1734) averaging 12.67±0.34 g. Fomesafen concentration did not have an affect on tuber sprouting (P=0.3005), dry sprouted growth biomass (P=0.4014), and viability (P=0.4041), (data not shown). Across treatments on average 15±1 tubers sprouted with 0.22±0.02 g sprouted growth biomass, and 18±1 tubers were viable per dish. Tubers after treatment exposure had similar weight across treatments (P=0.1738) averaging 14.68±0.39 g.
Previous research indicates fomesafen has potential to affect nutsedge tuber viability.
Preemergence and preplant-incorporated treatments of fomesafen at 0.28 kg ai ha-1 reduced the number of yellow nutsedge viable tubers greater than 90% in a potted experiment (Wilcut et al.
1991). Applications of another Protox inhibitor, sulfentrazone, reduced both purple and yellow nutsedge tuber viability in prior research (Akin and Shaw 2001; Pires da Silva et al. 2014).
However, fomesafen did not affect purple nutsedge tuber growth or viability in the growth stage or dose response experiment. This is consistent with field research that suggests fomesafen efficacy on purple nutsedge is deficient (Boyd 2015; Boyd and Reed 2016).
55 Third Experiment
Fomesafen concentration did not have an affect on tuber sprouting and viability (Table 3-
2). Greater than 80% of viable tubers sprouted by the end of the experiment with approximately
60% of the tubers in the experiment still viable. Only the fomesafen treatment at 2.17×10-5 M concentration caused significant visual injury and reduced dry sprouted growth greater than 70% compared with the nontreated control. Fomesafen at the highest concentration affected purple nutsedge growth under light conditions of less than 5% of typical full sun PPFD. It is possible under greater PPFD levels increased damage may have been observed under lower fomesafen concentrations.
Light may be necessary for fomesafen to be an effective weed control measure for purple nutsedge. However, the plasticulture system limits light exposure to fomesafen treated nutsedge until it penetrates the mulch. Fomesafen applications may reduce purple nutsedge propagation during the growing season by controlling contacted shoots even if there is limited fomesafen translocation from purple nutsedge growth and tubers do not effectively absorb the herbicide directly.
Even at high concentrations fomesafen exposure for seven or less days had no affect on purple nutsedge tuber growth or viability without light exposure. In the third experiment fomesafen concentration did not affect tuber sprouting or viability, and only the 2.17×10-5 M concentration treatment reduced dry sprouted growth biomass and caused significant visually injury. Potentially purple nutsedge tubers do not effectively absorb fomesafen directly and there is limited translocation from purple nutsedge growth, or tubers absorb fomesafen, but there is no effect due to absence of tetrapyrrole synthesis in tuber. Light may be necessary for fomesafen to be an effective weed control measure for purple nutsedge although it is limited in field situations
56 until shoots puncture the plastic mulch and rates registered for use in vegetables are unlikely to be effective.
57 Table 3-1. Purple nutsedge tuber sprouting, tuber viability, and dry sprouted growth biomass after exposure to fomesafen with or without tuber imbibition in two combined growth chamber experiments, 2016, Balm, FL. Imbibitiona Sprouting Viability Dry mass # # g Pre-treatment 16 ab 18 0.29 a None 15 b 17 0.07 b Concentrationc (Md) 0.00 17 18 0.20 2.17×10-8 15 17 0.16 2.17×10-7 15 17 0.16 2.17×10-6 15 17 0.19 2.17×10-5 16 18 0.20 Imbibition 0.0216e 0.1166 <0.0001 Concentration 0.5065 0.6352 0.2592 Imbibition*concentration 0.2478 0.7605 0.6330 Data presented by dish that contained 25 tubers. aTubers were imbibed for 96 (pre-treatment) and 0 (none) hours before treatment exposure. The number of sprouted tubers after imbibing averaged 15±1 before treatment exposure. bMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons. cFomesafen concentrations correspond to 0, 10, 100, 1000, and 10000 parts per billion of fomesafen sodium salt. dM = molarity. ep-values.
58 Table 3-2. Purple nutsedge tuber sprouting, tuber viability, injury, and dry sprouted growth mass after exposure to fomesafen concentrations and light in two combined growth chamber experiments, 2016, Balm, FL. Concentrationa Sprouting Viability Injury Dry mass Mb # # % g (ppb) 0.00 13 15 0 ac 0.37 a 2.17×10-7 13 16 0 a 0.41 a 1.09×10-6 13 15 1 a 0.45 a 2.17×10-6 12 15 4 a 0.40 a 2.17×10-5 11 14 64 b 0.10 b p-value 0.4794 0.5084 <0.0001 0.0100 Data presented by dish that contained 25 tubers. aFomesafen concentrations correspond to 0, 100, 500, 1000, and 10000 parts per billion of fomesafen sodium salt. bM = molarity. cMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
59 CHAPTER 4 PERSISTENCE AND MOVEMENT OF FOMESAFEN IN FLORIDA STRAWBERRY PRODUCTION
Introduction
In Florida small fruit and vegetable production preemergence herbicide treatments applied under plastic mulch with efficacy on a broad spectrum of weeds are desirable because they reduce the need for in-season weed control measures. Fomesafen, a diphenylether herbicide, inhibits the protoporphyrinogen oxidase (Protox) enzyme that catalyzes the conversion of protoporphyrinogen IX to protoporphyrin IX as part of the tetrapyrrole biosynthesis pathway
(Duke et al. 1991; Scalla and Matringe 1994). Tetrapyrroles, such as heme and chlorophyll, serve as cofactors in numerous essential enzymatic and signaling processes in plants including light harvesting, nitrogen fixation, oxygen transport, quenching of free radicals, respiration or phosphorylation, and storage (Beale and Weinstein 1990; Grimm 1999). Due to the rapid expansion of herbicide resistant weeds in the southern United States to other herbicide mechanisms of action, fomesafen preemergence applications have become an essential component of annual broadleaf weed control in agronomic crops (Shaner 2014; Sosnoskie et al.
2009). Fomesafen has the potential to be used as an alternative mechanism for of action for broadleaf and nutsedge (Cyperus spp.) control in Florida plasticulture production (Miller and
Dittmar 2014; Monday et al. 2015). However, fomesafen may persist at a high concentration in the production system for the entire growing season. This may dissuade producers from using the herbicide to avoid limitations on crop rotations for fear of injury.
Fomesafen can degrade rapidly under anaerobic, low redox potential, and sunlight conditions (Shaner 2014). Li (2014) reported lab incubated fomesafen had minimal degradation by soil microorganisms and biological degradation is unlikely to be a major pathway for
60 fomesafen dissipation under aerobic conditions in the field. Fomesafen open-field half-life varies under different soil conditions. Fomesafen half-life was reported from 28 to 66 days, after 0.18 kg ai ha-1 alone or 0.09 followed by 0.18 kg ai ha-1 applications with residue still detectable 350 days after treatment in a Madalin silty clay loam (Rauch et al. 2007). Mueller et al. (2014) reported fomesafen half-life over three experimental years on a loam soil averaged 46 days. Li
(2014) reported the half-life of fomesafen applied at 0.28 and 0.56 kg ai ha-1 was 6 and 4 days, respectively, for Cecil Tifton loamy sand, and was not detectable past 28 days.
Soil properties are important factors that determine a particular pesticide persistence and bioavailability. Fomesafen is a weak acid with increased sorption at low pH. Bioavailability and solubility of fomesafen in soil is affected by pH with a logarithmic acid dissociation constant
-1 -1 (pKa) equal to 2.7 with solubility of 50 mg L at pH 7 and less than 1 mg L at pH 1 (Shaner
2014, Weber 1993a, 1993b). Weber (1993b) suggested for weak acids like fomesafen, adsorption occurs by physical force near neutral pH and hydrophobic bonding or precipitation at low pH.
Guo et al. (2003) reported organic matter and pH were significantly correlated to fomesafen adsorption. Rauch et al. (2007) observed greater sweet corn (Zea mays L.) carry over injury from fomesafen treatments grown in areas with higher organic matter and lower pH. Weissler and
Poole (1982) leached fomesafen at 0.3 kg ai ha-1 with 0.66 L of water over nine weeks in four soils with 47% to 67% of applied fomesafen remaining at 0.0 to 0.1 m depth in a loam, loamy sand, and silty loam. However, mobility was greater in the coarse sand with 18% of fomesafen remaining at a 0.0 to 0.1 m depth. Weber (1993b) reported fomesafen exhibited higher mobility in the soil with greatest sand content when irrigated.
Small fruit and vegetable production in Florida is conducted on soils with typically high sand concentrations and low organic matter content that would indicate fomesafen has potential
61 to be mobile. However, Florida producers apply preemergence herbicides on top of a formed bed after fumigation and prior to laying plastic mulch. The use of plastic mulch may increase fomesafen persistence. Plastic mulch can influence pesticide persistence by limiting sunlight, reducing rainfall leaching, and affecting biological activity (Bond and Walker 1989; Jensen et al.
1989). Bond and Walker (1989) determined dissipation of linuron, pendimethalin, chlorobromuron, and flurochloridone was reduced when applied to soil under perforated polyethylene covers compared with bare soil. It took twice the amount of time for S-metolachlor to dissipate 50% under low-density polyethylene mulch (LDPE) (four days) than bare ground
(two days) (Grey et al. 2007). Plastic mulch may affect fomesafen dissipation especially as sunlight and rainfall exposure is reduced. Investigation into herbicide dissipation in plasticulture systems is needed to determine best management practices for future production. The objective of this research was to evaluate fomesafen persistence and movement in raised beds during
Florida strawberry (Fragaria × ananassa Duch.) production.
Material and Methods
Field experiments were conducted at the University of Florida Gulf Coast Research and
Education Center (GCREC), Balm, FL (27.76°N, 82.23°W), from September 2014 to February
2015 and August 2015 to March 2016, to investigate fomesafen persistence and movement in soil under Florida strawberry production system. Soil was a Myakka series fine sand (sandy, siliceous, hyperthermic Aeric Alaquods) with 1.5% organic matter, a pH of 6.5, and a sand, silt, clay content of 96%, 3%, and 1%, respectively. Raised beds were formed with bed pressing equipment with 1.2 m centers, a height of 0.3 m and bed top width of 0.7 m. Beds were fumigated with Telone C-35 (Dow AgroSciences, Indianapolis, IN), a combination of 63.4% 1,3- dichlopropene and 34.7% chloropicrin at 336 kg ha-1. Fumigants were injected with a three-
62 shank fumigation rig (Kennco Manufacturing, Ruskin, FL) at a 0.3 m depth in the bed. Herbicide was then applied and beds were covered with virtually impermeable film (VIF) (Berry Plastics
Corporation, Evansville, IN). Treatments included two rates of fomesafen (Reflex 2L Liquid
Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 and 0.84 kg ai ha-1, and a nontreated control. The fomesafen treatment at 0.42 kg ai ha-1 is a label use rate for Florida pepper and tomato production. Applications were made with CO2-pressured backpack sprayer
(Bellspray Inc., Opelousa, LA) calibrated to deliver 187 L ha-1 with a single DG 8002VS flat-fan nozzle (TeeJet, Spraying Systems Co., Wheaton, IL) on September 4, 2014 and August 27, 2015 to top of beds. Fertigation was applied through a single drip tape in the center of the bed with emitters every 0.3 m and a flow rate of 0.95 L min-1 per 30.0 m (Jain Irrigation Inc., Haines City,
FL). Rainfall and drip irrigation amount are listed in Table 4-1. Rainfall data acquired from
University of Florida Institute of Food and Agricultural Sciences Florida Automated Weather
Network from a weather station located at GCREC. Production and pest management practices were in accordance with industry standards and University of Florida Institute of Food and
Agricultural Sciences recommendations (Whitaker et al. 2015). Experimental design was a randomized complete block with four replications of 6.1 m plots with 1.5 m buffers between plots.
