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United States Department of Agriculture

Agricultural Research Service

Research Project: Alternatives to MEBR for California Cropping Systems

Location: Water Management Research

2012 Annual Report

1a. Objectives (from AD-416):
Test emerging methyl bromide alternative chemicals for their efficacy in controlling various soilborne plant pathogens in cut flowers and other ornamental crops. Test methyl bromide alternative chemicals, rates, and application methods to meet California certification standards for nematode-free production of tree, vine, and rose nurseries. Develop various application methods, soil amendments, and physical barriers to reduce the emissions and enhance efficacy of the chemical alternatives to methyl bromide. Develop integrated weed control strategies using combinations of methyl bromide alternative fumigants with herbicides and non-chemical management techniques to improve weed control.

1b. Approach (from AD-416):
Research techniques will include extraction of soil fungal pathogens and nematodes, isolation and identification, population assessment and identification of native weeds, in-situ measurements of fumigant emissions and fumigant gas dispersion in soils, and determining impacts of various combinations of fumigant formulation and surface containment on efficacy and emission reductions. Experimental platforms will range from laboratory microcosms, soil columns, greenhouse pots, to small field plots and demonstration-scale field trials. Stakeholder participation in planning and implementation of research trials will be crucial. Outcomes from these research activities will be transferred to the stakeholders.

3. Progress Report:
Pathogen control evaluations were made on cooperating methyl bromide alternatives field trials. Ornamental crop field trial on methyl bromide alternatives using chloropicrin and 1, 3-dichloropropene and non-permeable tarps is ongoing in Moss Landing, CA. This experiment will conclude in December 2012. Soil pathogen assays for the fall Parlier fumigation experiment have been completed. Assays were conducted for Verticillium dahliae, Fusarium oxysporum, Pythium spp. and Phytophthora cactorum. A study was initiated on fumigation effect on microbial community structure using phospholipid fatty acid analysis. A study of the etiology of the root rot disease of calla lily in the Moss Landing area was completed. Pythium spp. isolates were collected from diseased calla lily roots from production fields. The isolates were tested for pathogenicity in a greenhouse assay and confirmed to be the causative agent. Pathogenic isolates were evaluated using PCR and restriction enzyme digestion profiles were used to determine identity. 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 ( This research continues to determine field effective fumigation rates under TIF.

4. Accomplishments
1. Emission reduction by TIF and tarp-cutting time determined in large field trial. Tarping fumigated fields with low permeability films such as commercial product TIF (totally impermeable film) can significantly reduce emissions, but can also increase fumigant residence time in soil and would require extended tarp-covering durations to reduce potential exposure of workers and bystanders to fumigants. In collaboration with university researchers and industry as well as regulatory agency, a large field study was conducted in 2011 and determined the effect of TIF on emission reduction and tarp-cutting time. Comprehensive data on emission reduction and fate and transport of fumigants in soil were collected in an 8-acre field fumigated with a mixture of chloropicrin and 1,3-dichloropropene (Pic-Clor 60). Low emission flux was measured throughout tarp-covering of 16 days with total emission loss <10%, and < 1% at the tarp edges. Emission flux upon tarp-cutting increased, but was substantially lower than 5 or 6 days of tarp covering. This study demonstrated the ability of TIF to significantly reduce fumigant peak flux and total emissions and required longer tarp-cutting time for using 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.

Review Publications
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.

Last Modified: 06/23/2017
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