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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

2013 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:
This is the final report for the project 5302-13220-004-00D, which was terminated on December 25, 2012 and merged with project 5302-13000-011-00D. Details of progress on milestones relating to methyl bromide alternatives research can be found in the 2013 Annual Report for 5302-13000-011-00D. Substantial results were obtained over the 5 years of the project. Dose response of low toxicity chemicals including acrolein and dimethyl disulfide as replacements for pre-plant methyl bromide fumigation was developed in cut flower production to control weeds and pathogens. Use of these soft chemicals has potential impact on weed and disease control in areas where township caps and buffer zone requirements preclude the use of the other alternatives such as 1,3-D. Etiology of calla lily root pathogenic isolates was molecularly characterized by PCR amplification and restriction enzyme digestion, which provided understanding of genetic composition of soil pathogens in ornamental crops. Biofumigation with soil-incorporated plant materials demonstrated measurable production of volatile methyl sulfide and dimethyl disulfide gases and the beneficial impact on controlling soilborne pathogens. Chemical combinations of 1,3-D plus chloropicrin, iodomethane plus chloropicrin, and propargyl bromide generally controlled root-knot and citrus nematodes similar to methyl bromide in grape replant soil fumigation treatment. Replanting of perennial orchards and tree and vine nurseries in California depends on soil fumigation for production and delivery of nursery crops free of economically important plant parasitic nematodes. A series of field trials showed that effective nematode control was achievable with half rates of 1,3-D when the field was covered with low impermeable plastic films. Use of these low permeability films also drastically reduced both peak flux and cumulative fumigant gas emissions, which is beneficial to protect worker exposure risk and regional air quality. In addition to films, field studies also tested and showed that fumigant emissions were significantly reduced using water seal or chemical and organic amendments. Field trials also demonstrated that spot fumigation achieved a 10-fold reduction in atmospheric volatile organic compounds load in orchard replant soil fumigation. Field trials on herbicide efficacy and crop safety contributed to the overall effort on methyl bromide alternatives for weed control in field perennial woody nurseries. The overall impact of the accomplishments is that ornamental and cut flower, perennial nursery, grape, and orchard growers have new information on which to make decisions concerning soil fumigation with methyl bromide alternatives to maximize profits while sustaining yield.

4. Accomplishments
1. Extraction and amplification of pathogen DNA from soil. Soil pathogen assays are usually carried out in the laboratory using traditional plating techniques for commonly found species such as Verticillium dahliae, Fusarium oxysporum, Pythium spp. and Phytophthora cactorum. This kind of analysis tends to be site specific, therefore, a study was initiated on extraction and amplification of pathogen DNAs. Soil samples were collected in fumigated strawberry fields and flower fields. DNA of the calla lily pathogen was extracted from soil samples collected from diseased fields and has been successfully amplified using PCR. The methodology developed for successful extraction and amplification of pathogenic DNAs from soil can lead to a quantitative assay for the pathogens and enable much improved management of soilborne diseases in ornamental and strawberry production in California or anywhere in the world.

2. Fumigant behavior in soil and nematode control. The efficacy of nematode control in soils with deep rooted tree crops requires fumigant movement to deeper depths. Limited research is available for this effect, therefore, a field trial was conducted to evaluate fumigant behavior and nematode control in an almond orchard near Merced, California. Fumigation treatments included three surface sealing methods (bare soil, standard polyethylene film or PE film, and a totally impermeable film or TIF film) and four application rates of Telone C35. The TIF film significantly reduced fumigant emission peak flux compared to the standard PE film. All full rate treatments achieved 100% kill of the residential nematodes in the top 3 foot soil, but we found survival nematodes in the 3 to 5 foot soil depth. The findings provide valuable information to growers, the soil fumigation industry, and regulatory agencies regarding the use of TIF film with respect to fumigant movement in soil and nematode control, and further highlight existing difficulties in controlling nematodes at deep soil depths.

Review Publications
Gao, S., Ajwa, H., Qin, R., Stanghellini, M., Sullivan, D. 2013. Emission and transport of 1,3-dichloropropene and chloropicrin in a large field tarped with VaporSafeTM TIF. Environmental Science and Technology. 47:406-411.

Last Modified: 06/27/2017
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