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United States Department of Agriculture

Agricultural Research Service

Research Project: Alternatives to methyl bromide soil fumigation for vegetable and floriculture production

Location: Subtropical Plant Pathology Research

2009 Annual Report

1a. Objectives (from AD-416)
Identify impact of pest management tactics on functional diversity of soil microflora and weed populations, their competitive interactions, and effects on crop health. Conceive, develop, and test tactics for the control of plant diseases, parasitic nematodes and weed pests of vegetable and floriculture crops. Research efforts will concentrate on the testing of novel chemical, biological, biorational, cultural, and organic pest conrol tactics and on improving their application technology. Identify combinations of pest control tactics that interact synergistically to improve pest control, are practical to implement, and will minimize environmental disruption. Research activities will focus on identifying combinations of pest control tactics that produce synergistic effects and minimize disruption to conventional crop production practices. Define the impacts of pest management and crop production practices on soil health including the suppression of soilborne pests.

1b. Approach (from AD-416)
A rational and sustainable approach to finding viable alternatives to methyl bromide is to utilize integrated pest management (IPM) programs where combinations of tactics are used to maintain economic damage from key pests below a tolerable threshold. Another approach is to redesign production systems minimizing the potential for outbreaks of soilborne pests. Availability of biologically-based pest management tactics must be increased for successful IPM programs for soilborne pests to be implemented. Growers must have the option of choosing tactics that fit the needs and constraints of their individual programs. Deployment of multiple or companion tactics is essential to alleviate selection pressure and manage potential increases in resistant pest populations. Synergistic effects from combinations of pest management tactics need to be determined. Specific research methodology will include combinations of cultural practices, biotechnology, biological, and conventional control methods.

3. Progress Report
On-farm efficacy trials on alternative fumigants such as iodomethane:chloropicrin (50:50 Midas™) and dimethyl disulfide (Paladin™, 79:21) for control of weeds, root-knot nematodes (Meloidogyne spp.), and soilborne fungal and oomycete plant pathogens on floriculture crops including ornamental cockscomb (Celosia argentea var. cristata), snapdragon (Antirrhinum majus), and sunflower (Helianthus annuus) were completed. Results have provided growers with information on the spectrum of pests controlled by these approaches as well as with the use of soil solarization. Several interactions were identified between soil fumigants and cultivars selected that will assist growers in making planting decisions. Susceptibility of numerous weeds, cover crops, and floral crops to the major species of root-knot nematodes found in Florida was determined. Data on root-knot nematode/weed interactions were collected from several greenhouse studies and field trials assessing alternative fumigants combined with the use of grafted tomatoes and melons, and caladiums planted in fumigated and nonfumigated soil. One provisional patent application was filed on a novel combination of organic compounds that could decrease the dependence on existing broad-spectrum fumigants. In laboratory, greenhouse, and microplot trials very low concentrations of the active ingredient have resulted in a high level of efficacy with regard to weed, nematode, and oomycete pathogen control. Field trials were conducted to evaluate sunflower as a beneficial cover crop for vegetable growers currently relying upon soil fumigation for managing soilborne pests and as source of locally produced biodiesel. Field experiments were continued to determine the combined effects of novel fumigant application technology and soil preparation and a virtually impermeable film on the retention of 1,3-dichloropropene in the soil. Changes in soil microbial communities, populations of purple nutsedge populations and the soil density of root-knot nematodes were evaluated under continuous tomato monocultures or a sunn hemp cover crop and under various application rates of broiler litter and urban plant debris.

4. Accomplishments
1. New chemicals for weed, nematode, and pathogen control. Multiple laboratory, greenhouse, and microplot trials were conducted to evaluate a novel, reduced-risk compound for control of weeds, plant pathogenic fungi and bacteria, and plant parasitic nematodes. One compound was identified that has broad-spectrum pest control activity at very low application rates and poses no risk to the environment or the applicator, and a provisional patent has been filed.

