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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

2010 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. Formerly 5302-13220-003-00D (12/07).

3. Progress Report
Laboratory dose response studies with acrolein and dimethyl disulfide were completed for control of various soilborne pathogens and weeds. Pathogen control evaluations were made on cooperating methyl bromide alternatives field trials. Ornamental crop field trials using steam as a methyl bromide alternative were initiated in Nipomo, Carlsbad, and Oxnard, CA. An ornamental crop field trial on methyl bromide alternatives using dimethyl disulfide was initiated in Oxnard, CA. Data analysis and report writing were carried out on two multi-year fumigation projects in vineyards and nematode control assessments using various methyl bromide alternative treatments. A manuscript was completed and will be submitted in 2010. Crop response and nematode control efficacy were also measured from three ongoing grape replant field trials. A new study was initiated to test dimethyl disulfide for controlling nematodes in grapes. A greenhouse and a companion field study was initiated to determine nematode control in strawberries using substrate media and landscape fabrics. Emission reduction studies from soil fumigation were conducted through laboratory experiments and field trials. A soil column study was completed to investigate the relationship between soil water content and fumigant emissions in three different textured soils (sand, sandy loam and loam). Data for all three soils were compiled and a manuscript is in preparation. The data show how increasing soil water content up to field capacity affects 1,3-dichloropropene and chloropicrin emissions (flux and cumulative emission loss). A laboratory batch experiment was also initiated to determine fumigant persistence in soils from different application rates. Three field trials were conducted to evaluate the potential of a new low permeable tarp (totally impermeable film or TIF) to reduce emissions, improve fumigant distribution in soil profile, and/or reduce application rates. A report was prepared and a manuscript is being developed. Two field trials using small field plots were conducted in the San Joaquin Valley to determine the potential of TIF tarp to reduce emissions, improve fumigant distribution in soil and reduce fumigant application rate for perennial orchards and nurseries. Sample analyses or data compiling are on-going for these two trials. Ten herbicide trials in tree and rose nurseries established in 2009 were completed. Weed control and crop safety evaluations of pendimethalin, oryzalin, and dithiopyr which were generally safe to nursery stock and controlled many weed species. Relatively new or reformulated products including: indaziflam, penoxsulam, sulfosulfuron, halosulfuron, prodiamine, oxyfluorfen, also were evaluated in small-scale nursery tests.

4. Accomplishments
1. Methyl bromide alternatives for Gladiolus production. Methyl bromide soil fumigation has traditionally been used for Gladiolus production in California. Field trials were conducted by ARS scientists in Parlier, CA to test methyl bromide alternative chemicals in Gladiolus production. All chemical treatments reduced the pathogen populations in both the drip and the shank trials compared to the untreated controls except for Telone C35 which did not perform well for control of Fusarium oxysporum in the shank trial. Bulb yield from the alternative treatments was generally comparable to the standard methyl bromide/chloropicrin treatment. Overall, pathogen and yield seemed to be slightly better in the shank treatments compared to the drip treatments. From these results, it appears that a successful Gladiolus bulb crop can be grown with these alternative treatments.

2. Controlling soil pathogens with steam. Steam is a possible non-chemical methyl bromide alternative for killing soilborne pathogens; however, there are no field data to support this potential benefit. Field trials were carried out by ARS scientists in Parlier, California to apply steam via drain tile or spike hose to control soilborne plant pathogens. Compared to untreated control soil, populations of Fusarium oxysporum and Pythium species were not significantly different in soils immediately after steam treatment with the spike hose. Fusarium populations at 4 months after steam treatment with the drain pipe were significantly lower in one of four trials than the untreated control. This research indicated a mixed success with steam to control these soil pathogens.

3. Effect of dimethyl disulfide on soil pathogens and nematodes. Dimethyl disulfide (DMDS) is a potential methyl bromide alternative for pre-plant soil fumigation; however limited data are available on its efficacy against soil fungal pathogens, weeds, and nematodes. Laboratory experiments were conducted by ARS scientists in Parlier, California to determine the critical dose of DMDS needed to provided adequate pest control. Nematode control was very good at reasonable rates and exposure times. Poor fungi and weed control was observed at all DMDS concentrations. This research indicates that DMDS can be a potential methyl bromide alternative for nematode control but not for fungi and weeds.