Bare root transplants of ‘Strawberry Festival’ were planted in two rows with 0.4 m spacing within rows on October 9, 2014 and October 8, 2015. Transplants received overhead watering during daylight hours for 14 consecutive days after transplanting to aid in establishment by maintaining high soil moisture levels until the root systems increase in size and plants start to actively grow and develop while avoiding desiccation of leaves. Strawberry damage ratings were taken 2, 4, and 8 weeks after transplant and were visually rated on a percent scale where 0
63 equaled no damage from the nontreated and 100 equaled complete desiccation. Weights of strawberry marketable yield were taken biweekly in 2014-2015 and 2015-2016 growing seasons with counts only taken in 2014-2015 growing season.
Soil Sampling and Analysis
Three 0.3 m core samples were collected in each plot treated with fomesafen at 0.42 kg ai ha-1: at day of application on September 4, 2014 and August 27, 2015; before strawberry transplant on October 3, 2014 and October 6, 2015; after transplant during overhead and drip irrigation on October 13, 2014 and October 20, 2015; after overhead irrigation was turned off on
November 20, 2014 and November 12, 2015; at beginning of harvest on January 13, 2015 and
January 7, 2016; and end of harvest on February 18 and March 8, 2016. Core samples were collected in the center of the bed next to the drip tape. The three core samples were divided into three 0.1 m depth increments of 0.0 to 0.1 m, 0.1 to 0.2 m, and 0.2 to 0.3 m. The soil corer had a
2.0 cm diameter resulting in each subsample having a volume of 31.4 cm3. For each plot the three subsamples at each depth were combined and mixed to form a single homogeneous sample for analysis. Samples were frozen at -20 °C until analysis. Sample extractions, high performance liquid chromatography (HPLC) and mass spectrometry analyses were conducted similar to
Syngenta protocols for determining residues of fomesafen in soil (Leung 1997; Lin 2009).
Extraction solution consisted of 10 mL HPLC water, 0.1 mL glacial acetic acid, and 10 mL methylene chloride for 10 g of air-dry soil sample. Preparation of samples for analysis included hand shaking solution, determining pH level ≤4.5, 60 minutes of machine shaking, 10 minutes of centrifugation at 5000 rpm to separate the phases, collection of methylene chloride layer with fomesafen residue, addition of 0.1 g of sodium sulfate to remove moisture, vacuum 2 mL of methylene chloride with fomesafen residue through 3 mL silica tubes (SampliQ Solid Phase
64 Extraction, Agilent Technologies, Santa Clara, CA) and rinsed out with 10 mL of ethyl acetate and collected, placed in 60 °C water bath with nitrogen gas to dry, addition of 1 mL of methanol placed on vortex for 1 minute alternating with 15 minutes of sonication for three repetitions before transfer to vials for analysis.
Analysis was performed using the Surveyor HPLC System (Thermo Fisher Scientific,
Waltham, MA). Each 25 µL sample was injected directly onto a Zorbax Eclipse plus-C18 (3.5
µm X2.1X100mm) analytical column (Agilent Technologies, Santa Clara, CA) at 25 °C. A gradient liquid chromatography method used mobile phases A (0.1% formic acid in water) and B
(0.1% formic acid in methanol) at a flow rate of 0.3 mL min-1. For mass spectrometry detection, the electrospray ionization source was operated in the negative ion mode and run with Xcalibur
2.0 software (Thermo Fisher Scientific, Waltham, MA). High purity nitrogen was used as the sheath (41 arb) and auxiliary (25 arb) gas and high-purity argon was used as the collision gas (1 mTorr). The parameters were as follows: spray voltage, 4.6 kV; capillary temperature, 280 °C; scan width for selected reaction monitoring (SRM), 0.1 m/z; scan time, 0.2 s. The peak width settings for both Q1 and Q3 were 0.7 m/z. The SRM ion pair transitions and collision energy
(CE) levels of each component were: parent, 437 m/z; quantifier product, 195 m/z, 40 CE; qualifier product 222 m/z, 33 CE. Recoveries from fortified nontreated soil samples indicated that recovery was 85±4%. The limit of detection for fomesafen was approximately 2.5 parts per billion (ppb).
Soil Moisture
Soil moisture samples were taken in the nontreated control plots on same day of persistence sampling with the same size soil corer. Three soil samples were taken at four placements of 0.0, 0.1, 0.2, and 0.3 m from the center of the bed and divided into three
65 subsamples at three depth increments of 0.0 to 0.1 m, 0.1 to 0.2 m, and 0.2 to 0.3 m. Each subsample was weighed then oven-dried at 60 °C for 96 hours and dry weight was taken to determine gravimetric water content. Soil moisture measurements (FieldScout TDR 100 Soil
Moisture Meter, Spectrum Technologies, Inc., Aurora, IL) were taken on day of treatment with three measurements taken in each nontreated plot randomly throughout the bed at a 0.2 m depth to determine volumetric water content. Soil bulk density in the bed was 1.51 g cm-3 and water content from day of treatment was converted to gravimetric. Gravimetric water content at 0.2 m depth on day of application averaged 0.07 for both 2014-2015 and 2015-2016 growing seasons.
Statistical Analysis
Strawberry tolerance data were analyzed in SAS (SAS® Institute v. 9.4, Cary, NC) using the mixed procedure with block as the random factor. Data were checked for normality and constant variance prior to analysis. Means were compared using the least squares means statement in SAS with the Tukey adjustment at P=0.05. Berry yields collected on multiple dates were analyzed using the repeated statement. Harvest dates by treatment interactions were not significant and total yields are presented.
Fomesafen concentration data for 0.0 to 0.1 m depth in soil was described with non-linear regression as performed with Sigmaplot 13.0 (Systat Software Inc. San Jose, CA) using a three- parameter logistic function
b f(x) = a/[1+(x/x0) ]
, where y is fomesafen concentration; x is days after treatment; a is the initial value of the response variable when x is zero; and b and x0 are parameters that determine dissipation curve.
Results and Discussion
Strawberry Tolerance
66 Fomesafen applications did not injure strawberry in either growing season (data not shown). Strawberry counts in 2014-2015 were similar across treatments (P=0.7257) averaging
589,401±21,511 berries ha-1. Growing season by treatment interaction was not detected for strawberry weights (P=0.8585) and seasons were combined. Total strawberry yield was similar across treatments (P=0.8155) and averaged 11,894±799 kg ha-1. Fomesafen safety on strawberry has been previously established. McGuire and Pitts (1991) demonstrated established matted-row strawberry plant tolerance to applications of fomesafen at 0.28 kg ai ha-1 following bed renovation. Fomesafen treatments caused foliar injury within 3 days after application with no injury symptoms evident 21 days after treatment due to new foliage development and no reduction in yield the following year. Boyd and Reed (2016) reported fomesafen at 0.42 and 0.84 kg ai ha-1 applied preemergence to the bed top did not cause injury or reduce yields of
‘Strawberry Festival’ and ‘WinterStar’ cultivars in the Florida production system. Fomesafen drip applied 1, 7, 15, and 30 days before transplanting at the same rates also did not reduce yields of ‘Strawberry Festival’.
Fomesafen Persistence and Movement
Fomesafen dissipation at 0.0 to 0.1 m depth had similar trends in both growing seasons
(Figure 4-1). Days required for 50% fomesafen dissipation were 37 and 47 for 2014-2015 and
2015-2016 growing seasons, respectively (Table 4-2). Fomesafen was detected in the 0.0 to 0.1 m soil depth at 167 and 194 days after treatment in 2014-2015 and 2015-2016 growing seasons, respectively. Fomesafen concentration decreased significantly at 0.0 to 0.1 m depth after transplant when overhead and drip irrigation was initiated. Fomesafen concentration was less than 25 ppb on any sampling date for 0.1 to 0.2 m and 0.2 to 0.3 m depths. It is reasonable to speculate that the majority of fomesafen may have leached out of the sampling zone during this
67 irrigation period even though greater herbicide concentrations were not determined at greater depths on sampling dates after transplant with days of overhead and drip irrigation having occurred. Fomesafen potential for leaching in sandy soils has been established (Weber 1993b;
Weissler and Poole 1982). Gravimetric water content throughout the bed was at least twice as great at sampling dates with irrigation compared with moisture levels prior to irrigation (Figure
4-2). Water content was greatest at the center of the bed where fomesafen concentration samples were taken. Soil moisture content can influence herbicide dissipation in the soil. Typically, rates of herbicide loss increase with greater moisture (Bond and Walker 1989). Although, at the depth sampled, fomesafen concentration observed over time is greater than previous research conducted on sandy soils in open field production (Li 2014). Fomesafen dissipation instead was similar to silt or clay based soils in open field production even with rapid concentration decline after strawberry transplant (Cobucci et al. 1998; Mueller et al. 2014; Rauch et al. 2007).
The majority of fomesafen dissipated from the top 0.1 m of soil in the Florida strawberry production system with concentration decreasing significantly after transplant. Fomesafen residual persisted throughout the growing season, but limited herbicide concentrations after transplant may affect weed control efficacy that is needed throughout production. Strawberry was unaffected by fomesafen treatments, however exposure to herbicide may have been limited after transplant. Additional research is warranted to further determine fomesafen dissipation throughout the entire bed and evaluate environmental concern of potential fomesafen leaching.
