Source: UNIVERSITY OF FLORIDA submitted to
Sponsoring Institution
State Agricultural Experiment Station
Project Status
Funding Source
Reporting Frequency
Accession No.
Grant No.
Project No.
Proposal No.
Multistate No.
Program Code
Project Start Date
Oct 1, 2001
Project End Date
Sep 30, 2007
Grant Year
Project Director
Chase, C. A.
Recipient Organization
Performing Department
Non Technical Summary
The vegetable industry is facing weed management crises due to the impending loss of methyl bromide, and legislation that will limit the re-registration of many pesticides including herbicides. Studies of weed biology, herbicide efficacy, herbicide selectivity, and herbicide resistance will generate data to develop alternative weed management systems, extend the efficient use of herbicides to new crops/situations, and promote appropriate and sustainable use of herbicides.
Animal Health Component
Research Effort Categories

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
Goals / Objectives
The overall objective is to utilize information generated by biological, physiological, biochemical, and genetic studies of crops and weeds to improve weed management strategies for horticultural crops. The specific objectives are: (I) To investigate weed/crop interactions such as competition and allelopathy to optimize herbicide usage and improve weed management. This will include studies that evaluate the effects of increasing densities of selected weeds on the growth and yield of specific vegetable crops, and critical period studies to determine appropriate times for weed control in specific crops. (II) To screen herbicides to generate data for establishing herbicide tolerances and for issuing herbicide labels. Studies will focus on evaluating the tolerance of specific vegetable crops to potential herbicides, the efficacy of specific herbicides on weed species, and investigate the application timing of herbicides on crop tolerance and weed control. (III) To characterize biochemical bases of herbicide selectivity: (1) to purify acetolactate synthase from tomato and pepper and characterize the kinetics of the respective enzymes, (2) to determine the rate of rimsulfuron breakdown in vivo, (3) to identify rimsulfuron metabolites, (4) to explore the effects of insecticides on rimsulfuron metabolism, (5) to characterize the activities of enzymes implicated in rimsulfuron metabolism in tomato. (IV) To elucidate mechanisms of herbicide resistance in crops and weeds: (1) to further characterize impaired electron transport in paraquat-resistant Solanum americanum, (2) to explore paraquat metabolism as a secondary mechanism of resistance, (3) to elucidate the mechanism of paraquat resistance in Eleusine indica.
Project Methods
(I) Studies of weed/crop interference will employ techniques such as additive studies to determine the number of weeds that will reduce crop yield and quality, and critical period studies to determine the critical period of interference or the time the crop must be kept weed free to prevent more than 5% yield loss. (II) Trials to assess herbicide efficacy and crop tolerance will be conducted. (III) Enzyme systems involved in sulfonylurea selectivity will be assessed. Acetolactate synthase will be partially purified from leaves of tomato and pepper seedlings and used to determine kinetic constants for the substrate and cosubstrates and inhibitor constants for rimsulfuron and halosulfuron. Rates of rimsulfuron breakdown in tomato, pepper, and other solanaceous crops and weeds will be determined. Leaf and root tissues will be incubated for various periods of time with radiolabeled herbicide, then extracted in an appropriate extraction medium. Chromatography and autoradiography will be used to separate and distinguish metabolites from radiolabeled herbicide. The effect of insecticides on rimsulfuron metabolism in tomato will be evaluated in greenhouse trials. Potential involvement of cytochrome P450 monooxygenases (P450s) in rimsulfuron metabolism will be examined in isolated microsomes from tomato leaves. Kinetic constants for rimsulfuron and co-substate NADPH will be calculated. The product of the reaction will be separated by HPLC and verified by mass spectrometry. P450 activity will be characterized by studying the effect of known inhibitors. Substrate specificity will be examined by using a number of radiolabeled substrates and xenobiotics. Glucose conjugation of rimsulfuron by UDP-glucosyltransferases will be investigated in tomato. Depending on the metabolite profile other enzymes will be characterized. (IV) The efficiency of electron transport in isolated thylakoids of paraquat-resistant (R) and -sensitive (S) biotypes of Solanum americanum will be compared to determine the cause of restricted development of oxidative stress in the R biotype. Paraquat metabolism will be examined as a potential secondary mechanism of resistance in S. americanum. R and S plants, treated with C-14 paraquat for varying intervals, will be harvested and extracted with appropriate solvents to obtain parent compound and metabolites. C-14 paraquat and possible metabolites in the concentrated extract will be separated by chromatography and identified by comparison with standards of paraquat and related compounds, and quantified. Isogenic lines of the R and S biotypes will be developed for genetic characterization of paraquat resistance in S. americanum. The elucidation of the mechanism of paraquat resistance in Eleusine indica will involve comparison of absorption, translocation, and metabolism of C-14 paraquat in R and S biotypes; comparison of the kinetics of paraquat movement to the site of action in the R and S biotypes, and activity at the site of action; assessment of electron transport and capacities for production of active oxygen species; and comparison of constitutive levels of protective enzymes and antioxidants.