2. Anaerobic soil disinfestation as an alternative to methyl bromide fumigation. A cooperative research project with the University of California, Santa Cruz has resulted in the generation of new information on a technique that utilizes the combination of composted broiler litter and a carbon source with soil saturation and heating to create an anaerobic condition that induces weed, nematode, and soilborne plant pathogen control. Greenhouse and field trials conducted by California cooperators allowed for the identification of an optimal approach for Florida trials in which multiple water levels were tested with molasses and broiler litter. When soil was amended with both litter and molasses, the effect on anaerobicity was stronger than that of either broiler litter or molasses alone. This approach was successful using a previously formed false bed. Control of yellow nutsedge emerging though the plastic early in the season in plots receiving the combination was equivalent to methyl bromide. At pepper harvest there were few significant differences between ASD treatments and the untreated check with regard to nutsedge emerging through the plastic. However, total weed biomass harvested from transplant holes at pepper harvest indicated that weeds in treatments including amendment with either molasses or broiler litter, regardless of applied irrigation, were controlled as well as with methyl bromide. Weed control with solarization alone was also better than the untreated check, though not equivalent to methyl bromide. Control of Phytophthora capsici, introduced in buried inoculum in nylon mesh bags, was equal to that of methyl bromide for all treatments except the untreated check. There was an indication of increased numbers of non-pathogenic, beneficial nematodes in some treatments. The weed control observed during the bell pepper trial was maintained during the eggplant double crop.

3. Short-Term Methyl Bromide Alternatives for the Florida Floriculture Industry. This cooperative research project with the University of Florida has yielded three seasons of new information on the use of soil solarization and fumigants including iodomethane and reduced rates and formulations of methyl bromide, applied under metalized films for weed, nematode and pathogen control in cut-flowers in Florida. Four seasons of data on snapdragon (Antirrhinum majus), and celosia (Celosia argentea) were collected from commercial production fields. Pest pressure varied according to location and ranged from high nematode and weed pressure, to low nematode but high weed pressure. Results of studies show that iodomethane applied under metalized film provided weed control comparable to high rates of methyl bromide (98:2 400 lb/a) under high density polyethylene film, and lower rates of methyl bromide (98:2 200 lb/a) under metalized film. Low rates of methyl bromide (67:33 mbr:chloropicrin 200 lb/a) under metalized film did not provide good weed control. Soil solarization provided better control of white clover (Trifolium repens) than any fumigant tested. Under high nematode pressure, iodomethane controlled root-knot nematodes in soil as well as methyl bromide, although populations rebounded late in the growing season with both fumigants. Early season nematode control; however, proved important.

4. Nutsedge management can be enhanced through the combination of mulching and the biological control agent, Dactylaria higginsii. Four seasons of field trials were conducted on one research farm and one commercial vegetable production farm using hay mulches combined with either Dactylaria higginsii or a Trichoderma sp. Field trials have confirmed that cogongrass infested with D. higginsii or Trichoderma sp., non-infested cogongrass and bahiagrass hays were most effective in suppressing nutsedge growth. The on-farm trials also included the treatment combination of a biodegradable paper mulch combined with plastic mulch. During the tomato cropping season, the combination of paper and plastic mulch resulted in the greatest reduction in the weed population. The approach of using the combination of paper and plastic mulch has been adopted by a number of commercial organic strawberry producers in California.

5. Management of Nematodes and other Soilborne Pests in Floriculture Production Systems. This Specific Cooperative Agreement with the University of Florida has yielded new information on susceptibility of a variety of important cut flower species to common species of root-knot nematodes in Florida. Experiments evaluating the susceptibility of selected flower cultivars to Meloidogyne incognita (race 2) and M. javanica revealed snapdragon and nasturtium were susceptible and supported high populations of both nematode species, while marigold, zinnia, salvia, and carnation cultivars evaluated were poor hosts. Delphinium showed light galling with some intermediate nematode population levels, but was significantly less susceptible than snapdragon and often similar to the resistant flower species. New data has also been generated on the use of soil solarization for nematode control in floriculture crops indicating that eggs and juveniles of Meloidogyne incognita can be killed over time at temperatures of 40-42oC, which are substantially lower than the temperatures of >45oC typically expected under solarization. However, lethal effects at reduced temperatures required exposure to those temperatures for >13 hours up to several days, so the recommendation to keep solarization films in place for 6 weeks remains unchanged.