68 Table 4-1. Rainfall, drip irrigation, and overhead irrigation between soil sampling dates during field experiments, 2014-2015 and 2015-2016, Balm, FL. Growing season Time perioda Rainfall Drip irrigation Overhead irrigation DATb ------L m-2 ------L m-2 ------L m-2 ------2014-2015 0-28 305 0 0 29-38 11 26 284 39-76 103 250 462 77-130 147 355 0 131-167 126 314 59c 2015-2016 0-39 116 0 0 40-53 8 79 675 54-76 30 151 71 77-132 86 369 0 133-194 209 520 0 aFive time periods for each growing season follow soil persistence samplings and are application to before transplant; before transplant to after transplant during overhead and drip irrigation; after transplant to after overhead irrigation; after overhead irrigation to harvest; and harvest period. bDAT = days after treatment. cOverhead irrigation used for strawberry freeze protection.
69 Figure 4-1. Fomesafen concentration in soil at three depth from field experiments, 2014-2015 and 2015-2016, Balm, FL. A) 2014- 2015 growing season. B) 2015-2016 growing season. Error bars represent standard error of the mean. Data described by three-parameter logistic model and parameter estimates for fomesafen concentrations in soil at 0.0 to 0.1 m depth are listed in Table 2.
70 Table 4-2. Parameter estimates of fomesafen concentration in soil at 0.0 to 0.1 m depth from field experiments, 2014-2015 and 2015- 2016, Balm, FL. a 2 b Growing season a±SE b±SE x0±SE r DT50 P value 2014-2015 164.1±11.8 16.0±9.4 36.9±2.4 0.99 37 0.0018 2015-2016 167.2±16.7 12.6±4.7 46.8±2.8 0.97 47 0.0054 b Three-parameter logistic f(x) = a/[1+(x/x0) ] was used for regression, where y is fomesafen concentration; x is days after treatment; a is the initial value of the response variable when x is zero; and b and x0 are parameters that determine dissipation curve. aSE = standard error of the mean. b DT50 = days required for 50% fomesafen dissipation.
71 Figure 4-2. Gravimetric water content in four placements from the center of the bed for three depths at five sampling dates from nontreated control plots, 2014-2015 and 2015- 2016, Balm, FL. A) 2014-2015 0.0 m. B) 2014-2015 0.1 m. C) 2014-2015 0.2 m. D) 2014-2015 0.3 m. E) 2015-2016 0.0 m. F) 2015-2016 0.1 m. G) 2015-2016 0.2 m. H) 2015-2016 0.3 m. Error bars represent 95% confidence interval for the mean.
72 CHAPTER 5 EFFECT OF FUMIGATION ON FOMESAFEN DISSIPATION
Introduction
Fomesafen is a diphenylether that inhibits the protoporphyrinogen oxidase (Protox) enzyme and is primarily used for broadleaf weed control. Protox catalyzes the conversion of protoporphyrinogen IX to protoporphyrin IX as part of the biosynthesis of tetrapyrroles such as chlorophyll (Duke et al. 1991; Scalla and Matringe 1994). The herbicidal effects of Protox inhibitors are relatively quick due to fast build up of substrates rather than from the depletion of chlorophyll (Becerril and Duke 1989).
Fomesafen has the potential to be used as an alternative mechanism of action for preemergence nutsedge (Cyperus spp.) control in Florida plasticulture production of small fruit and vegetables. Drip applied fomesafen at 0.28 kg ai ha-1 reduced yellow nutsedge (Cyperus esculentus L.) punctures of mulch 89% at 56 days after treatment (Monday et al. 2015). In
Florida, Miller and Dittmar (2014) stated that preemergence applications of fomesafen at 0.42 kg ai ha-1 controlled 52% of a mix of purple (Cyperus rotundus L.) and yellow nutsedge 11 weeks after treatment, however Boyd (2015) reported fomesafen application alone did not reduce purple nutsedge populations in tomato production.
Fomesafen is a weak acid with increased sorption at low pH. Bioavailability and solubility of fomesafen in soil is affected by pH with a logarithmic acid dissociation constant
-1 -1 (pKa) equal to 2.7 with solubility of 50 mg L at pH 7 and less than 1 mg L at pH 1 (Shaner,
2014, Weber 1993a, 1993b). Previous research indicates fomesafen dissipation varies under different soil and environmental conditions. Fomesafen photodecomposes readily under relatively low sunlight conditions and degrades rapidly under anaerobic conditions with a half- life less than three weeks (Shaner 2014, Wauchope et al. 1992). Fomesafen half-life was reported
73 from 28 to 66 days, after 0.18 kg ai ha-1 alone or 0.09 followed by 0.18 kg ai ha-1 applications in a Madalin silty clay loam (Rauch et al. 2007). Mueller et al. (2014) reported fomesafen half-life over three experimental years on a loam soil averaged 46 days. Li (2014) reported the half-life of fomesafen applied at 0.28 and 0.56 kg ai ha-1 was 6 and 4 days, respectively, for Cecil Tifton loamy sand, and was not detectable past 28 days.
Florida producers apply preemergence herbicides on top of a formed bed after fumigation and prior to laying plastic mulch. Bond and Walker (1989) showed that dissipation of linuron, pendimethalin, chlorobromuron, and flurochloridone was reduced when applied to soil under perforated polyethylene covers compared with bare soil. It took twice the amount of time for S- metolachlor to dissipate 50% under low-density polyethylene mulch compared with bare ground
(Grey et al. 2007). Persistence under plastic may be an issue for vegetable growers especially those that double crop.
Fumigation in combination with the use of plastic mulch may also increase herbicide persistence as microbial populations and enzymatic activity in the soil can be altered with fumigant use (Klose et al. 2006; Ladd et al. 1976; Yamamoto et al. 2008). EPTC half-life was 9 days, but when applied in conjunction with metam sodium the half-life increased to 22 days
(Stiles et al. 2000). Feng et al. (2012) demonstrated fomesafen degradation by microbial activity.
This may affect fomesafen dissipation particularly as sunlight exposure is reduced with plastic mulch. Investigation into herbicide dissipation in plasticulture systems is needed to determine best management practices for future production. The objective of this research was to evaluate the effect of fumigation on fomesafen dissipation, eggplant (Solanum melngena L.) tolerance to fomesafen, and fomesafen control of purple nutsedge.
Material and Methods
74 Field experiments were conducted at the University of Florida Gulf Coast Research and
Education Center (GCREC), Balm, FL (27.76°N, 82.23°W), in 2015 and 2016. Soil was a
Myakka series fine sand (sandy, siliceous, hyperthermic Aeric Alaquods) with 1.0% organic matter, a pH of 6.8, and a sand, silt, clay content of 95%, 4%, and 1%, respectively at the 2015 experiment site and 1.5% organic matter, a pH of 6.0, and a sand, silt, clay content of 98%, 1%, and 1%, respectively at the 2016 site. Treatments were fomesafen (Reflex 2L Liquid Herbicide,
Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 kg ai ha-1, an industry standard for nutsedge control S-metolachlor (Dual Magnum, Syngenta Crop Protection LLC, Greensboro,
NC) at 1.06 kg ai ha-1 and a nontreated control in either a fumigated bed or not. Treatments that included fumigation had Pic-Clor 60 (Soil Chemicals Corporation, Hollister, CA), a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha-1 injected into the bed.
Fumigants were injected with a three-shank fumigation rig (Kennco Manufacturing, Ruskin, FL) at a 0.2 m depth in the bed. The rate for fomesafen is currently labeled for use in Florida tomato and pepper production. Herbicide applications were made with CO2-pressured backpack sprayer
(Bellspray Inc., Opelousa, LA) calibrated to deliver 187 L ha-1 with a single 8002VS flat-fan nozzle (TeeJet, Spraying Systems Co., Wheaton, IL) to top of preformed beds with 1.2 m centers, a height of 0.3 m and bed top width of 0.7 m. Treatments were made August 11, 2015 and January 25, 2016. Immediately after bed fumigation and herbicide application each bed was covered with 0.03 mm thick virtually impermeable film (VIF) (Blockade, Berry Plastics
Corporation, Evansville, IN). Fertigation was applied through two rows of drip tape separated by
0.2 m buried just beneath the surface of the bed with emitters every 0.3 m and a flow rate of 0.95
L min-1 per 30.0 m (Jain Irrigation Inc., Haines City, FL). Growing season rainfall and drip irrigation amount are listed in Table 5-1. Rainfall data acquired from University of Florida
75 Institute of Food and Agricultural Sciences Florida Automated Weather Network from a weather station located at GCREC.
The experiment was a split-plot design organized as a randomized complete block with four replications. Each main plot was 21.3 m of a single bed with 1.5 m buffers between plots.
The main plot factors were the presence or absence of fumigation. Each main plot consisted of three 6.1 m subplots with 1.5 m buffers. Three 0.1 m core samples were collected in each fomesafen applied subplot on the day of treatment (August 11, 2015 and January 25, 2016), transplant (September 2, 2015 and March 9, 2016), and at the end of the trial (December 8, 2015 and May 31, 2016). The soil corer diameter was 2.0 cm with each sample having a volume of
31.4 cm3. For each fomesafen subplot the three samples were combined and homogenized for analysis. Samples were kept frozen at -20 °C until analysis. Sample extractions, high performance liquid chromatography (HPLC) and mass spectrometry analyses were conducted similar to Syngenta protocols for determining residues of fomesafen in soil (Leung 1997; Lin
2009). Extraction solution consisted of 10 mL HPLC water, 0.1 mL glacial acetic acid, and 10 mL methylene chloride for 10 g of air-dry soil sample. Preparation of samples for analysis included hand shaking solution, determining pH level ≤4.5, 60 minutes of machine shaking, 10 minutes of centrifugation at 5000 rpm to separate the phases, collection of methylene chloride layer with fomesafen residue, addition of 0.1 g of sodium sulfate to remove moisture, vacuum 2 mL of methylene chloride with fomesafen residue through 3 mL silica tubes (SampliQ Solid
Phase Extraction, Agilent Technologies, Santa Clara, CA) and rinsed out with 10 mL of ethyl acetate and collected, placed in 60 °C water bath with nitrogen gas to dry, addition of 1 mL of methanol placed on vortex for 1 minute alternating with 15 minutes of sonication for three repetitions before transfer to vials for analysis.
76 Analysis was performed using the Surveyor HPLC System (Thermo Fisher Scientific,
Waltham, MA). Each 25 µL sample was injected directly onto a Zorbax Eclipse plus-C18 (3.5
µm X2.1X100mm) analytical column (Agilent Technologies, Santa Clara, CA) at 25 °C. A gradient liquid chromatography method used mobile phases A (0.1% formic acid in water) and B
(0.1% formic acid in methanol) at a flow rate of 0.3 mL min-1. For Mass spectrometry detection, the electrospray ionization source was operated in the negative ion mode and run with Xcalibur
2.0 software (Thermo Fisher Scientific, Waltham, MA). High purity nitrogen was used as the sheath (41 arb) and auxiliary (25 arb) gas and high-purity argon was used as the collision gas (1 mTorr). The parameters were as follows: spray voltage, 4.6 kV; capillary temperature, 280 °C; scan width for selected reaction monitoring (SRM), 0.1 m/z; scan time, 0.2 s. The peak width settings for both Q1 and Q3 were 0.7 m/z. The SRM ion pair transitions and collision energy
(CE) levels of each component were: parent 437 m/z; quantifier product, 195 m/z, 40 CE; qualifier product 222 m/z, 33 CE. Recoveries from fortified nontreated soil samples indicated that recovery was 92±3%. The limit of detection for fomesafen was approximately 2.5 parts per billion (ppb).