Progress 10/01/01 to 09/30/07

OUTPUTS: Several graduate students were trained while conducting the research described in this project. All but one of these students continue to work in agriculture or is pursuing a doctoral degree in an agricultural science. The results of these studies were reported at conferences such as the annual meetings of the Southern Weed Science Society and the Weed Science Society of America and published in refereed journals. PARTICIPANTS: Much of the work reported was conducted by graduate students advised by Drs. Chase, Stall, and Rathinasabapathi. At least two undergraduate students received summer undergraduate research internships to work on aspects of this project. TARGET AUDIENCES: The target audiences were students at the University of Florida, extension professionals, and our scientific peers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Important information has been generated on the limitations of 1,3-dichloropropene drip applied through one irrigation line in sandy soils. Leguminous cover crops (sunn hemp, Iron Clay cowpea, and velvet bean) were evaluated to determine whether their effectiveness for yellow nutsedge and smooth pigweed suppression was due to inherently greater competitiveness than the weeds. This was not generally the case and so ensuring that cover crops are planted at appropriate densities is extremely critical to ensure effectiveness for weed suppression. It was also determined that higher densities of sunn hemp and velvet bean are needed for smooth pigweed suppression when the weed density is increased from 5 plants per m2 to 15 plants per m2. Foliar extracts from the leguminous cover crops: sunn hemp, Iron Clay cowpea, and velvet bean were found to be phytotoxic. This suggests that weed suppression by these cover crops could be due to allelopathy in addition to competition and the changes in soil microclimate that can have adverse effects on weed germination. Hydramulch, a paper-like material applied as a slurry consisting of cotton waste, newsprint, gypsum and a proprietary adhesive, was tested as a biodegradable alternative to polyethylene mulch. Hydramulch resulted in cooler soils than polyethylene, allowed the penetration of water from rainfall, and suppressed broadleaf weeds and grasses. However, since purple nutsedge readily penetrated hydramulch, it is only suitable for use at sites with little or no nutsedge pressure. Shoot growth and marketable yields of bell pepper and muskmelons were lower than with polyethylene mulch. Leacheates from wood chips of southern red cedar and southern magnolia were shown to suppress weed germination in potted crepe myrtle plants as effectively as a commercial herbicide, without inhibiting crepe myrtle growth. Studies were conducted to explain the differences in sensitivity of tomato and pepper to the sulfonylurea herbicides rimsulfuron and halosulfuron. The use of an inhibitor of cytochrome P450 enzymes provided evidence of differences in sulfonylurea metabolism in these two species. In studies of interference between American black nightshade and watermelon in polyethylene-mulched and nonmulched (bare ground) yield declines of 50 and 80%, respectively could be incurred with as few as 2 American black nightshade plants per m2. In a replacement series study cucumber was found to be more competitive than smooth pigweed and livid amaranth three times more competitive than smooth pigweed or livid amaranth. However, in field studies of the effect of season-long interference of smooth pigweed or livid amaranth on the shoot dry weight and fruit yield of cucumber, smooth pigweed or livid amaranth densities as low as 1 to 2 weeds per m2 caused a 10% yield reduction in cucumber. The biological threshold of smooth pigweed or livid amaranth with cucumber was determined to between 6 to 8 weeds per m2.


  • Gilbert, C.A., W.M. Stall, C.A. Chase and R. Charudattan. 2008. Season long interference of American black nightshade with watermelon. Weed Technology 22:186-189.

