2012 Annual Report
Alternatives for soil fumigation with methyl bromide for grape replant were evaluated as a continuing project of the Areawide Methyl Bromide Alternatives Program. In the wine grape (Vitis vinifera var. Cabernet Sauvignon) plot experiments, soil nematodes and yield were measured. The data indicates a positive fumigation effect on yield and reduction in nematodes. Relatively low yields were found in the non-fumigated field plots and the low rate bare soil plots. In the raisin grape (Vitis vinifera var. Selma Pete) grower field trial, results showed lower yield values in the untreated control than in all fumigated crop rows. The two Telone C35 treatments showed similar yield to the methyl bromide control.
Two field trials and laboratory experiments were conducted from June 2011 through June 2012 on emission reduction and efficacy improvement in soil fumigation. One trial was conducted in an annual crop field. Data on emission and soil fumigant were collected from the field tarped with totally impermeable film (TIF) and in tarp-edge areas. Results were reported at meetings and submitted to regulatory agency to assist in modeling efforts for regulation development. Another trial was conducted in a perennial field. Emission reduction by TIF and the effect of using reduced rates and carbonation (adding carbon dioxide to fumigant and using it as a dispersant in application) under TIF on fumigant distribution in soil and efficacy on nematodes, pathogens and weeds were investigated. A laboratory study was conducted on the degradation of several important fumigants affected by application rates. Research data were presented at growers and scientific meetings with three manuscripts in preparation. Results on emission reduction and efficacy improvement from soil fumigation were summarized and posted on the website of Pacific-Area Wide Program for Methyl Bromide Alternatives (http://ucanr.org/sites/PAWMBA/Emissions_Projects/Emission_Reduction/). This research continues to determine field effective fumigation rates under TIF.
2. Fumigant degradation varies with application rate. Low permeability tarps effectively retain soil fumigant under tarp to reduce emissions while increasing concentrations in soil. This leads to the potential of using reduced fumigant rates to control soil pests. However, there is a significant knowledge gap on the relationship between fumigant concentration in soil and rates of degradation. A laboratory study was conducted to determine degradation rates of several important methyl bromide alternatives including 1,3-dichloropropene, chloropicrin, and dimethyl disulfide in five soils. Data show degradation of these fumigants is highly dependent on both the chemical and application rate. Fumigant degradation rates decrease significantly with increased application rates for chloropicrin and dimethyl disulfide, but much smaller changes are observed for 1,3-dicnloropropene compounds. The findings indicate fumigant degradation rates affect effective fumigant application rates under low permeability tarps. 3. TIP tarp and carbonation to reduce fumigation rate. The benefits of using reduced rates for satisfactory pest control with TIF tarp was evaluated in soil fumigation for perennials that require deep injection and effective dispersion of fumigants to control pests throughout soil profile. TIF tarp and carbonation techniques were tested in a field trial on fumigant emission, fate, and distribution in soil as well as efficacy to determine the potential of using reduced chemical input. TIF was proven to reduce emissions >95% relative to bare soil while standard PE tarp reduced emissions ~30%. TIF significantly increased fumigant concentration or concentration-time exposure indices at 15 cm depth relative to the PE film. Reduced 2/3 fumigant rate under TIF showed the possibility to provide effective nematode control in soil profile, but the improvement on fumigant distribution by carbonation is inconclusive and relies on more field tests. This research continues to provide information on effective use of soil fumigants while minimizing environmental impact for many perennial crops. 4. Etiology of calla lily root pathogen. Thirty-nine isolates of Pythium sp. were recovered from diseased roots of calla lily taken from multiple locations in production fields and tested for pathogenicity in a greenhouse test. All the pathogenic isolates were characterized using PCR amplification and restriction digestion of the Cyclooxygenase-1 & 2 genes. Thirty-five of the isolates were pathogenic and expressed the same genotype; the non-pathogenic isolates exhibited different genotypes. These data suggest the Pythium isolates from these multiple locations are identical; identification of this isolate down to species is in progress. This work will facilitate rapid identification and quantification of a serious calla lily pathogen which impacts grower decisions of soil fumigation.
Jhada, A., Gao, S., Gerik, J.S., Qin, R., Hanson, B. 2012. Effects of surface seals and application shanks on nematode, pathogen and weed control with 1,3-dichloropropene. Pest Management Science. 68(2):225-230.
Wang, D., Yates, S.R., Gao, S. 2011. Chloropicrin emissions after shank injection: Two-dimensional analytical and numerical model simulations of different source methods and field measurements. Journal of Environmental Quality. 40:1443-1449.
Cabrera, A., Wang, D., Schneider, S.M., Hanson, B. 2012. Subsurface drip application of methyl bromide alternative fumigants for controlling nematodes in replanted grapevines. Pest Management Science. 68:773-780.