Hybrid ‘Night Shadow’ eggplant (Siegers Seed Co., Holland, MI) was transplanted
September 2, 2015 and in March 9, 2016 in the bed in a single row with 0.6 m spacing with 10 plants per subplot. Production and pest management practices were in accordance with industry standards and University of Florida Institute of Food and Agricultural Sciences recommendations (McAvoy et al. 2015). Crop visual injury ratings on a percent scale where 0 equaled no visible chlorosis or stunting and 100 equaled complete desiccation were taken at 2, 4, and 6 weeks after transplant (WATr). Eggplant heights were taken at 6 WATr on five plants per subplot. Counts and weights per subplot of eggplant marketable yield were taken weekly on six
77 and five occasions in 2015 and 2016, respectively. Purple nutsedge counts per subplot were taken 1 and 2 months after treatment.
Fomesafen dissipation data were subjected to ANOVA at the 0.05 probability level in
SAS (SAS® Institute v. 9.4, Cary, NC) using the mixed procedure with block as random factor.
Eggplant tolerance and nutsedge density data were subjected to ANOVA at the 0.05 probability level in SAS using the mixed procedure with block and block x main plot as the random factors.
Data were checked for normality and constant variance prior to analysis. Means were compared using the least squares means statement with the Tukey adjustment at p=0.05. Fomesafen concentration, eggplant injury, counts, weights, and purple nutsedge counts after transplant were collected on multiple dates and were analyzed using the repeated statement. Fomesafen dissipation data is presented by growing season. Growing season by fumigant and herbicide interactions were not detected and seasons were combined. Harvest date and nutsedge counts by fumigant and herbicide interactions were not significant and total yields and average nutsedge density is presented.
Results and Discussion
Fomesafen Dissipation
Fomesafen dissipated throughout the growing season for each treatment. Fomesafen concentrations across treatments at transplant were similar to concentrations at application
(Table 5-2). Fomesafen concentration in soil decreased 83% and 96% from application to harvest in 2015 and 2016, respectively. Fumigation did not affect fomesafen dissipation on any sampling date. This is similar to laboratory experiments that found soil microorganisms had minimal effect on fomesafen degradation (Li 2014). At the depth sampled, fomesafen concentration observed over time is greater than previous research conducted on sandy soils. In open field production, Li
78 (2014) reported the half-life of fomesafen applied at 0.28 and 0.56 kg ai ha-1 was 6 and 4 days, respectively, for a Cecil Tifton loamy sand, and was not detectable past 28 days. Weissler and
Poole (1982) leached fomesafen at 0.30 kg ai ha-1 with 0.66 L of water over nine weeks in four soils with 47% to 67% of applied fomesafen remaining at 0.0 to 0.1 m depth in a loam, loamy sand, and silty loam. However, mobility was greater in the coarse sand with 18% of fomesafen remaining at a 0.0 to 0.1 m depth. Small fruit and vegetable production in Florida is conducted on soils with typically high sand concentrations that would indicate fomesafen has potential to leach. However, fomesafen dissipation was similar to silt or clay based soils in open field production that were exposed to rainfall (Cobucci et al. 1998; Mueller et al. 2014; Rauch et al.
2007). In plasticulture systems, mobility may be reduced as solute movement is primarily influenced by localized, drip irrigation that is optimized to prevent leaching below crop root zone. This could decrease fomesafen dissipation more than what would be expected on a sandy soil from leaching.
Eggplant Tolerance
Similar injury was observed with herbicides regardless of fumigant application (Table 5-
3). Fomesafen injured eggplant 11% to 14% at 2 and 4 WATr, but damage decreased over time.
S-metolachlor caused less than 5% injury on all evaluation dates. Eggplant recovered from initial injury and heights were similar across treatments (P=0.8683) averaging 53±1 cm at 6 WATr.
Eggplant counts (P=0.7543) and total yield (P=0.6854) were similar across treatments averaging
121,095±5,382 fruit ha-1 and 53,290±2722 kg ha-1, respectively. Chaudhari et al. (2016) reported eggplant tolerance to fomesafen with or without tomato rootstocks. Fomesafen applied at 0.42 kg ai ha-1 to the bed top one day prior to transplant caused no eggplant stand loss or reduction in yield, height, or biomass. Injury was observed in one growing season with 12% and 3% injury at
79 one and four weeks after treatment, respectively. Fomesafen applications appear to be safe for use in eggplant even if early season damage is observed.
Nutsedge Control
Fumigation did not affect purple nutsedge density (Table 5-4). S-metolachlor applications reduced nutsedge density 48% compared to treatments with no herbicide. Fomesafen applications had similar nutsedge density as S-metolachlor and no herbicide treatments. Boyd
(2015) and Boyd and Reed (2016) noted that fomesafen did not consistently control purple nutsedge in tomato and strawberry production.
The majority of fomesafen dissipated throughout the growing season from the top 0.1 m regardless of fumigation in the plasticulture system. Preemergence applications do not adequately control purple nutsedge, but further evaluation for broadleaf control is warranted.
Eggplant is tolerant of fomesafen providing comparable yields to industry standards, and may be of use as a management tool for broadleaf weeds. However, early season injury is a concern.
Further research is necessary to determine the half-life of fomesafen in Florida vegetable plasticulture production and to identify the means of dissipation.
80 Table 5-1. Rainfall and drip irrigation between soil sampling dates during field experiments, 2015 and 2016, Balm, FL. Rainfall Drip irrigation Sampling perioda 2015 2016 2015 2016 ------L m-2 ------L m-2 ------Application to transplant 135 98 18 35 Transplant to harvest 205 360 1720 1474 aApplication, transplant, and harvest were 0, 22, and 119 days after treatment, respectively (2015) and 0, 44, and 128 days after treatment, respectively (2016).
81 Table 5-2. Fomesafen concentrations in soil averaged across nontreated and fumigated fomesafen treatments in field experiments, 2015 and 2016, Balm, FL. Fomesafen concentration Sampling datea 2015 2016 ------ppbb ------6 Application 282±26c ad 268±44 a - Transplant 162±42 ab 159±54 a Harvest 48±35 b 12±7 b Sampling date 0.0009 0.0053 Fumigation 0.8827 0.9427 Sampling date*fumigation 0.6247 0.9598 aSoil cores were taken at application, transplant, and harvest at 0, 22, and 119 days after treatment, respectively (2015) and 0, 44, and 128 days after treatment, respectively (2016). bppb = parts per billion. cStandard error of the mean. dMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons. Treatments included fomesafen (Reflex 2L Liquid Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 kg ai ha-1 and treatments with fumigation had Pic-Clor 60 (Soil Chemicals Corporation, Hollister, CA), a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha-1.
82 Table 5-3. Eggplant injury after transplant from applications of fumigation and herbicide combinations in combined field experiments, 2015 and 2016, Balm, FL. Eggplant injury (WATra) Fumigationb 2 4 6 ------% ------Nontreated 10 9 5 1,3-D+chloropicrin 7 4 2 Herbicidec Fomesafen 14 ad 11 a 4 S-metolachlor 3 b 3 b 2 Fumigation 0.5129 0.2188 0.2132 Herbicide 0.0047 0.0106 0.2207 Fumigation*herbicide 0.7149 0.4769 0.3548 aWATr = weeks after transplant, no injury observed at 8 WATr in either year. bTreatments with fumigation had Pic-Clor 60 (Soil Chemicals Corporation, Hollister, CA), a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha-1. cHerbicide treatments were fomesafen (Reflex 2L Liquid Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 kg ai ha-1 and S-metolachlor (Dual Magnum, Syngenta Crop Protection LLC, Greensboro, NC) at 1.06 kg ai ha-1. dMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
83 Table 5-4. Purple nutsedge density averaged across evaluation dates that were one and two months after treatment with fumigant and herbicide combinations in field experiments, 2015 and 2016, Balm, FL. Fumigationa Nutsedge density # m-2 Nontreated 30 1,3-D+chloropicrin 17 Herbicideb Nontreated 33 ac Fomesafen 21 ab S-metolachlor 17 b Fumigation 0.0770 Herbicide 0.0307 Fumigation*herbicide 0.5770 aTreatments with fumigation had Pic-Clor 60 (Soil Chemicals Corporation, Hollister, CA), a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha-1. bHerbicide treatments were fomesafen (Reflex 2L Liquid Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 kg ai ha-1 and S-metolachlor (Dual Magnum, Syngenta Crop Protection LLC, Greensboro, NC) at 1.06 kg ai ha-1. cMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
84 CHAPTER 6 EVALUATION OF PLASTIC MULCH ON FOMESAFEN DISSIPATION
Introduction
Fomesafen is a protoporphyrinogen oxidase (Protox) inhibitor and has the potential to be used as an alternative mechanism of action for preemergence nutsedge (Cyperus spp.) control in
Florida small fruit and vegetable production. Fomesafen inhibits the protoporphyrinogen oxidase
(Protox) enzyme that catalyzes the conversion of protoporphyrinogen IX (Proto IX) to protoporphyrin IX as part of the biosynthesis of tetrapyrroles (Duke et al. 1991; Scalla and
Matringe 1994). The accumulation of Proto IX in the presence of light leads to lipid peroxidation and cell death (Becerril and Duke 1989; Scalla and Matringe 1994). Fomesafen preemergence treatments have shown the ability to suppress or control yellow nutsedge growth (Dowler 1987;
Monday et al. 2015; Wilcut et al. 1997). However, limited fomesafen efficacy on purple nutsedge has been demonstrated in Florida plasticulture production. Miller and Dittmar (2014) reported preemergence applications of fomesafen 0.42 kg ai ha-1 controlled a mix of purple and yellow nutsedge 50% at 28 days after treatment. Fomesafen application alone did not reduce purple nutsedge populations in strawberry production (Boyd 2015; Boyd and Reed 2016).
Fomesafen photodecomposes readily under relatively low sunlight conditions and degrades rapidly under anaerobic conditions with a half-life less than three weeks (Shaner 2014).
Li (2014) reported lab incubated fomesafen had minimal degradation by soil microorganisms and biological degradation is unlikely to be a major pathway for fomesafen dissipation under aerobic conditions in the field. Fomesafen is a weak acid with increased sorption at low pH.