Progress 10/01/05 to 09/30/06

Additive studies were conducted to investigate the interference of American black nightshade (nightshade) with watermelon at 2 locations. In 2005, 2 nightshade plants/m2 reduced watermelon yield 100% when grown on bare ground. When grown with plastic mulch, watermelon yield decreased by 80% and 98% at 2 and 8 nightshade plants/m2, respectively. In 2006, nightshade reduced watermelon yield by 68% and 93% at 2 and 8 plants/m2, respectively, on bare ground. With plastic mulch, yield loss from interference of 2 nightshade/m2 was 54% increasing to a loss of 85% with 8 nightshade/m2. Thus, nightshade is very competitive with watermelon and yield loss is greater when watermelon is grown on bare ground than when grown in mulch culture. The effect of living mulches (LM) on weed suppression and broccoli growth and yield were evaluated in North Central Florida (NCF) and North Florida (NF) using organic production methods. 'Florida 401' (FL401) rye, 'Wrens Abruzzi' (WA) rye, black oat, and annual ryegrass were either mowed or not and compared with weedy and weed-free controls. LM biomass was highest with FL401 rye, intermediate with black oat and WA rye, and lowest with ryegrass. Weed infestation was greatest with the weedy control. In NCF, ryegrass decreased weed biomass by 21% compared with ~45% by the other LM with no differences due to mowing. However, at NF mowed LM and the weedy control had similar amounts of weed biomass; whereas unmowed LM had 30-40% less weed biomass than the weedy control. At both locations, broccoli was tallest with the weed-free control, intermediate with the cover crops, and shortest with the weedy control. Ryegrass and the weedy control suppressed marketable broccoli weight by 24%; however, greater decrease in marketable weight (39-43%) occurred with FL401 rye, WA rye, and black oat. Mowing of LM had no effect on broccoli growth or yield. The efficacy of woodchip mulches for weed suppression in nursery containers and whether their use can reduce the need for a chemical herbicide were investigated. In laboratory bioassays, water leachates of red cedar and magnolia wood chips were highly inhibitory to germinating lettuce seedlings. Leachate from wood chips of oriental arborvitae and Leyland cypress reduced growth of lettuce seedlings but were less effective than that of red cedar. In greenhouse tests, red cedar and magnolia woodchip mulches significantly inhibited the germination of redroot pigweed and large crabgrass. In a field trial, nursery containers with crape myrtle plants were sown with hairy crabgrass and redroot pigweed seeds, mulched with red cedar or magnolia wood chips and compared to plants without mulch and plants treated with a herbicide (Snapshot-a mixture of isoxaben and trifluralin). Red cedar and magnolia wood chips were as effective as Snapshot in suppressing weed growth. Woodchip mulches did not inhibit crape myrtle growth. In a field trial using containered dogwood plants sown with large crabgrass and redroot pigweed, red cedar woodchip mulch suppressed weeds most effectively when combined with a low dose of Snapshot.

This work demonstrates the need for effective strategies to control American black nightshade in watermelon production. Organic growers and conventional growers interested in cultural methods of weed suppression will understand that the benefit of weed suppression offered by a living mulch can be offset by the competition between the living mulch and the cash crop. The potential of red cedar and magnolia wood chip mulches for organic and/or integrated weed management in the nursery industry was demonstrated.


  • Berry, A. D., W. M. Stall, B. Rathinasabapathi, G. E MacDonald and R. Charudattan. 2006. Smooth Pigweed (Amaranthus hybridus L.) and livid amaranth (Amaranthus lividus) interference with cucumber (Cucumis sativus). Weed Technol. 20:227-231.
  • Chase, C.A. and M. Adler. 2006. Phytotoxicity of foliar extracts and residues of leguminous summer cover crops. WSSA Abstracts 46:82-83.
  • Chase, C.A., O.S. Mbuya, and D.D. Treadwell. 2006. Living mulches for weed suppression and enhanced water infiltration in fall broccoli. HortScience 41:998.
  • Chase, C.A., W.M Stall, E.H. Simonne, R.C. Hochmuth, M.D. Dukes, and A.W. Weiss. 2006. Nutsedge control with drip-applied 1,3-dichloropropene plus chloropicrin in a sandy soil. HortTechnology 16(4):641-648.
  • Gilreath, J.P., B.M. Santos, C.A. Chase, and S.J. Locascio. 2006. Influence of soil fumigation on 2,4-D and dicamba carryover in fresh market tomato. Crop Protection 26:1095-1100.
  • Linares, J., J. Scholberg, C. Chase, R. McSorley, and J. Ferguson. 2006. Integrative approaches for weed management in organic citrus orchards. HortScience 41:998.
  • Scholberg, J.M.S., C.A. Chase, J.C. Linares, R.M. McSorley, and J.J. Ferguson. 2006. Integrative approaches for weed management in organic citrus orchards. HortScience 41:949.
  • Scholberg, J., J. Linares, and C. Chase. 2006. Cover Me! Florida Grower, Issue 9, page 14.
  • Warnick, J.P., C.A. Chase, E.N. Rosskopf., J.M. Scholberg, E.H Simonne, R.L. Koenig, and N.E. Roe. 2006. Hydramulch for Muskmelon and Bell Pepper Crop Production Systems. Journal of Vegetable Science 12(2):39-55.
  • Warnick, J.P., C.A. Chase, E.N. Rosskopf, E.H. Simonne, J.M. Scholberg, R.L. Koenig, and N.E. Roe. 2006. Weed suppression with hydramulch, a biodegradable liquid paper mulch in development. Renewable Agriculture and Food Systems 21(4):216-223.

