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United States Department of Agriculture

Agricultural Research Service

Research Project: Reducing Air and Water Quality Issues with Methyl Bromide Alternatives in California
2013 Annual Report


1a.Objectives (from AD-416):
To develop, test, and demonstrate effective and practical field management techniques for nematode pest control with minimal air and water quality concerns in soil fumigation with methyl bromide alternatives.


1b.Approach (from AD-416):
Surface barriers such as extremely low permeability plastic films will be used under field conditions to enhance pest nematode control and reduce fumigant emissions to the air. Soil amendments with natural organic materials such as animal manure or synthetic chemicals will be evaluated alone or in combination with the low permeability films to enhance fumigant decomposition thus reducing emission potential and protect air quality. Application of fumigants with irrigation systems will be tested in comparison with shank injection methods and potential for deep percolation and surface runoff will be evaluated. Impact of soil organic and inorganic amendments on air and water quality will also be measured. Documents SCA with UC Riverside.


3.Progress Report:

This research contributes to Objective 5 of the in-house parent project. Soil fumigation is often used for killing soilborne plant pathogens and nematodes, especially in high value crops such as nursery production of fruit and nut tree seedlings as well as in orchard and vineyard replanting situations. The use of any fumigants is highly regulated for human health and safety concerns and for protecting air and water quality. A new nematology postdoc was hired, who carried out field trials in the central valley of California to quantify pest control efficacy of methyl bromide alternative chemicals. In cooperating with other project members, air emissions of methyl bromide alternative chemicals were measured. Techniques for reducing emissions included water seal and low permeability films. Soil moisture was also monitored to determine if any potential leaching of fumigant chemicals would occur to pose any water quality concerns. This is needed for the water seal approach. Another field investigation was carried out to evaluate the performance of reduced rates of a mixture of 1,3-dichloropropene and chloropicrin under a polyethylene or a low impermeable film against soil-borne plant-parasitic nematodes and pathogens. The fumigants applied at full rate, three fourths, half, and one fourth of full rate, were all highly effective in controlling nematodes under both plastic films. The reduced rates performed well against Pythium spp. and Verticillium spp. but lacked control for Fusarium spp., and Phytophtora spp. Soil gas evaluations demonstrated that the low permeable film increased the chemical concentrations in soil compared to polyethylene film. Findings from these field trials were summarized in manuscripts published in California Agriculture. Data analyses of a long-term methyl bromide alternatives projects for grapes were carried out. The dataset consisted of 8-year nematode and grape yield response data as a result of a number of fumigation treatments plus non-fumigated controls and non-fumigated rootstock treatments. This research resulted in two peer-reviewed manuscripts published within the project period. Plant-parasitic nematodes and soilborne pathogens can reduce the overall productivity in grape production. A new field project was also initiated on the efficacy of post-plant application of dimethyl disulfide in field grapes. The focus was on the efficacy of drip-applied dimethyl disulfide, as a therapeutic treatment, against nematodes and pathogens in existing vineyards and crop responses to the chemical application. Two microplot and two field trials were conducted to investigate the effect of dimethyl disulfide applied as a post-planting treatment against soilborne plant-parasitic nematodes, pathogens, and on yield in established grape vines. In microplot and field trials, post-plant fumigation with dimethyl disulfide controlled citrus (Tylenchulus semipenetrans), root-knot (Meloidogyne spp.), pin (Paratylenchus spp.), and ring (Mesocriconema xenoplax) nematodes in established Thomson Seedless grape vines. However, dimethyl disulfide did not control the soilborne pathogens Pythium ultimum and Fusarium oxysporum. No indications of phytotoxicity were detected after post-plant fumigation with dimethyl disulfide. In the field trial grape yield was significantly higher in the lowest dimethyl disulfide rate but there was no difference in other rates, compared to the untreated control. Post-plant fumigation with dimethyl disulfide controlled plant parasitic nematodes in established grape vines but had less action against soilborne pathogens. Low rates of dimethyl disulfide were sufficient for nematode control, increased the yield, and probably without affecting beneficial soil organisms. A manuscript on the dimethyl disulfide work was submitted to a peer-reviewed journal for publication. Research findings throughout the project period were also presented at national and international conferences, and local stakeholder meetings. The overall impact of the accomplishments is that California growers of specialty crops such as grapes and tree crops have new information on which to make soil fumigation decisions with reduced air and water quality concerns.


Last Modified: 11/27/2014
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