Bioavailability and solubility of fomesafen in soil is affected by pH with a logarithmic acid
-1 dissociation constant (pKa) equal to 2.7 with solubility of 50 mg L at pH 7 and less than 1 mg
L-1 at pH 1 (Shaner 2014, Weber 1993a, 1993b). Organic matter and pH are significantly
85 correlated to fomesafen adsorption and fomesafen has exhibited greater mobility in sandier soils
(Guo et al. 2003; Weber 1993b). Fomesafen open field half-life was reported from 28 to 66 days, after 0.18 kg ai ha-1 alone or 0.09 followed by 0.18 kg ai ha-1 applications with residue still detectable 350 days after treatment in a Madalin silty clay loam (Rauch et al. 2007). Mueller et al. (2014) reported fomesafen half-life over three experimental years on a loam soil averaged 46 days. On a Tifton loamy sand six and four days were required for 50% fomesafen dissipation for rates of 0.28 and 0.56 kg ai ha-1, respectively (Li 2014). Fomesafen persistence may increase in plasticulture production.
Plastic mulches are used in Florida small fruit and vegetable production to protect raised beds from erosion, decrease soil moisture evaporation, improve fumigant efficacy, extend weed control, and alter soil temperature in the root zone. Pesticide dissipation is affected by plastic mulch, which can influence pesticide persistence by limiting sunlight, leaching by rainfall, and affecting biological activity (Bond and Walker 1989; Jensen et al. 1989). Bond and Walker
(1989) determined dissipation of linuron, pendimethalin, chlorobromuron, and flurochloridone was reduced when applied to soil under perforated polyethylene covers compared with bare soil.
It took twice the amount of time for S-metolachlor to dissipate 50% under low-density polyethylene mulch (LDPE) (four days) than bare ground (two days) (Grey et al. 2007). Delayed dissipation of pesticides applied to soil under black polyethylene covers has been previously established, however there is a lack of research on fomesafen dissipation in plasticulture production and dissipation of herbicides under virtually impermeable film (VIF) and totally impermeable film (TIF). In Florida production systems, VIF and TIF mulches are most widely used and are multi-layer films which contain barrier polymers such as polyamide (nylon) or ethylene vinyl alcohol (EVOH) compressed between other layers of polymer that bind the
86 polyethylene outer layer to the barrier layer. Films containing an EVOH barrier layer are currently referred to as TIF (Qin et al. 2011). Films containing barrier polymers are significantly less permeable to fumigants than LDPE and high density polyethylene mulches (HDPE)
(Chellemi et al. 2011; Gamliel et al. 1998; Ou et al. 2007; Qin et al. 2011; Santos et al. 2007;
Wang et al. 1998). Gamliel et al. (1998) reported a 100 μm thick LDPE film was over 150 fold more permeable to methyl bromide, than a 30 μm mulch containing an EVOH barrier layer.
Many growers in Florida double crop, and fomesafen’s potential to persist at a high concentration under plastic may dissuade producers from using the herbicide to avoid limitations on which fruit or vegetable crops can be planted back into beds without fear of injury.
Investigation into herbicide dissipation in plasticulture systems is needed to determine best management practices for future production. The objective of this research was to evaluate fomesafen efficacy, squash (Cucurbita pepo L.) tolerance, and the effect of different plastic mulches on fomesafen dissipation.
Material and Methods
Field experiments were conducted at the University of Florida Gulf Coast Research and
Education Center (GCREC), Balm, FL (27.76°N, 82.23°W), in 2015 and 2016. Soil was a
Myakka series fine sand (sandy, siliceous, hyperthermic Aeric Alaquods) with 1.0% organic matter, a pH of 6.8, and a sand, silt, clay content of 95%, 4%, and 1%, respectively at the 2015 experiment site and 1.5% organic matter, a pH of 6.0, and a sand, silt, clay content of 98%, 1%, and 1%, respectively at the 2016 site. Treatments included fomesafen (Reflex 2L Liquid
Herbicide, Syngenta Crop Protection, LLC, Greensboro, NC) at 0.42 kg ai ha-1 under no plastic mulch, clear mulch (0.02 mm, Poly Expert Inc., Laval, QC Canada), low density polyethylene mulch (LDPE) (0.02 mm, FilmTech Corp., Allentown, PA), virtually impermeable film (VIF)
87 (0.03 mm, ‘Blockade’, Berry Plastics Corporation, Evansville, IN), and totally impermeable film
(TIF) (0.03 mm, Guardian Ag Plastics, Tampa, FL). The rate for fomesafen is currently labeled for use in Florida tomato and pepper production. Raised beds were formed with bed pressing equipment with 1.2 m centers, a height of 0.3 m and bed top width of 0.7 m. Beds were fumigated with Pic-Clor 60 (Soil Chemicals Corporation, Hollister, CA), a combination of 39%
1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha-1 prior to fomesafen application.
Fumigant was injected with a three-shank fumigation rig (Kennco Manufacturing, Ruskin, FL) at a 0.2 m depth. Fomesafen applications were made with CO2-pressured backpack sprayer
(Bellspray Inc., Opelousa, LA) calibrated to deliver 187 L ha-1 with a single 8002VS nozzle
(TeeJet, Spraying Systems Co., Wheaton, IL) to the top of preformed beds. Each bed was covered with plastic mulch of according treatment immediately after herbicide application.
LDPE, VIF, and TIF were black/white mulches with white side up in 2015 and black in 2016.
Fumigation and herbicide applications were made August 21, 2015 and February 16, 2016.
Fertigation was applied through two rows of drip tape separated by 0.2 m buried just beneath the surface of the bed with emitters every 0.3 m and a flow rate of 0.95 L min-1 per 30.0 m (Jain
Irrigation Inc., Haines City, FL). Rainfall and drip irrigation amounts are listed in Table 6-1.
Rainfall data was acquired from University of Florida Institute of Food and Agricultural
Sciences Florida Automated Weather Network from a weather station located at GCREC. Soil volumetric moisture (Soil Moisture Smart Sensor S-SMC-M005, Onset Computer Corporation,
Bourne, MA) and soil temperature (12-Bit Temperature Smart Sensor, Onset Computer
Corporation, Bourne, MA) measurements at a 0.1 m depth were data logged hourly (HOBO®
Micro Station, Onset Computer Corporation, Bourne, MA) throughout the trial in each plot.
88 Experiment was a randomized complete block with four replications of 7.6 m plots.
Three 0.1 m core samples were collected in each plot at day of application (August 21, 2015 and
February 16, 2016), transplant (September 21, 2015 and March 9, 2016), and at the end of the trial (December 2, 2015 and May 9, 2016). The soil corer diameter was 2.0 cm with each sample having a volume of 31.4 cm3. In each plot, the three samples were combined and mixed to form a single homogeneous sample. Samples were frozen at -20 °C until analysis. Sample extractions, high performance liquid chromatography (HPLC) and mass spectrometry analyses were conducted similar to Syngenta protocols for determining residues of fomesafen in soil (Leung
1997; Lin 2009). Extraction solution consisted of 10 mL HPLC water, 0.1 mL glacial acetic acid, and 10 mL methylene chloride for 10 g of air-dry soil sample. Preparation of samples for analysis included hand shaking solution, determining pH level ≤4.5, 60 minutes of machine shaking, 10 minutes of centrifugation at 5000 rpm to separate the phases, collection of methylene chloride layer with fomesafen residue, addition of 0.1 g of sodium sulfate to remove moisture, vacuum 2 mL of methylene chloride with fomesafen residue through 3 mL silica tubes (SampliQ
Solid Phase Extraction, Agilent Technologies, Santa Clara, CA) and rinsed out with 10 mL of ethyl acetate and collected, placed in 60 °C water bath with nitrogen gas to dry, addition of 1 mL of methanol placed on vortex for 1 minute alternating with 15 minutes of sonication for three repetitions before transfer to vials for analysis.
Analysis was performed using the Surveyor HPLC System (Thermo Fisher Scientific,
Waltham, MA). Each 25 µL sample was injected directly onto a Zorbax Eclipse plus-C18 (3.5
µm X2.1X100mm) analytical column (Agilent Technologies, Santa Clara, CA) at 25 °C. A gradient liquid chromatography method used mobile phases A (0.1% formic acid in water) and B
(0.1% formic acid in methanol) at a flow rate of 0.3 mL min-1. For mass spectrometry detection,
89 the electrospray ionization source was operated in the negative ion mode and run with Xcalibur
2.0 software (Thermo Fisher Scientific, Waltham, MA). High purity nitrogen was used as the sheath (41 arb) and auxiliary (25 arb) gas and high-purity argon was used as the collision gas (1 mTorr). The parameters were as follows: spray voltage, 4.6 kV; capillary temperature, 280 °C; scan width for selected reaction monitoring (SRM), 0.1 m/z; scan time, 0.2 s. The peak width settings for both Q1 and Q3 were 0.7 m/z. The SRM ion pair transitions and collision energy
(CE) levels of each component were: parent, 437 m/z; quantifier product, 195 m/z, 40 CE; qualifier product 222 m/z, 33 CE. Recoveries from fortified nontreated soil samples indicated that recovery was 94±2%. The limit of detection for fomesafen was approximately 2.5 parts per billion (ppb).
Hybrid ‘Sunburst’ yellow scallop squash (Siegers Seed Co., Holland, MI) was transplanted in the bed in a single row with 0.6 m spacing with 10 plants per plot. Production and pest management practices were in accordance with industry standards and University of Florida
Institute of Food and Agricultural Sciences recommendations (Freeman et al. 2015). Squash visual injury ratings on a percent scale where 0 equaled no visible chlorosis and 100 equaled complete desiccation were taken at 2, 4, and 8 weeks after transplanting (WATr). Squash heights were taken 2 and 4 WATr and were an average of three plants per plot. Counts and weights per plot of squash yield were taken at a single harvest. Purple nutsedge density was taken at transplant and harvest. Purple nutsedge was counted by number pierced through plastic in mulch treatments and were taken as an average of three densities per plot using a 0.6 m2 grid.
Data were subjected to ANOVA at the 0.05 probability level in SAS (SAS® Institute v.
9.4, Cary, NC) using the mixed procedure with block as random factor. Data were checked for normality and constant variance prior to analysis. Means were compared using the least squares
90 means statement with the Tukey adjustment at p=0.05. Squash heights, purple nutsedge counts, fomesafen concentration for each treatment were collected on multiple dates and were analyzed using the repeated statement. Fomesafen dissipation data was described by growing season.
Growing season by treatment interaction was not detected for squash injury (P=0.4410), squash height (P=0.3378), and nutsedge density (P=0.3259) and, thus, seasons were combined. Growing season by treatment interaction was detected for squash fruit number ha-1 (P=0.0478) and squash kg ha-1 yield (P=0.0343) seasons were analyzed separately.