6. Effects of management strategies on weed/nematode interactions. Three greenhouse and three field experiments were conducted to assess root-knot nematode/weed interactions. The replicated controlled greenhouse studies evaluated 19 plant species, including weeds and cover crops, to determine susceptibility to three major Meloidogyne species, and to determine relative nematode reproductive rates on each plant species. The three important root-knot nematode species evaluated were Meloidogyne incognita, M. javanica, and M. arenaria. Plant species differed in their susceptibility to each of the species of root-knot nematode, and in their susceptibility relative to each other. Data were also collected from three field trials evaluating alternative nematode and weed management strategies in vegetable and ornamental crops, including alternative fumigants such as methyl iodide, and DMDS, and integrated approaches employing organic amendments and soil solarization. In field trials, root-knot nematode galled weeds were identified and females were extracted from roots and identified. To date, the predominant species of root-knot nematode isolated from weeds in the field has been M. incognita.

7. Adaption of Vegetable Grafting Technologies to U.S. Fresh Vegetable Production. A cooperative research project with the University of Arizona has generated four growing seasons of data on the use of grafting for root-knot nematode control in tomato, muskmelon, and watermelon. A series of field experiments was completed in a field infested with root-knot nematodes (Meloidogyne spp.) that affect vegetable and ornamental crops in Florida. A split plot experimental design with four replications was used to evaluate rootstock/scion combinations in untreated and fumigated soil treated with methyl bromide, iodomethane, or dimethyl disulfide. Sub-plots in the primary tomato crop consisted of three rootstocks with some reported resistance to nematodes, and the non-grafted hybrid cultivar FL-47, which was also used as the scion for the grafted seedlings. Treatments were evaluated throughout the season for plant growth and disease, and at the end of the season for nematode resistance, yield, and fruit quality. A double crop of muskmelon was planted in the existing beds following completion of the tomato trial in year 1, and watermelon was used in year 2. In year 1, two muskmelon rootstocks were evaluated with the non-grafted scion ‘Athena’ on its own rootstock. In year 2, two watermelon rootstocks were evaluated with the non-grafted scion ‘TRI-X Brand Palomar’on its own rootstock. Melons were evaluated throughout the season, and at the end of the season as described for tomatoes. Two years of additional microplot experiments were conducted concurrently with tomato and melon field trials using the same grafted tomato and melon transplants and were inoculated with nematodes to insure data availability on the host status on rootstocks for Meloidogyne incognita. Results show that galling and soil populations of root-knot nematodes on tomato, muskmelon, and watermelon can be reduced with resistant rootstocks.

Review Publications
Burelle, N.K., Bausher, M.G., Rosskopf, E.N. 2009. Greenhouse evaluation of capsicum rootstocks for management of meloidogyne incognita on grafted bell pepper. Nematropica 39:121-132.

Chellemi, D.O. 2009. Incorporating pest management into the design of multiple goal-oriented cropping systems. Phytoparasitica 37:101-103.

Kubota, C., Mcclure, M., Burelle, N.K., Bausher, M.G., Rosskopf, E.N. 2008. Vegetable Grafting: History, Use, and Current Technology Status in North America.. HortScience. 43(6):1664-1669

McSorley, R., Wang, K.-H., Rosskopf, E.N., Kokalis-Burelle, N., Petersen, H.N.H., Gill, H.K., Krueger, R. 2009. Nonfumigant alternatives to methyl bromide for management of nematodes, soil-borne disease, and weeds in production of snapdragon (Antirrhinum majus). International Journal of Pest Management 55 (4), pp. 265-273

Last Modified: 07/25/2017
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