Progress 10/01/04 to 09/30/05

In spring and fall 2004 nonsynthetic herbicides Alldown, Ground Force, Matran 2 and Xpress were evaluated on 2 to 4-in tall weeds in comparison with flame weeding. Flaming was more effective than the nonsynthetic herbicides. In spring, weed canopy decreased from 93 % with the nontreated check to 81 % with Alldown and 76 % with Matran 2. However, weed canopy with flaming was 24 %. There was no difference in biomass among the treatments. In fall, only flaming resulted in significantly lower weed canopy and biomass than the nontreated check. In both spring and fall, as number of applications increased weed canopy decreased in a linear manner. A concomitant linear decline of weed biomass was also observed in fall. However, no significant decrease in biomass occurred in spring. Cyperus globulosus, Paspalum notatum, Digitaria ciliaris, Commelina benghalensis, Richardia scabra, and Sida sp. were all susceptible to flaming; however, sensitivity to the nonsynthetic herbicides varied with species. C. globulosus and the grasses were not well controlled by the herbicides. C. benghalensis was more sensitive to the citric acid herbicides and broadleaf species were more sensitive to the essential oil herbicides. Twelve winter cover crops were evaluated for use as living mulches in fall 2004: black oats (Avena strigosa cv. Soilsaver), annual ryegrass (Lolium multiflorum cv. Gulf), rye (Secale cereale cv. Wrens Abruzzi), hard fescue (Festuca longifolia cv. Oxford), white clover (Trifolium repens cvs. Dutch white and New Zealand white), berseem clover (T. alexandrinum cv. Bigbee), crimson clover (T. incarnatum cv. Dixie), subterranean clover (T. subterraneum cv. Mt. Barker), arrowleaf clover (T. vesiculosum cv. Yuchi), a barrel medic (Medicago trunculata cv. Parabinga), and a disc x strand medic (M. tornata xM. littoralis cv. Toreador). Black oats, rye, and annual ryegrass established quickly and suppressed winter annual weeds and appear to be the best living mulch candidates. Canopy development in the other species was poor. Exposure to wheel traffic or mowing resulted in lower biomass at some harvests, but black oats, rye and ryegrass did not succumb to these treatments. Earlier we found that woodchip mulches from certain tree species will be useful for weed suppression. These results were extended to weed control in nursery containers. Woodchip mulches from red cedar and magnolia were effective in suppressing monocot and dicot weeds in crape myrtle nursery containers. The significance of this finding is that it may become possible to reduce the use of chemical herbicides by using recycled agricultural and forestry waste. Physiological and biochemical work focused on beta-alanine synthesis, a potential herbicide target, has led to novel findings about the potential use of this pathway for improving high temperature tolerance of crop plants.

Flame weeding, living mulches, and allelopathic materials may be useful for managing weeds in organic and sustainable conventional production systems contributing to a reduction in use of synthetic herbicides and decreasing adverse human and environmental effects. Potential benefits of understanding beta-alanine synthesis are: a new target site for herbicides and improving high temperature tolerance in crop plants.


  • Chase, C.A. and Mbuya, O.S. 2005. Cool-season living mulches for Florida. HortScience 40:1024.
  • Chase, C.A., Scholberg, J.M., and MacDonald, G.E. 2005. Comparison of nonsynthetic herbicides and flaming for use in organic systems. Proc. Southern Weed Science Society 58:154.
  • Chase, C.A., Dukes, M.D., Hochmuth, R.C., Simonne, E.H., Stall, W.M., and Weiss, A.W. 2004. Optimizing Inline application for effective pest management and crop nutrition. HortScience 39:658.
  • Collins, A.S., Chase, C.A., Stall, W.M., and Hutchinson, C.M. 2004. Cover crops for weed suppression. Proc. Florida Weed Science Society.
  • Collins, A.S., Chase, C.A., Stall, W.M., and Hutchinson, C.M. 2004. Competitiveness of three leguminous cover crops. WSSA Abstracts 44: 75. Weed Science Society of America.
  • Collins, A.S., Chase, C.A., Stall, W.M., and Hutchinson, C.M. 2004. Suppressing weeds during summer fallow with leguminous cover crops. Proc. Southern Weed Science Society 57:203.
  • Fayiga, A.O., Ma, L.Q., Santos, J., Rathinasabapathi, B., Stamps, B., and Littell, R.C. 2005. Effects of arsenic species and concentrations on arsenic accumulation by different fern species in a hydroponic system. Int. J. Phytoremediation (in press).
  • Ferguson, J.J. and Chase, C.A. 2004. Status and preliminary research on non-synthetic herbicides for organic production. EDIS Factsheet HS1003.
  • Fouad, W.M. and Rathinasabapathi, B. 2005. Expression of bacterial L-aspartate-alpha-decarboxylase in tobacco increases beta-alanine and pantothenate levels and improves thermotolerance. Plant Molecular Biology (in press).
  • Rathinasabapathi, B. and Raman, S.B. 2005. Exogenous supply of pantoyl lactone to excised leaves increases their pantothenate levels. Annals of Botany 95:1033-1037.
  • Rathinasabapathi, B., Ferguson, J., and Gal, M. 2005. Evaluation of allelopathic potential of wood chips for weed suppression in horticultural production systems. HortScience 40:711-713.
  • Singh, N., Ma, L.Q., Srivastava, M., and Rathinasabapathi, B. 2005. Metabolic adaptations to arsenic-induced oxidative stress in Pteris vittata L. and Pteris ensiformis L. Plant Science (in press).