Results and Discussion
Fomesafen Dissipation
Fomesafen concentration for all treatments was similar at application ranging from 139 to
184 ppb and 138 to 176 ppb in 2015 and 2016, respectively (Table 6-2). Fomesafen concentrations under LDPE, VIF, and TIF mulches were similar on all sampling dates as were clear and no mulch treatments. At transplant in both growing seasons treatments with LDPE,
VIF, and TIF black/white mulch had greater than twofold the fomesafen concentrations than treatments with clear or no mulch. At harvest in 2015, LDPE, VIF, and TIF treatments had greater fomesafen concentrations than clear and no mulch treatments, however in 2016 concentrations were similar for all treatments. Clear and no mulch treatments had lower fomesafen concentrations at transplant than application. Black/white mulch had similar fomesafen concentrations across all sampling dates in both growing seasons except for TIF at harvest in 2016. Fomesafen can persist at high concentrations throughout the growing season in
Florida plasticulture production and may limit growers on what upcoming crops can be planted in the treated area.
Fomesafen persisting at greater concentrations under black/white plastic mulch is similar
91 to previous research (Bond and Walker 1989; Grey et al. 2007). Black/white mulch treatments may have reduced fomesafen dissipation by limiting sunlight penetration compared with clear mulch and bare ground treatments. Fomesafen readily photodecomposes and bed top applications leave the herbicide exposed to sunlight (Shaner 2014). Greater fomesafen dissipation for bare ground treatment may further been influenced by rainfall leaching (Figure 6-1). Fomesafen potential for leaching in sandy soils has been established (Weber 1993b; Weissler and Poole
1982). In 2016, rainfall may have influenced fomesafen concentrations at harvest across mulch treatments. Before the harvest sampling date a period of 26 days with less than 1.00 cm of rainfall followed by 7.98 cm of rainfall in one day that caused flooding. Throughout both growing seasons volumetric water content in the top center of the bed was affected by rainfall.
Degradation of herbicides in soil can be influenced by temperature and soil moisture content. Typically, rates of herbicide loss increase with greater temperature and moisture (Bond and Walker 1989). The no mulch and clear mulch treatments had the most extreme cool and warm temperatures, respectively (Figure 6-2). In 2015, the clear mulch had daily maximum temperatures reaching 40 °C on 40% of experimental days. In 2016, the treatment without mulch had 90% of average daily temperatures below 25 °C. The type of black/white mulch did not influence fomesafen concentrations on sampling dates and appeared to have had similar soil moisture and temperature.
Squash Tolerance
Fomesafen applications caused similar injury to squash (P=0.7349) across all treatments averaging 3±1% at 2 WATr and no injury was observed at later evaluation dates. Squash height measurement date by treatment interaction was not significant (P=0.4498) and was averaged over evaluations. Squash height was similar across treatments (P=0.1309) averaging 27±1 cm.
92 Squash yield in yield in kg ha-1 and fruit number ha-1 was greater in LDPE, VIF, and TIF mulch treatments than no mulch treatment in 2015 and 2016 growing seasons. Squash fruit number ha-1 was similar across treatments with plastic mulch in both growing seasons (Table 6-3). Squash yield in kg ha-1 was similar across treatments with mulch in the 2016 growing season. However,
TIF mulch treatment had greater yield in kg ha-1 than clear treatment in the 2015 growing season.
The squash yield in the clear treatment in 2015 may have been reduced due to limited squash plants surviving to harvest. Squash survival in all treatments was greater than 95% except for squash grown in clear mulch in 2015 season, which had 30% survival (data not shown). High soil temperatures observed with the clear mulch treatment likely contributed to limited squash survival in 2015 growing season (Figure 3). Early transitory injury to summer and winter squash with no impact on yield has been previously observed with preemergence fomesafen applications at 0.28 to 0.35 kg ai ha-1 (Peachey et al. 2012). Fomesafen has potential to be utilized for weed control in squash production.
Nutsedge Control
Evaluation date by treatment interaction was significant (P=<0.0001) for nutsedge density and dates were analyzed separately (Table 6-4). The use of any plastic mulch reduced purple nutsedge density by 60% from no mulch treatment at transplant. Treatments with TIF and
VIF reduced nutsedge density greater than 60% than no mulch treatment at harvest. TIF and VIF mulches have low fumigant vapor permeation and are more resistant to stretching, tearing, and puncturing compared with LDPE and HDPE mulches (McAvoy and Freeman 2013; Qian et al.
2011; Qin et al. 2011).
Plasticulture production with black/white mulches decreases fomesafen dissipation compared with open field production. Potential fomesafen persistence may limit grower options
93 of crops and rotations. However, squash tolerance of fomesafen may give producers an additional weed management tool for broadleaf and nutsedge control. Additional research is necessary to determine the half-life of fomesafen in Florida vegetable plasticulture production and to further identify the means of dissipation.
94 Table 6-1. Rainfall and drip irrigation volume between soil sampling dates during field experiments, 2015 and 2016, Balm, FL. Rainfall Drip irrigation Sampling perioda 2015 2016 2015 2016 ------L m-2 ------L m-2 ------Application to transplant 96 22 0 0 Transplant to harvest 156 190 1282 1089 aApplication, transplant, and harvest were 0, 19, and 103 days after treatment, respectively (2015) and 0, 22, and 83 days after treatment, respectively (2016).
95 Table 6-2. Fomesafen concentrations in soil after preemergence applications of fomesafen at 0.42 kg ai ha-1 under assorted plastic mulches from field experiments, 2015 and 2016, Balm, FL. Fomesafen concentration (DATa) 2015 2016 Plastic mulchb 0c 19 103 0 22 83 ppbd - None 150±26e (Af) 59±2 ag (B) 7±3 a (C) 176±46 (A) 39±6 a (B) 4±2 (B) Clear 176±46 (A) 67±19 a (B) 36±9 a (B) 138±18 (A) 61±12 a (B) 15±2 (B) LDPE 139±6 138±16 b 101±39 b 143±16 149±20 b 57±35 VIF 176±59 177±13 b 117±30 b 179±27 142±56 b 54±28 TIF 184±58 142±7 b 99±8 b 162±25 (A) 123±22 b (A) 22±6 (B) p-value 0.9372 0.0005 0.0086 0.8048 0.0363 0.1547 aDAT = days after treatment. bPlastic mulches are Clear (0.02 mm, Poly Expert Inc., Laval, QC Canada); LDPE (low density polyethylene mulch, 0.02 mm, FilmTech Corp., Allentown, PA); VIF (virtually impermeable film ‘Blockade’, Berry Plastics Corporation, Evansville, IN); TIF (totally impermeable film, Guardian Ag Plastics, Tampa, FL). cSoil cores were taken at application, transplant, and harvest at 0, 19, 103 days after treatment, respectively (2015) and 0, 22, 83 days after treatment, respectively (2016). dppb = parts per billion. eStandard error of the mean. fFor each year, means within rows for each treatment followed by different capital letters in parentheses are significantly different at p<0.05 using Tukey adjusted means comparisons. In 2015, p-values were 0.0045, 0.0344, 0.4813, 0.3895, and 0.1964 for none, clear, LDPE, VIF, and TIF mulch treatments, respectively. In 2016, p-values were 0.0027, 0.0043, 0.0722, 0.1813, and 0.0027 for none, clear, LDPE, VIF, and TIF mulch treatments, respectively. gMeans within columns followed by different lowercase letters are significantly different at p<0.05 using Tukey adjusted means comparison.
96 Figure 6-1. Daily average volumetric water content at 0.1 m depth under assorted plastic mulches and rainfall during the experimental period in 2015 and 2016, Balm, FL. A) 2015. B) 2016.
97 Figure 6-2. Daily average soil temperatures at 0.1 m depth under assorted plastic mulches during the experimental period in 2015 and 2016, Balm, FL. A) 2015 average temperature. B) 2015 maximum temperature. C) 2015 minimum temperature. D) 2016 average temperature. E) 2016 maximum temperature. F) 2016 minimum temperature.
98 Table 6-3. ‘Sunburst’ squash counts and yield from preemergence fomesafen applications at 0.42 kg ai ha-1 under assorted plastic mulches in field experiments, 2015 and 2016, Balm, FL. ‘Sunburst’ squash Yielda Count Plastic mulchb 2015 2016 2015 2016 kg ha-1 # ha-1 None 5,786±786c ad 27,213±2673 a 11,100±1682 a 33,974±1492 a Clear 17,716±1259 ab 59,269±2186 b 24,219±10451 ab 59,202±2712 b LDPE 30,375±8257 bc 58,597±4618 b 40,029±4303 b 63,575±4037 b VIF 28,827±3577 bc 61,018±3292 b 40,049±4985 b 60,884±2540 b TIF 36,396±3769 c 54,964±3747 b 45,747±951 b 58,529±4344 b p-value 0.0010 <0.0001 0.0017 0.0001 aYield calculations based on single row with 0.6 m spacing between plants. bPlastic mulches are Clear (0.02 mm, Poly Expert Inc., Laval, QC Canada); LDPE (low density polyethylene mulch, 0.02 mm, FilmTech Corp., Allentown, PA); VIF (virtually impermeable film ‘Blockade’, Berry Plastics Corporation, Evansville, IN); TIF (totally impermeable film, Guardian Ag Plastics, Tampa, FL). cStandard error of the mean. dMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
99 Table 6-4. Purple nutsedge density from preemergence fomesafen applications at 0.42 kg ai ha-1 under assorted plastic mulches in field experiments, 2015 and 2016, Balm, FL. Purple nutsedge density Plastic mulcha Transplantb Harvest # m-2 None 106±34c ad 121±34 a Clear 4±1 b 76±17 ab LDPE 41±14 b 71±21 ab VIF 20±8 b 40±15 b TIF 9±6 b 17±9 b p-value 0.0011 0.0154 aPlastic mulches are Clear (0.02 mm, Poly Expert Inc., Laval, QC Canada); LDPE (low density polyethylene mulch, 0.02 mm, FilmTech Corp., Allentown, PA); VIF (virtually impermeable film ‘Blockade’, Berry Plastics Corporation, Evansville, IN); TIF (totally impermeable film, Guardian Ag Plastics, Tampa, FL). bEvaluations at transplant and harvest were approximately one and three months after fomesafen application, respectively. cStandard error of the mean. dMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons.
100 CHAPTER 7 EFFECT OF INCORPORATING FOMESAFEN FOR CONTROLLING PURPLE AND YELLOW NUTSEDGE IN PLASTICULTURE
Introduction
Purple (Cyperus rotundus L.) and yellow (C. esculentus L.) nutsedge are problematic perennial weeds in plasticulture that can pierce mulch and compete with the desired crop plant.
