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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

2009 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
Dose response studies with acrolein in the lab have been completed. Laboratory experiments are currently being conducted to test efficacy of dimethyl disulfide (DMDS) for controlling various soilborne plant pathogens. Pathogen control evaluations were made on cooperating methyl bromide alternatives field trials led by unit members. Ornamental crop field trials on methyl bromide alternatives in Nipomo, Moss Landing, Oxnard, and Carlsbad, CA were completed. Field fumigation trials documenting nematode control with methyl bromide alternatives were completed and four new fumigation trials were established at the USDA research station or at cooperating nurseries. In open-field perennial crop nurseries, shank-injected, fumigants with plastic tarps generally provided better nematode control than drip-applied materials or untarped applications. Iodomethane:chloropicrin treatments generally provided nematode control as good as 1,3-dichloropropene but not as good as methyl bromide. Soil column studies were carried out to investigate the relationship between soil water content and fumigant emissions in three different textured soils (sand, sandy loam and loam). Data for a loam soil were complete and experiments for comparing with other two textured soils are on-going. Results indicate that increasing soil water content up to field capacity can result in linear reduction in emission flux in a loam soil. Reduction of emission flux was more profound than reduction of cumulative emission loss. Reduction of emission flux is significant to improve the buffer zone requirement during fumigation while reducing total emissions helps address volatile organic compound (VOC) issues in improving air quality in California. Four field trials were conducted to evaluate fumigant emission reductions using subsurface drip, spot-drip, strip-shank, modified shank vs. broadcast shank applications, low permeable tarps, and surface soil water or amendment treatments. Post-water treatments with sprinklers can effectively reduce peak emission flux than cumulative emission loss. Surface soil amendment with composted manure alone without water treatments can not always result in reduced emissions. Virtually impermeable films (VIF) can reduce emission flux and cumulative emission loss significantly as well as improve pest control. Further research is planned for testing more flexible low permeable tarps. This research continues to provide solutions to effective use of soil fumigants and minimize their negative environmental impacts. Ten new screening trials were initiated in cooperation with perennial crop nursery operations including producers of walnut, almond, stonefruit, and garden rose planting stock. Pre-emergence applications of pendimethalin, oryzalin, and dithiopyr were generally safe to nursery stock and controlled many weed species. Rimsulfuron, flumioxazin, oxyfluorfen, sulfentrazone, imazosulfuron provided even better weed control at the expense of variable crop safety. Relatively new or reformulated products including: indaziflam, penoxsulam, sulfosulfuron, halosulfuron, prodiamine, oxyfluorfen, etc., have been evaluated in small-scale nursery tests.

4. Accomplishments
1. Tree Site Specific Spot Fumigation Can Reduce Total Fumigant Emissions. Reducing emissions of volatile organic compounds (VOCs) from fumigant pesticides is mandatory in California, especially in “nonattainment areas” like the San Joaquin Valley that do not meet federal air quality standards. A two-year field study was conducted by ARS scientists in Parlier, CA to examine the feasibility of site-specific fumigant application only at future tree sites which dramatically reduced amounts of fumigant on an orchard basis. Cumulative atmospheric emission of the fumigants was estimated to be 18 to 23% of the applied active ingredients in plots that had been cover cropped with Sudan grass and 2 to 6% in plots that had remained bare for several months before treatment. Considering the significantly small amount of fumigant used on an orchard basis, the spot fumigation may achieve a 10-fold reduction in atmospheric volatile organic compounds (VOCs) load from fumigant pesticides.

2. Low Permeable Film Can Effectively Reduce Emissions From Soil Fumigation Under Various Field Applications. The potential of using virtually impermeable film (VIF) to reduce emission from field soil fumigation has been questioned because of potential damage to the film during field installation. Field trials were conducted by ARS scientists at Parlier, CA and emission data collected which indicate that the VIF can reduce emissions down to 1-3% of totally applied fumigant compared to emissions >60% without the VIF. Furthermore, the VIF film can retain higher fumigant concentrations under the tarp than the commonly used polyethylene film that helps improve pest control. Thus, VIF tarp is an effective means to reduce fumigant emissions and improve efficacy as long as the film is successfully installed in the field. The information is valuable for growers, policy makers and researchers for identifying effective agricultural practices towards emission reduction from soil fumigation.

3. Organic Amendment Alone Applied to Surface Soil Without Water Treatment Does Not Aways Result in Reduced Fumigant Emissions From Soil Fumigation. Incorporation of organic materials to surface soil could be an effective strategy to reduce fumigant emissions. However, the potential to reduce emissions in the field has not been adequately evaluated. Data from field trials conducted by ARS scientists in Parlier, CA indicate that incorporation of composted manure at 5, 10 and 20 tons per acre did not significantly reduce emissions from soil fumigation. This research concludes that surface soil amendment with various rates of composted manure did not always result in emission reductions from field fumigation although some laboratory results showed organic materials can effectively degrade soil fumigants and reduce emissions. The information is useful for growers, policy makers and researchers in identifying effective agricultural practices that reduce emissions from soil fumigation.

Review Publications
McDonald, J.A. S. Gao, R. Qin, B.D. Hanson, T.J. Trout, and D. Wang. 2009. Effect of water seal on reducing 1,3-dichloropropene emissions from different soil textures. Journal of Environmental Quality. 38: 712-718.

Hanson, B.D., A. Shrestha, D.L. Shaner. 2009. Distribution of Glyphosate-Resistant Horseweed (Conyza Canafensis) and Relationship to Cropping Systems in the Central Valley of California. Weed Science. 57:48-53

Qin, R., S. Gao, D. Wang, B.D. Hanson, T.J. Trout, and H. Ajwa. 2009. Relative effect of soil moisture on emissions and distribution of 1,3-dichloropropene and chloropicrin in soil columns. Atmospheric Environment. 43:2449–2455.

Guo, M., and S. Gao. 2009. Degradation of methyl iodide in soil: effects of environmental factors. J. Environ. Qual. 38:513-519.

Schneider, S.M., B.D. Hanson, J.S. Gerik, A. Shrestha, T.J. Trout, S. Gao. Comparison of Shank-and-Drip-Applied Methyl Bromide Alternatives in Perennial Crop Field Nurseries. 2009. HortTechnology. 19:331-339.

Last Modified: 07/22/2017
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