Progress 10/01/03 to 09/30/04

Application of the soil fumigant InLine (1,3-dichloropropene + chloropicrin) via drip irrigation requires a considerable volume of water as a carrier. Studies were conducted to evaluate how such volumes of water would affect preplant soil-applied materials. Granular fertilizer and the herbicides s-metolachlor, napropamide, and oxyfluorfen were applied prior to covering beds with polyethylene mulch. Either 115, 139 or 173 gal water per 100 linear bed feet were applied to beds via drip tubing. Nitrate-N, ammonium-N, phosphorus, and potassium movement within the soil differed in the two experiments conducted. Nitrate-N was the most mobile nutrient and the most likely to contaminate ground water. If the use of InLine is adopted in plasticulture production systems, controlled-release fertilizers can be used or post-plant nitrate-N fertigation is recommended. The soil applied herbicides were also subject to leaching, napropamide more so than s-metolachlor and oxyfluorfen. Although napropamide is the only herbicide likely to result in groundwater contamination, the movement of s-metolachlor and oxyfluorfen that occurred would considerably reduce their efficacy. The efficacy of weed control with three nonsynthetic, postemergence, contact herbicides (Alldown, Matran 2, and Xpress) was compared with that of corn gluten meal applied preemergence, and flame weeding. The most effective treatment on mature weeds was flame weeding, which gave 97 % control 1 week after application (WAA) but only 79 % by 3 WAA. Alldown and a 20 % concentration of Matran 2, provided better than 70 % weed control within the first week, but decreased to less than 60 % by 3 WAA. Control ranged from 68 to 75 % 5 WAA with corn gluten meal applied preemergence, and with 20 % Matran 2 and flame weeding treatments of recently emerged weeds. Control with Xpress was inconsistent, but could likely be improved by closer attention to product agitation before dispensing as well as proper agitation of the spray during application. Investigations were focused on understanding enzyme systems involved in plant nitrogen metabolism that could be potential targets for herbicides. Pantothenate synthesis in plants was characterized by supplying exogenous putative precursors to excised leaves. It was concluded that pantothenate synthesis in plants may not be limited by beta-alanine but by the availability of d-pantoate. A mutant impaired in pantothenate synthesis in thale cress was characterized. Wood chips are commonly used for weed control in horticultural crops. Since wood chips with allelochemicals can potentially be more effective for weed suppression, wood chips from various woody perennials were screened in laboratory studies. In neem and red cedar, leaves had more allelopathic potential than wood. Allelopathic activities of red cedar wood chips were evaluated in a greenhouse experiment. Florida beggarweed was significantly inhibited by the red cedar wood chip mulch.

Identification of novel potential target sites for herbicides, assessing the potential effects of proposed pest management strategies such as nutsedge management with the soil fumigant InLine, and evaluating nonsynthetic herbicides and allelopathic materials as mulches may result in more sustainable approaches to weed management in conventional horticultural production and increased options for organic producers while limiting negative effects on human and environmental health.