Season-long purple and yellow nutsedge competition can reduce pepper (Capsicum annuum L.) yield greater than 70% and tomato (Solanum lycopersicum L.) yield greater than 50% (Gilreath and Santos 2004a; Morales-Payan et al. 1998; Motis et al. 2004). Producers in Florida historically relied on methyl bromide as the basis for pest management including nutsedge control (Chandler et al. 2001; Noling and Becker 1994). Alternative fumigants are generally not as effective on nutsedge as methyl bromide. For example, at 12 weeks after treatment (WAT),
Gilreath and Santos (2005b) noted a seven-fold greater purple nutsedge density in plots only treated with a combination of 82.9% 1,3-dichloropropene and 17.1% chloropicrin at 392 kg ha-1 compared to plots where methyl bromide was applied.
Preemergence herbicides including fomesafen may be applied as supplementary measures to effectively control nutsedge. Fomesafen is a diphenylether herbicide that inhibits protoporphyrinogen oxidase (Duke et al. 1991; Scalla and Matringe 1994). Fomesafen is registered in pepper and tomato production in Florida and has potential for use in other high value crops, but has not been widely adopted because of inconsistent efficacy and concern over crop tolerance. Fomesafen can control or suppress yellow nutsedge growth, but has erratic efficacy on purple nutsedge. In open field cotton production, soil-applied herbicide programs containing fomesafen controlled yellow nutsedge greater than 90% (Wilcut et al. 1997). In plasticulture production, drip applied fomesafen at 0.28 kg ai ha-1 reduced yellow nutsedge
101 punctures of mulch 89% at 8 WAT (Monday et al. 2015). Preemergence applications of fomesafen at 0.42 kg ai ha-1 controlled a mix of purple and yellow nutsedge 48% and 50% at 4
WAT in two successive years (Miller and Dittmar 2014). However, Boyd (2015) and Boyd and
Reed (2016) reported fomesafen application alone did not reduce purple nutsedge density in tomato and strawberry trials.
Florida producers apply preemergence herbicides on top of the bed after fumigation prior to laying the plastic mulch. Incorporating fomesafen may increase efficacy on nutsedge by placing the herbicide closer to tubers allowing for fomesafen to be absorbed shortly after tuber sprouting. Gilreath and Santos (2004b) reported as application depth of metolachlor at 1.13 kg ai ha-1 and napropamide at 2.25 kg ai ha-1 increased purple nutsedge density decreased. Preplant- incorporated treatments of fomesafen at 0.28 kg ai ha-1 controlled yellow nutsedge 62% compared to 40% for preemergence treatments at 4 WAT (Wilcut et al. 1991). The objective of this research was to evaluate non-incorporated fomesafen compared with irrigation and tillage incorporated fomesafen for purple and yellow nutsedge control.
Material and Methods
Greenhouse Experiment
Two greenhouse experiments were conducted at the University of Florida Gulf Coast
Research and Education Center (GCREC) in Balm, FL (27.76°N, 82.23°W), from April to July
2015, to investigate purple and yellow nutsedge tuber susceptibility to fomesafen applications.
For each experimental unit, five tubers selected for similar size per replication were planted in field soil (Myakka series fine sand; sandy, siliceous, hyperthermic Aeric Alaquods) with 1.5% organic matter and a pH of 6.5. Purple nutsedge tubers and field soil were gathered at GCREC and yellow nutsedge tubers were purchased (JB Natural Foods, S.L., Puzol, Valencia, Spain).
102 Tubers were planted at a depth of 2.5 cm in 110.3 cm2 surface area x 9.0 cm depth plastic pots in a greenhouse that averaged approximately 32/27 °C (day/night) temperature across experiments as monitored by HOBO Pro v2 data logger (Onset Computer Corporation, Bourne, MA) taking hourly measurements.
Treatments included fomesafen (Reflex 2L Liquid Herbicide, Syngenta Crop Protection,
LLC, Greensboro, NC) at 0.42 kg ai ha-1 not incorporated, irrigation incorporated, or soil tillage incorporated, and a nontreated control. The rate of fomesafen is currently labeled for use in
Florida pepper and tomato production. Treatments were applied with a CO2-pressured backpack sprayer (Bellspray Inc., Opelousa, LA) calibrated to deliver 187 L ha-1 with a single DG 9502
EVS flat-fan nozzle (TeeJet, Spraying Systems Co., Wheaton, IL) to moist soil to mimic bed formation. The water incorporated treatment was accomplished with 1.27 cm rainfall equivalent over 0.5 hours with overhead irrigation. Soil incorporated treatment was done by mixing treated soil to 2.5 cm depth. Following treatment, each pot was covered with black, virtually impermeable film (VIF) (Berry Plastics Corporation, Evansville, IN). Pots were sub-surface watered as needed to prevent soil moisture deficiencies.
Experimental design was a randomized complete block with five replications.
Emergence, shoot height, leaf number, and injury were evaluated for eight weeks. Shoot height was measured from the mulch layer to tip of tallest leaf of each shoot. Injury was evaluated on a
0 to 100 percent scale where 0 equals no visible chlorosis or stunting and 100 equals no emergence or complete desiccation. For each experimental unit, plant shoots were harvested at the soil surface at 8 WAT. Plant shoots were then oven-dried at 40 °C for 96 hours to determine dry weights. Tubers were dissected longitudinally and tested for viability using triphenyl
103 tetrazolium chloride test at 8 WAT (Akin and Shaw 2001; Miles et al. 1996). Dissected tubers were exposed to 0.1% triphenyl tetrazolium solution at 25 °C for three hours.
Field Experiment
A field experiment was conducted at GCREC, Balm, FL, from September 2015 to March
2016, to evaluate application techniques to maximize fomesafen activity in strawberry beds.
Treatments included non-incorporated fomesafen at 0.42 kg ai ha-1, irrigation incorporated, or soil tillage incorporated, and a nontreated control. Soil incorporated treatment was applied to flat
-1 ground with CO2-pressured backpack sprayer calibrated to deliver 187 L ha with three 8002VS flat-fan nozzle (TeeJet, Spraying Systems Co., Wheaton, IL) prior to bed formation on 9.2 m2 area of soil that would make up preformed bed plot. Fomesafen was then incorporated to 0.1 m depth using a tractor and rotary tiller. Raised beds were formed with bed pressing equipment with 1.2 m centers, a height of 0.3 m and bed top width of 0.7 m. Beds were fumigated with
Telone C-35 (Dow AgroSciences, Indianapolis, IN), a combination of 63.4% 1,3-dichlopropene and 34.7% chloropicrin at 336 kg ha-1. Fumigants were injected with a two-shank fumigation rig
(Kennco Manufacturing, Ruskin, FL) at a 0.2 m depth. Not incorporated and irrigation incorporated treatments were applied with a CO2-pressured backpack sprayer calibrated to deliver 187 L ha-1 with a single 8002VS flat-fan nozzle after bed formation. Water incorporated treatments were accomplished with 0.1 m rainfall equivalent with overhead irrigation using a tractor pulled sprayer over 0.1 hours. All herbicides were applied on August 27, 2015. Soil moisture measurements (FieldScout TDR 100 Soil Moisture Meter, Spectrum Technologies, Inc.,
Aurora, IL) were taken on day of application with three measurements taken in each plot to a 0.2 m depth to determine volumetric water content. Soil moisture was similar across all treatments averaging 10.2±0.3% after plastic was laid over beds. After herbicide application beds were
104 covered with VIF and fertigation was applied through a single drip tape in the center of the bed with emitters every 0.3 m and a flow rate of 0.95 L min-1 30.0 m-1 (Jain Irrigation Inc., Haines
City, FL).
Experimental design was a randomized complete block with four replications of 6.1 m plots with 1.5 m buffers between plots. Strawberry transplants of ‘Strawberry Festival’ were planted in beds of trial one month after treatment in two rows with 0.4 m spacing within rows.
Transplants received overhead irrigation during daylight hours for 14 consecutive days after transplanting to aid in establishment. Production and pest management practices were in accordance with industry standards and University of Florida/IFAS recommendations (Whitaker et al. 2015). Strawberry damage ratings were taken 2, 4, and 8 weeks after transplant (WATr) and were visually rated on a percent scale where 0 equaled no injury compared to the nontreated and 100 equaled complete desiccation. Counts and weights of strawberry marketable yield were taken biweekly. Purple nutsedge counts were taken at 0, 4, 8 and 16 WATr as an average of three densities per plot using a 0.6 m2 grid.
Statistical Analysis
Data were subjected to ANOVA at the 0.05 probability level in SAS (SAS® Institute v.
9.4, Cary, NC) using the mixed procedure with block as the random factor. Data were checked for normality and constant variance prior to analysis. Means were compared using the least squares means statement with the Tukey adjustment at p=0.05. Purple and yellow nutsedge was analyzed separately in the greenhouse experiment. Experiment by treatment interactions were not detected for greenhouse experiments and, thus, were combined. Nutsedge emergence, shoot height, leaf number, and injury in the greenhouse experiment and strawberry injury, counts, weights, and purple nutsedge counts after transplant in field experiment were collected on
105 multiple dates and were analyzed using the repeated statement. Prior to transplant the field experiment was sprayed with paraquat (Gramoxone, Syngenta Crop Protection, LLC,
Greensboro, NC) at 0.55 kg ai ha-1 for nutsedge control and the 0 WATr nutsedge density evaluation date was analyzed separately as the count was taken before paraquat application.
Results and Discussion
Greenhouse Experiment
There were no significant time by application method interactions for purple and yellow nutsedge emergence, shoot height, leaf number, and injury, and as a result the average of all evaluation dates is presented (Table 7-1 and 7-2). The affect of fomesafen on purple and yellow nutsedge was similar regardless of whether fomesafen was not incorporated, irrigation incorporated, or soil tillage incorporated. Wilcut et al. (1991) reported similar levels of yellow nutsedge control of 54% and 52% from preemergence and preplant-incorporated fomesafen treatments at 0.56 kg ai ha-1.
Purple nutsedge treated with fomesafen had less than half the dry shoot mass compared with the nontreated control. Fomesafen applications reduced purple nutsedge shoot height greater than 25% and caused greater than 60% injury. However, fomesafen treatments did not affect emergence and leaf number. Greater purple nutsedge susceptibility to fomesafen applications was observed in the greenhouse compared to prior field trials (Boyd 2015; Dittmar 2013).
All fomesafen applications decreased yellow nutsedge shoot height and leaf number greater than 25% compared with the nontreated control. Fomesafen treatments injured yellow nutsedge 78 to 82% and reduced dry shoot mass greater than 90% from the nontreated control, but did not affect emergence. Previous research has established yellow nutsedge susceptibility to
106 fomesafen (Monday et al. 2015; Wilcutt et al. 1997). Shoot suppression from fomesafen applications may reduce nutsedge vegetative reproduction and competition with crop plant.
