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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

2008 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 experiments were conducted to determine critical dose of acrolein to control several soilborne plant pathogens. Dose response of Agrobacterium tumefaciens to several other chemicals was also determined. One field trial on methyl bromide alternatives for cut-flowers has been completed in Carlsbad, CA, and four others are underway in Soledad, Nipomo, Santa Maria, and Oxnard, CA. New laboratory trials to determine critical dose of dimethyl disulfide (DMDS) for controlling various soilborne plant pathogens are underway. A series of field trials were completed on testing low rate MeBr applications under low permeability tarp in perennial crop nursery systems. In a single crop cycle, low rates of MeBr and 1,3-dichloropropene (1,3-D) under low permeability film were as effective as standard MeBr treatments for controlling plant parasitic nematodes while weed control tended to decrease with alternatives. Several fumigation experiments were initiated at the USDA facility and in cooperating nursery fields to test the impact of surface seal treatments (water seals, plastic films) on the nematode and weed control efficacy with 1,3-D and chloropicrin (CP). Although data analysis is ongoing, preliminary results suggest a strong effect of surface seal treatment on enhancing weed and nematode control in the upper soil layers. A large field trial was conducted in Oxnard, CA for testing the efficiency of two low permeable plastic tarps, virtually impermeable film (VIF) and semi-impermeable film (SIF) on reducing fumigant emissions in strawberry production. A standard polyethylene (PE) film with or without water applications in furrows was included for comparison. Emissions of 1,3-D and CP from top of the beds and furrows were measured using dynamic flux chambers. Total emission loss from the VIF and the SIF tarped fields was approximately 60% of that from the PE field. The preliminary results demonstrated that low permeable films were effective in reducing emissions. Water seal in furrows in the PE tarped field did not reduce total emissions, compared to the no water seal treatment, due to the low emission flux from the furrows. Additional data analysis is ongoing. Thirteen herbicide screening trials were initiated in cooperation with four perennial crop nursery operations (walnut, almond, stonefruit, and garden rose production) throughout the Central Valley of California. All treatments were applied to fumigated fields. Pre-emergence applications of pendimethalin, oryzalin, and dithiopyr were generally safe to nursery stock and controlled many weed species. Several other herbicides such as rimsulfuron, flumioxazin, sulfentrazone, imazosulfuron provided even better weed control at the expense of variable crop safety. Further research on the interaction between fumigation and herbicide treatments as well as herbicide application rate, timing, and nursery crop response is ongoing. NP308, Component 1.

4. Accomplishments
1. Biofumigation as an alternative to methyl bromide. Biofumigation with soil-incorporated plant materials has been associated with reduction in soilborne pathogens and diseases. However, little is known about the production of volatile sulfur compounds during decomposition of these plant materials, and even less on their efficacy against soilborne pathogens. A field experiment was conducted by ARS scientists in the Water Management Research Unit in Parlier, CA to determine soil-incorporated white mustard as a green manure crop on controlling soilbore pathogens and nematodes. Fusarium oxysporum counts were significantly reduced after soil incorporation of white mustard and no control was found for Pythium spp. Soil populations of citrus nematodes were reduced and freeliving nematode populations increased after soil incorporation of white mustard. The study demonstrated measurable production of volatile methyl sulfide and dimethyl disulfide gases, the beneficial impact of biofumigation on controlling soilborne pathogens, and potential for alternatives to methyl bromide. NP308 Methyl Bromide Alternatives Component I: Pre-plant Soil Fumigations Alternatives Problem Statement: IA and ID

2. Proper irrigation can reduce fumigant emissions without reducing soil gaseous fumigant concentrations. Emission reduction is required from soil fumigation to improve air quality and adequate fumigant concentrations are needed for pest control. ARS scientists in the Water Management Research Unit in Parlier, CA demonstrated that water seals applied to soil columns following fumigant injection significantly reduced emissions for different textured soils (e.g., loamy sand, sandy loam and clay loam) without reducing fumigant concentrations in the soil profile. We also demonstrated that increasing soil water content prior to fumigant injection significantly reduced emission peaks, which would minimize acute human exposure risks to workers and bystanders. Comparing to plastic tarps, irrigation is a low cost technique for reducing fumigant emissions, and it is especially appealing for commodities with low-profit margins in meeting environmental regulations on emission reductions. NP308 Methyl Bromide Alternatives Component I: Pre-plant Soil Fumigation Alternatives Problem Statement: IB and ID

3. Virtually impermeable film can effectively reduce fumigant emissions in field applications. There have been uncertainties on whether low permeable tarps such as virtually impermeable film (VIF) can reduce fumigant emissions in large field applications. ARS scientists in the Water Management Research Unit in Parlier, CA demonstrated that VIF can significantly reduce fumigant emissions when fumigant was drip applied to raised-beds in large strawberry fields. VIF provides a technology for reducing emissions and offers a feasible method on emission control from fumigation for high-valued crops. NP308 Methyl Bromide Alternatives Component I: Pre-plant Soil Fumigation Alternatives Problem Statement: IB and ID

4. Low application rate of manure can not significantly reduce fumigant emissions. Organic material amendment to soil has shown effectiveness in fumigant degradation and reducing their emissions in lab studies. ARS scientists in the Water Management Research Unit in Parlier, CA determined under field conditions that soil amendment with composted manure with normal application rates is unlikely to be effective to reduce emissions. Much higher organic amendment rates may be required to achieve significant emission reductions in field applications. The conclusion was made based on one field trial data. The results provided information for developing other effective and practical field methods for controlling fumigant emissions. NP308 Methyl Bromide Alternatives Component I: Pre-plant Soil Fumigation Alternatives Problem Statement: IB and ID

5. Herbicide efficacy and crop safety. Evaluation of emerging new herbicides for weed control requires knowledge and information on potential phytotoxicity on crops. Field trials were carried out to ARS scientists in the Water Management Research Unit in Parlier, CA evaluate herbicide efficacy and crop safety. Unlabeled herbicides dithiopyr provided weed control in perennial crop field nurseries equal to or better than oryzalin with similar crop safety. Pre-emergence rimsulfuron and flumioxazin were safer on prunus rootstock planted as hardwood cuttings compared to seeded rootstock cultivars. The research findings contribute to the overall effort on methyl bromide alternatives for weed control in field nurseries. NP308 Methyl Bromide Alternatives Component I: Pre-plant Soil Fumigation Alternatives Problem Statement: IA and ID

5. Significant Activities that Support Special Target Populations

Review Publications
Qin, R., S. Gao, J.A. McDonald, H. Ajwa, S. Shem-Tov, and D.A. Sullivan. 2008. Effect of plastic tarps over raised-beds and potassium thiosulfate in furrows on chloropicrin emissions from drip fumigated fields. Chemosphere. 72:558–563.

Shrestha, A., B.D. Hanson, K.J. Hembree. 2008. Glyphosate-resistant hairy fleabane(Conyza bonariensis)documented in the Central Valley.Calif. Agric. 62:116-119.

Last Modified: 07/25/2017
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