  • Santos, B.M., Dusky, J.A., Stall, W.M., and Gilreath, J.P. 2004. Influence of common lambsquarters (Chenopodium album) densities and phosphorus fertilization on lettuce. Crop Protection 23:173-176.
  • Santos, B.M., Dusky, J.A., Stall, W.M., Bewick, T.A., Shilling, D.G., and Gilreath, J.P. 2004. Phosphorus absorption in lettuce, smooth pigweed (Amaranthus hybridus), and common purslane (Portulaca oleracea) mixtures. Weed Science 52(3):389-394.
  • Santos, B.M., Dusky, J.A., Stall, W.M., Bewick, T.A., and Shilling, D.G. 2004. Mechanisms of interference of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) on lettuce as influenced by phosphorus fertility. Weed Science 52:78-82.
  • Buker, R.S., Rathinasabapathi, B., Stall, W.M., MacDonald G., and S.M. Olson. 2004. Physiological basis for differential tolerance of tomato and pepper to rimsulfuron and halosulfuron: site of action study. Weed Science 52(2):201-205.
  • Chase, C.A., Scholberg, J.M., and MacDonald, G.E. 2004. Preliminary evaluation of nonsynthetic herbicides for weed management in organic orange production. Proc. Fla. State Hort. Soc. 117 (In Press).
  • Fayiga, A., Ma, L.Q., Cao, X., Rathinasabapathi, B. 2004. Effects of heavy metals on growth and arsenic accumulation in the arsenic hyperaccumulator Pteris vittata. Environmental pollution 132:289-296.
  • Morales-Payan, J.P. and Stall, W.M. 2003. Papaya (Carica papaya) response to foliar treatments with organic complexes of peptides and amino acids. Proc. Fla. State Hort. Soc. 116:30-32.
  • Morales-Payan, J.P. and Stall W.M. 2003. Effect of substrates, boron, and humic acid on the growth of papaya transplants. Proc. Fla. State Hort. Soc. 116:28-30.
  • Morales-Payan, J.P. and Stall, W.M. 2003. Density and time of emergence of purple nutsedge (Cyperus rotundus L.) effects on bell pepper (Capsicum annuum L.). Proc. Fla. State Hort. Soc. 116:75-77.
  • Santos, B.M., Dusky, J.A., Stall, W.M., Bewick, T.A., Shilling, D.G. 2004. Influence of method of phosphorus application on smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) interference in lettuce. Weed Science 52(5): 797-801.
  • Warnick, J.P. 2004. Hydramulch for weed control in melon and pepper production. MS Thesis, University of Florida.
  • Warnick, J.P., Chase, C.A., Simonne, E.H., Scholberg, J.M., and Rosskopf., E.N. 2004. Hydramulch for weed control in melon and pepper production. Proc. Southern Weed Science Society 57:144.
  • Morales-Payan, J.P., Stall, W.M., Shilling, D.G., Dusky, J.A. Bewick, T.A. and Charudattan R. 2003. Initial weed-free period and subsequent yellow nutsedge population density affect tomato yield. Proc. Fla. State Hort. Soc. 116:73-75.
  • Myers, L., Wang, K.-H., McSorley, R. and Chase, C. 2004. Investigations of weeds as reservoirs of plant-parasitic nematodes in agricultural systems. Proceedings 26th Annual Conservation Tillage Conference for Sustainable Agriculture. Pp 258-267.
  • Raman, S.B., and Rathinasabapathi, B. 2004. Pantothenate synthesis in plants. Plant Science 167:961-968.
  • Santos, B. M., Dusky, J.A., Stall, W.M., and Gilreath, J.P. 2004. Effect of phosphorus fertilization on common lambsquarters (Chenopodium album) duration of interference in lettuce (Lactuca sativa). Weed Technology 18:152-156.

Progress 10/01/02 to 10/01/03

Techniques to improve nutsedge control with 1,3-dichloropropene + chloropicrin applied as 35 gal per acre of InLine via a single drip-irrigation line were evaluated. Widths of beds were varied: 24, 28, 32, or 36 in; the drip line was installed at the soil surface or buried 6-in; and either a standard low density polyethylene (LDPE) film or a virtually impermeable film (VIF) was used as mulch. Nutsedge densities at bed centers were lower than at shoulders. Narrow bed-widths did not eliminate nutsedge emergence on bed shoulders. Nutsedge densities were initially low with VIF, but suppression did not persist. Nutsedge control with InLine was unsatisfactory indicating that tubers that occur outside of the zone wetted by InLine were not killed and allowed reinfestation of beds. The impact of the large volumes of water used to apply InLine on soil-applied herbicides and fertilizers was also assessed. Hydramulch (HM), made primarily with cotton waste, newspaper, gypsum, and water, is a paper mulch that is applied as a slurry to the soil surface. HM was evaluated for weed suppression in sustainable systems and appears to be less susceptible to blow off when applied to beds than standard paper mulch and did not blow off at all when applied to flat planting surfaces. When applied at 4 cm thick it suppressed broadleaf and grass weeds more effectively than at 2 cm. HM was readily penetrated by purple nutsedge. Surveys of common weeds and associated plant parasitic nematodes were conducted at two organic farms and two conventional farming systems in order to assess the importance of weeds as reservoirs of plant parasitic nematodes. Purple nutsedge, pigweed, lambsquarters, and crabgrass were the weeds frequently encountered. Root-knot nematode was the major plant parasitic nematode frequently found in association with these weeds in relatively high numbers. The results suggest that economically important plant parasitic nematodes cannot be effectively managed unless weeds are also managed. The physiological basis for the differential tolerance of pepper and tomato toward sulfonylurea herbicides was examined. The hypothesis that tomato is tolerant because of its greater ability to metabolize sulfonylurea herbicides was tested. Radiolabeled herbicides were supplied to tomato and pepper seedlings and metabolites were isolated and separated by thin layer chromatography. Autoradiography of the chromatography plates was used to identify the radiolabeled metabolites of rimsulfuron. The metabolites were significantly more per unit of tomato tissue than in pepper. Some metabolites were identified using mass spectrometry. The identity of the herbicide metabolites suggested the possible role of P450-type enzymes in sulfonylurea metabolism. Wood chips are commonly used for weed control in horticultural crops. Since wood chips with allelochemicals can potentially be more effective for weed suppression, a program was initiated to screen wood chips from a number of tree species for water-soluble allelochemicals. So far, 15 species of trees naturally found in Florida were evaluated and five species were identified with high levels of allelopathic activity.