Harvested tubers at 8 WAT had similar viability across all treatments including nontreated controls for purple (P=0.6045) and yellow (P=0.5081) nutsedge. Tubers had an average viability of 51±2% and 51±3% for purple and yellow nutsedge, respectively, across all treatments. Nontreated control viability was lower than what has been observed in previous research under conditions of the experiment (Haizel and Bennett-Lartey 1986; Webster 2003).
Akin and Shaw (2001) observed 73% and 80% viability for purple and yellow nutsedge, respectively, in tubers from the field. Preemergence and preplant-incorporated treatments of fomesafen at 0.28 kg ai ha-1 reduced the number of yellow nutsedge viable tubers greater than
90% in a potted experiment (Wilcut et al. 1991). Applications of another Protox inhibitor, sulfentrazone, reduced both purple and yellow nutsedge tuber viability in prior research (Akin and Shaw 2001; Pires da Silva et al. 2014). The lack of reduction in tuber viability from fomesafen applications while causing greater than 70% injury to nutsedge shoots may be due to a limited sample of tubers and the relatively low tuber viability in nontreated controls. Tubers may not effectively absorb fomesafen directly and have limited translocation from purple and yellow nutsedge sprouted growth.
Field Experiment
Strawberry was not injured by fomesafen applications on all evaluation dates. The harvest date by treatment interaction was not significant for berry counts (P=0.7686) and weights
(P=0.8924), and as a result total counts and yields were analyzed. Total berry counts were similar across treatments (P=0.9865) averaging 443,126±81,741 berries ha-1. Total strawberry yield was similar across treatments (P=0.9337) and averaged 7,348±1445 kg ha-1. Fomesafen safety on
107 strawberry has been previously established. McGuire and Pitts (1991) demonstrated strawberry tolerance to post-transplant applications of fomesafen at 0.28 kg ai ha-1. Boyd and Reed (2016) reported fomesafen at 0.42 and 0.84 kg ai ha-1 applied preemergence to the bed top did not cause injury or reduce yields of ‘Strawberry Festival’ and ‘WinterStar’ cultivars in the Florida production system. Fomesafen drip applied 1, 7, 15, and 30 days before transplanting at the same rates also did not reduce yields of ‘Strawberry Festival’.
Fomesafen treatments did not reduce nutsedge density compared to the nontreated control. Nutsedge counts were similar across treatments (P=0.4999) prior to paraquat application averaging 40±17 shoots m-2. The time by treatment interaction was not significant (P=0.4066) for nutsedge counts after transplant and as a result the nutsedge densities were analyzed as an average of the three counts. Nutsedge densities were similar across treatments (P=0.5014) with
32±12 shoots m-2. Applications of fomesafen at 0.42 kg ai ha-1 did not reduce purple nutsedge density compared to nontreated control. In plasticulture production, Boyd and Reed (2016) in strawberry and Boyd (2015) in tomato observed similar results.
The incorporation of fomesafen does not improve efficacy on purple and yellow nutsedge in the greenhouse or field. Fomesafen is capable of suppressing both nutsedge species for 8
WAT in the greenhouse, but does not appear to reduce tuber viability or provide consistent purple nutsedge suppression in field situations. Fomesafen may effectively be utilized for yellow nutsedge management in plasticulture production, however it seems to not be a viable option for purple nutsedge control.
108 Table 7-1. Purple nutsedge average emergence, shoot height, leaf number, injury, and dry shoot mass following fomesafen applications using multiple methods in two combined greenhouse experiments, 2015, Balm, FL. Application Method Emergence Shoot height Leaf number Injury Dry shoot massa # 5 tubers-1 cm shoot-1 # shoot-1 - % - g 5 tubers-1 Nontreated control 3 17.6 ab 6 1.07 a Not incorporated 2 12.6 b 6 66 0.39 b Irrigation incorporated 2 11.0 b 5 63 0.24 b Soil tillage incorporated 2 12.4 b 5 67 0.20 b p-value 0.1458 0.0010 0.1047 0.9277 0.0029 Emergence, shoot height, leaf number, and injury are averaged across 8 weekly evaluation dates. Emergence, injury, and dry shoot mass are presented by pot that contained five tubers. aDry shoot mass was evaluated at 8 weeks after treatment. bMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons. Product applied was Reflex 2L Liquid Herbicide (fomesafen), Syngenta Crop Protection, LLC, Greensboro, NC at 0.42 kg ai ha-1.
109 Table 7-2. Yellow nutsedge average emergence, shoot height, leaf number, injury, and dry shoot mass following fomesafen applications using multiple methods in two combined greenhouse experiments, 2015, Balm, FL. Application Method Emergence Shoot height Leaf number Injury Dry shoot massa # 5 tubers-1 cm shoot-1 # shoot-1 - % - g 5 tubers-1 Nontreated control 2 18.3 ab 7 a 0.81 a Not incorporated 1 11.8 b 5 b 78 0.05 b Irrigation incorporated 1 11.8 b 5 b 82 0.02 b Soil tillage incorporated 1 11.2 b 5 b 81 0.04 b p-value 0.0876 0.0008 0.0003 0.8683 <0.0001 Emergence, shoot height, leaf number, and injury are averaged across 8 weekly evaluation dates. Emergence, injury, and dry shoot mass are presented by pot that contained five tubers. aDry shoot mass was evaluated at 8 weeks after treatment. bMeans within columns followed by different letters are significantly different at p<0.05 using Tukey adjusted means comparisons. Product applied was Reflex 2L Liquid Herbicide (fomesafen), Syngenta Crop Protection, LLC, Greensboro, NC at 0.42 kg ai ha-1
110 CHAPTER 8 CONCLUSION
Preemergence herbicides are often required to control established weed populations in
Florida plasticulture. Utilizing herbicides with different mechanisms of action is necessary to prevent resistant weed populations in long-term management. Fomesafen is a protoporphyrinogen oxidase (Protox) inhibitor that offers an alternative mechanism of action for efficacy on nutsedge (Cyperus spp.) in small fruit and vegetable production. Inconsistent nutsedge control with fomesafen particularly with purple nutsedge (C. rotundus L.) has been observed and maximizing fomesafen efficacy is critical for its utilization in plasticulture.
Early applications of fomesafen demonstrated the ability to suppress short-term purple and yellow (C. esculentus L.) nutsedge growth in greenhouse experiments with increased efficacy occurring when the herbicide was applied as closely to tuber sprouting as possible. Field preparation can break up tuber dormancy and stimulate nutsedge growth. The time frame from soil preparation to fumigation and herbicide application may affect nutsedge growth and subsequently herbicide efficacy. Fomesafen efficacy in the field can be optimized if application is made as close to field preparation as possible.
Even at high concentrations fomesafen exposure for seven or less days had no affect on purple nutsedge tuber growth or viability without light exposure in growth chamber experiments.
Potentially tubers do not effectively absorb fomesafen directly and there is limited translocation to and from purple nutsedge growth or tubers absorb fomesafen, but there is no effect due to absence of tetrapyrrole synthesis in tuber. Light is necessary for fomesafen to be an effective weed control measure for purple nutsedge. Fomesafen inhibits Protox that catalyzes the conversion of protoporphyrinogen IX to protoporphyrin IX as part of the tetrapyrrole biosynthesis pathway. Protox inhibitors cause a rapid build up of substrates that when in the
111 presence of light, lead to lipid peroxidation resulting in cell death. However, the plasticulture system limits light exposure to fomesafen treated nutsedge until it penetrates the mulch, and rates registered for use in vegetables are unlikely to be effective. In field experiments, preemergence applications did not suppress purple nutsedge, and the incorporation of fomesafen did not improve efficacy on nutsedge in the greenhouse or field. Fomesafen is capable of suppressing both nutsedge species for eight weeks after treatment in the greenhouse, but does not appear to reduce tuber viability or provide consistent purple nutsedge suppression in field situations. The greenhouse studies had a limited amount of solitary tubers and fertilization. Herbicide application and experimentation was conducted in controlled conditions optimizing fomesafen contact and efficacy on purple nutsedge. Plasticulture practices promote purple nutsedge growth and greater density of nutsedge was observed in the field reducing fomesafen efficacy even before fertigation.
Fomesafen may effectively be utilized for yellow nutsedge management in plasticulture production, however it seems to not be a viable option for purple nutsedge control. Greater fomesafen efficacy on yellow nutsedge was observed in the greenhouse studies and has been documented in previous field research. This may be due to the growth characteristics of the two species and production practices. In the field, purple nutsedge tubers are connected in chains, whereas, yellow nutsedge tubers are not produced in chains but are generally singularly produced at the terminal end of a rhizome. Purple nutsedge growth is promoted by black polyethylene mulch. However, black mulch can reduce yellow nutsedge shoot and tuber production.
Fomesafen persistence was impacted by the plasticulture system. Production with black/white mulches decreased fomesafen dissipation compared with open field or clear mulch production with greater than twofold the fomesafen concentrations at transplant. It appears
112 sunlight and rainfall exposure had the greatest influence on fomesafen persistence as fumigation and mulch permeability did not affect dissipation. In vegetable production, fomesafen has the potential to persist at a similar concentration from day of application to harvest. The residual herbicide may limit grower options of crops and rotations. In the vegetable study evaluating fumigation affect on fomesafen, fomesafen concentrations decreased from application to transplant. This may have been the result of greater fomesafen concentrations at application compared with the study evaluating assorted plastic mulches. The majority of fomesafen dissipated throughout the growing season from the top 0.1 m in the strawberry production system with fomesafen concentration decreasing significantly at transplant when overhead and drip irrigation began to aid in establishment. Overhead irrigation and sampling next to a single drip tape in strawberry production compared with sampling in between two drip tapes in vegetable production may have led to increased fomesafen dissipation. More rapid dissipation may limit fomesafen effectiveness as a preemergence herbicide in strawberry production to time period from application to transplant. Fomesafen leaching and fate in the environment is a concern that will require assessment in Florida production.
Eggplant (Solanum melngena L.), squash (Cucurbita pepo L.), and strawberry (Fragaria
× ananassa Duch.) were tolerant of fomesafen treatments and the herbicide may be of use as an additional weed management tool in future production. Weed management with different herbicide mechanisms of action such as fomesafen could help prevent herbicide resistance, and limit the use of other herbicides. Although fomesafen does not appear to be a feasible alternative for purple nutsedge control, the herbicide may further be used in plasticulture production for yellow nutsedge, broadleaf, and grass weed management as efficacy and tolerance is established in more crop species.
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124 BIOGRAPHICAL SKETCH
Thomas Reed grew up in Seymour, WI where he graduated from Seymour Community
High School in 2007. He then attended the University of Wisconsin where he received his
Bachelor of Science degree in biology and a certificate in environmental studies in 2010.
Thomas achieved his Master of Science degree in crop and soil sciences at the University of
Georgia in 2013. Thomas continued his graduate work at the University of Florida where he earned his Ph.D. in horticultural sciences in 2017.
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