4. Methyl bromide alternatives for grape replant. Methyl bromide soil fumigation is often required during replantation of a new vineyard. In an eight-year grape replant trial, ARS scientists in Parlier, CA found that 1,3-dichloropropene plus chloropicrin, iodomethane plus chloropicrin, and propargyl bromide generally controlled root-knot and citrus nematodes similar to methyl bromide. However, only propargyl bromide treatments had grape yield equivalent to methyl bromide during the first four years after treatment. Rootstock selection had a profound effect on nematode populations; the root-knot resistant rootstock ‘Freedom’ kept nematode numbers low regardless of preplant fumigation treatment. Where this particular race of root-knot nematode is the major replant problem, use of a resistant rootstock may reduce the need for preplant fumigation; however other replant problems such as different nematodes or soil-borne pathogens may still exist.

5. Fumigant emissions affected by soil type and water content. Soil fumigation is practiced across different soil types and soil moisture conditions; however, the effects of differences in soil texture and water content on atmospheric emissions are not well understood. The relationship between soil type, water content, and fumigant emissions was examined by ARS scientists in Parlier, California. Increasing water content up to field capacity reduced peak emission rate, delayed emission occurrence time, and reduced total emissions. This effect appeared to be more significant in fine-textured than in coarse-textured soils. This finding is useful for growers and fumigation practitioners to develop effective agricultural practices towards reducing fumigant emissions.

6. Low permeable films reduce fumigant emissions. A new low permeable film, referred to as totally impermeable film or TIF, effectively reduced fumigant emissions in laboratory tests; however, no field data are available. One large field trial was conducted by ARS scientists in Parlier, California to test the new film for reducing fumigant emissions under field conditions. The TIF reduced peak emission rate up to 10 times lower than that from the standard polyethylene (PE) film. Over a 6-day field covering period, the total emission loss was reduced to below 2% of total fumigant applied compared to 30% emission with the PE film. However, the emission surge upon cutting the TIF tarp was much higher than with the PE film indicating that a longer waiting time would be needed to reduce potential exposure risks. The research showed that using this new film will help improve buffer zone restrictions and enable many fields to be fumigated under the newly amended United States EPA regulations.

7. Herbicide crop safety in perennial woody nurseries. Weed control is an important concern for production of woody nursery crops in California, however, phytotoxicity information is often not available for existing and new herbicides. ARS scientists in Parlier, California conducted 2-year field trials to determine the most promising herbicides. The herbicides pendimethalin, thiazopyr, and dithiopyr can be safely used in the nurseries. The herbicide oxyfluorfen was differentially phtotoxic to some nut tree rootstocks in the nursery. A series of sulfonylurea herbicides were phytotoxic in tree nurseries. The herbicide foramsulfuron was not phytotoxic to a peach rootstock. The results of these herbicide evaluations contribute to the selection and adoption of new weed control strategies in perennial nurseries.

Review Publications
Wang, D., C. Rosen, L. Kinkel, A. Cao, N. Tharayil, J. Gerik. 2009. Production of methyl sulfide and dimethyl disulfide from soil-incorporated plant materials and implications for controlling soil-borne pathogens. Plant Soil. 324:185-197.

Suduan Gao, Ruijun Qin, Bradley D. Hanson, Nishanth Tharayil, Thomas J. Trout, Dong Wang and James Gerik Effects of Manure and Water Applications on 1,3-Dichloropropene and Chloropicrin Emissions in a Field Trial. J. Agric. Food Chem., 2009, 57 (12), pp 5428–5434.

Wang, D., G. Browne, S. Gao, B. Hanson, J. Gerik, R. Qin, N. Tharayil. 2009. Spot fumigation: fumigant gas dispersion and emission characteristics. Environ. Sci. Technol. 43:5783-5789.

Last Modified: 05/28/2017
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