Studies with InLine indicate that application methods that permit the entire width of the bed to be wetted are needed for adequate nutsedge control. A greater understanding of the mechanism of selectivity of sulfonylurea herbicides in tomato continues to emerge. Information is being generated on alternative and sustainable methods of weed control such as biodegradable and allelopathic mulches, and host weeds that need to be controlled during fallow and cover crops to suppress plant pathogenic nematodes.


  • Berry, A.D. 2002. Smooth pigweed (Amaranthus hybridus L.) and livid amaranth (Amaranthus lividus L.) interference with cucumber (Cucumis sativus L.). MS thesis, University of Florida.
  • Buker III, R.S., Stall, W.M., Olson,S.M. and Shilling, D.G. 2003. Season-long interference of yellow nutsedge (Cyperus esculentus) with direct-seeded and transplanted watermelon (Citrullus lanatus). Weed Technology 17 (4):751-754.
  • Ferguson, J.J., Rathinasabapathi, B., and Reichenbach, R. 2003. Evaluation of allelopathic potential of wood chips used for weed suppression in sustainable crop production systems. HortScience 38:770 (Abstract).
  • Ferguson, J.J. and Rathinasabapathi, B. 2003. Allelopathy: How plants suppress other plants. University of Florida IFAS Extension publication number HS944. (EDIS
  • Morales-Payan, JP; Stall, WM; Shilling, DG; Charudattan, R; Dusky, JA; Bewick, TA. 2003. Above- and below-ground interference of purple and yellow nutsedge (Cyperus spp.) with tomato. Weed Science 51 (2): 181-185.
  • Motis, TN; Locascio, SJ; Gilreath, JP; Stall, WM. 2003. Season-long interference of yellow nutsedge (Cyperus esculentus) with polyethylene-mulched bell pepper (Capsicum annuum). Weed Technology, 17 (3): 543-549.

Progress 10/01/01 to 10/01/02

Studies are being undertaken to develop recommendations for the use of a formulation of 1,3-dichloropropene plus chloropicrin (InLine) developed for application through the drip-irrigation system. This summer, an experiment was conducted to compare nutsedge control with InLine on beds 61, 71, 81, and 91 cm-wide and mulched with either 0.035 mm virtually impermeable film (VIF) or 0.019 mm high density polyethylene (HDPE). HDPE was more permeable to InLine than VIF. One day after application, the soil gas concentration at the center of the beds was approximately 250 ppm and 500 ppm with HDPE and VIF, respectively. Soil gas declined to 20 ppm by 4 and 10 days after treatment. By 2 weeks after treatment (WAT) fewer than 4 nutsedge plants had emerged in the centers of beds mulched with HDPE, while no nutsedge was apparent with VIF. However, nutsedge emerged along bed shoulders of both film types with a greater density occurring with HDPE. Nutsedge densities were also assessed at 4, 8 and 12 WAT and will be reported subsequently. The physiological basis for the differential tolerance of pepper and tomato toward sulfonylurea herbicides was examined. During 2002, we tested the hypothesis that tomato is tolerant to sulfonylurea herbicides because of poor uptake and translocation of the herbicidal compound by tomato compared to pepper. Radiotracer experiments were conducted to measure rates of root and foliar uptake of sulfonylurea herbicides, rimsulfuron and halosulfuron in tomato and pepper seedlings. Translocation of the labeled herbicide or its degradation products, was monitored using autoradiography of pressed plant specimens following the supply of the compound. The results indicated that tomato and pepper did not differ significantly in both the uptake and translocation of labeled herbicide or its degradation products. This study, together with our previous results on their properties of the target enzyme in both these species, suggested that tomato's tolerance to sulfonylurea herbicides is due to metabolism of sulfonylurea herbicides by an enzyme system. Future experiments will focus on identifying sulfonylurea herbicide metabolism in tomato and pepper.

