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.
The agreement was established in support of the Objective 3 of the in-house project, and the goal was to develop effective and practical methyl bromide alternatives with minimal air and water quality concerns in soil fumigation. New environmental regulations to protect air and water quality in California require soil fumigation with methyl bromide alternatives to have minimum impact on the environment. Crops with specific fumigation needs include perennial nurseries that require 100% nematode control and grapes and strawberries that require soil fumigation before planting a new crop. In 2009, analyses of data from existing methyl bromide alternatives projects for grapes were carried out. The root-knot and citrus nematodes, which are often present in the replant problems of grapes in the San Joaquin Valley, California, were evaluated following an 8-year methyl bromide alternatives fumigation trial. The study revealed that 1, 3-dichloropropene plus chloropicrin, iodomethane plus chloropicrin and propargyl bromide were as effective as methyl bromide against both root-knot and citrus nematodes. Rootstock Freedom was highly resistant to root-knot nematodes and not to citrus nematodes. Rootstock 1103P was partially tolerant to root-knot and citrus nematodes, but the tolerance broke down after 3 and 4 years, respectively. Pre-plant fumigation with propargyl bromide and replanting with 1103P rootstock was the only combination that gave similar yield as methyl bromide during the first four years of fruit production. Also in 2009, laboratory tests were carried out to test different dosages of dimethyl disulfide (DMDS) under different soil moisture and exposure time for killing citrus nematodes. Initial results showed that after 3 and 6 h of exposure, citrus nematodes were mainly active in the lowest dosages and inactive at the highest dose tested where less than 20% nematode mortality was obtained. After 24 h of exposure nematode mortality was substantial in the 64, 128 and 256 mg/L treatments. After 96 h, nematode mortality in the highest dose was above 60% and no active nematodes were found, whereas 32 and 64 mg/L rates had only active and inactive nematodes. The DMDS efficacy against citrus nematodes increased as the dose and time of exposure increased. The soil water content affected the efficacy of DMDS. At low rates this fumigant had generally better citrus nematode control in low soil moisture contents (10 and 30% moisture). At high dosage tested (256 mg/L soil air space) soil moisture content did not affect the efficacy of DMDS. Two new projects were also initiated in 2009: one on the efficacy of DMDS in field grapes and one on fabrics for preventing nematode and pathogen diseases in strawberry roots. Findings from this collaborative research will benefit US growers who historically relied on soil fumigation with methyl bromide and the average citizens in general by protecting the air and water quality. The project is monitored by the ADODR through regular email and telephone communications with the cooperator.