The InLine studies may result in recommendations to enhance the efficacy of the soil fumigant against nutsedges and prevent ground-water contamination, while ensuring adequate nutrition of the crop and effective weed control with soil-applied herbicides. The studies on sulfonylurea herbicides have contributed to greater understanding of herbicide selectivity in tomato and pepper.


  • Morales-Payan, J.P., W.M. Stall, and R. Charudattan. 2001. Effect of purple nutsedge density and size of basil transplant on basil yield. Soil Crop Sci. Soc. Florida Proc. 61:30-32.
  • Berry, A., W.M. Stall, B. Rathinasabapathi, G.E. MacDonald, and R. Charudattan. 2001. Competition of smooth (Amaranthus hybridus) and livid (A. lividus) amaranth with cucumber (Cucumis sativus). Proc. Fla. State Hort. Soc. 114:272-274.
  • Buker III, R.S., S.T. Steed, and W.M. Stall. 2002. Confirmation and control of a paraquat-tolerant goosegrass (Eleusine indica) biotype. Weed Technology 16:309-313.
  • Buker, R.S. 2002. Differential tolerance of tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum L.) to rimsulfuron and halosulfuron herbicides. PhD dissertation, University of Florida, Gainesville.

Progress 10/01/00 to 10/01/01

Yellow and purple nutsedge are major weed problems in watermelon production. Six yellow nutsedge plants per square meter will reduce watermelon yield by 10%. At present, there are no labeled herbicides that will control nutsedge in watermelon production. Halosulfuron will control both nutsedge species and is expected to receive a tolerance in the 'melon' subgroup through the IR-4 program in 2002. Previous research has shown that the timing of application is important to reduce early yield loss. In seeded watermelon, application must be made three weeks after emergence. Previous trials with transplanted watermelon indicated that 'weeks after transplanting' could not be used as a criterion for application timing. In examining the data, however, it was thought that runner length could be used as an alternative indicator. Trials were established at two locations and halosulfuron was applied at the following runner lengths: 0-6, 6-12, 12-18, 18-24, and 24-26 inches. Results indicated that no early yield loss occurred when the runners were 12 to 24 inches long at halosulfuron application. Halosulfuron application to 12-24 inch runners would correspond with the critical period of nutsedge interference in watermelon and provide very beneficial nutsedge control without causing any yield loss. Grant funding was obtained for integrated pest management studies with summer cover crops and herbicides. A graduate student was recruited for the project and joined the program in August. Her research is focused on evaluating weed/cover crop interference as part of an initiative to develop a biologically-based sustainable tomato production system that does not include methyl bromide. Work is also ongoing to locate the lesion in electron transport that restricts the development of oxidative stress in paraquat-resistant American black nightshade. Differential herbicide tolerance of tomato and pepper to sulfonylurea herbicides was investigated. Although both tomato and pepper are members of the Solanaceae family, tomato is tolerant to rimsulfuron and halosulfuron while pepper is sensitive. The metabolic target for sulfonylurea herbicides is acetolactate synthase, the first enzyme in branched-chain amino acid biosynthesis. During 2001, we investigated whether differential tolerance to sulfonylurea herbicides between tomato and pepper is due to differences in their acetolactate synthase. Kinetic characterization of this enzyme extracted from leaves of tomato and of pepper was completed. Both substrate and inhibitor interactions were considered. The studies revealed that properties of acetolactate synthase do not differ between tomato and pepper. This implies that other mechanisms are responsible for the observed tolerance differences. This work has not yet been submitted for publication but forms part of a graduate student's thesis work.

Halosulfuron will give growers the ability to control nutsedges in watermelon. Work on weed/cover crop interference will contribute to a more sustainable approach to pest management in vegetable crops. The study of differential tolerance of tomato and pepper to sulfonylurea herbicides will provide an improved understanding of the biochemical basis of herbicide selectivity.


  • Gilreath, J.P., Chase, C.A. and Locascio, S.J. 2001. Crop injury from sublethal rates of herbicide. I. Tomato. HortScience 36:669-673.
  • Gilreath, J.P., Chase, C.A. and Locascio, S.J. 2001. Crop injury from sublethal rates of herbicide. II. Cucumber. HortScience 36:674-676.
  • Gilreath, J.P., Chase, C.A. and Locascio, S.J. 2001. Crop injury from sublethal rates of herbicide. III. Pepper. HortScience 36:677-681.