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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

2011 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
Evaluation of pathogen control by methyl bromide alternatives were made in field trials in grower cooperator fields. Ornamental crop field trials using steam and dimethyl disulfide (DMDS) as methyl bromide alternatives were conducted in Oxnard, CA. Multiple soil assays from the DMDS field and a micro plot experiment were completed. An ornamental crop field trial on methyl bromide alternatives using chloropicrin and 1, 3-dichloropropene and low-permeable tarps was initiated in Moss Landing, CA. Pathogen assays of soil samples from the Watsonville field site and a greenhouse trial for a soilless substrate strawberry project were completed and results were compiled. A study on the etiology of the root rot disease of calla lily was initiated in the Moss Landing area. Pythium spp. isolates were collected from diseased calla lily roots from production fields. The isolates were tested for pathogenicity in a greenhouse assay and the pathogenic isolates were molecularly evaluated by polymerase chain reaction (PCR) and restriction enzyme digestion profiles to determine identity. Nematode control and crop response were measured from three ongoing grape replant fumigation field trials. Soil samples were collected from 5-60 cm depth from each treatment plot and analyzed for type and number of resident nematodes. Because the fumigation treatment was applied in 2008-2009, grape yield was measured as a crop response variable for the three field trials. Nematode control and crop response were also measured from the post plant DMDS trial on grapevines. Soil samples were collected from each DMDS treated plots (and the untreated control plots) and analyzed for nematode species and densities. Crop response measurements included yield and stomatal conductance from the grapevine leaves to determine the health or potential phototoxicity effect on the vines. Three field trials were conducted from fall 2010 through June 2011. The potential for reducing fumigant emissions and improving pest control efficacy was determined using a totally impermeable film (TIF) tarp at reduced fumigation rates. The first trial was conducted in California and determined the effect of reduced rates under TIF on fumigant soil distribution and efficacy against nematodes, pathogens and weeds in a perennial fumigation setting. The second trial was conducted in Florida in a raised-bed field prior to planting tomato and tested the combination of carbonation and TIF use on fumigant emissions and fumigant concentration changes in soil. The third trial was conducted in California in an 8-acre field covered with TIF and measured fumigant soil distribution, emission, and movement at tarp-edge areas. Sample analyses and data compiling were completed for first two trials and are on-going for the third trial.

4. Accomplishments
1. Dimethyl disulfide (DMDS) as a methyl bromide alternative for pathogen control. DMDS is a potential methyl bromide alternative for pre-plant soil fumigation; however, limited data are available for its efficacy in pathogen control. ARS scientists in Parlier, CA, in a sunflower field trial in Oxnard, CA, found that pathogen densities of Fusarium oxysporum were reduced by 94% with methyl bromide (MB) compared to 80% with DMDS. Pythium spp. was reduced by 99% with MB compared to 98% with DMDS. Verticillium dahliae was reduced by 60% with MB and 94% with DMDS. Neither fumigant controlled Phytophthora cactorum. The research generated important data which demonstrated that control of soil-borne pathogens by the two fumigants was dependent on the target organism, and DMDS has efficacy for the control of soil-borne pathogens for the production of cut flowers on the central coast of California.

2. Etiology of calla lily root pathogen. There is a lack of understanding of genetic composition of soil pathogens in ornamental crops. Field and a greenhouse studies were conducted by ARS scientists at Parlier, CA where 39 isolates of Pythium spp. were recovered from diseased roots of calla lily form multiple locations in production fields and tested for pathogenicity in a greenhouse test. All the pathogenic isolates were molecularly characterized by PCR amplification and restriction enzyme digestion of the Cyclooxygenase-1 & 2 genes. Thirty-five of the isolates were pathogenic and expressed the same genotype; the non-pathogenic isolates had different genotypes. These data suggest that the pathogens from these multiple locations were identical. The identity of the pathogen is still being investigated, but it may be a never before identified species. Effective management requires knowledge of the pathogen complex.

3. Nematode control with reduced rates of Telone C35 under totally impermeable film (TIF). Replanting of perennial orchards and tree and vine nurseries in California depend on soil fumigation for production and delivery of nursery crops free of economically important plant parasitic nematodes as required under the California Department of Food and Agricultural’s Nursery Stock Nematode Control Program. ARS scientists in Parlier, CA, conducted field trials in 2009-2010 to test nematode control under TIF using reduced application rates of Telone C35. The efficacy of both full and half rates of Telone C35 in the fall 2009 trial was 100% against citrus nematodes and pin nematodes at soil depths up to 90 cm. In the fall 2010 trial, the efficacy on citrus nematodes at 15 cm soil depth was 100% under TIF and 95% under the standard high density polyethylene (HDPE) when only one quarter rate of Telone C35 was applied. Also in the 2010 trial, 100% efficacy was found for root-knot nematodes at 90 cm soil depth. These results indicate that lower (than the label rate) fumigation rates can be used, under TIF, without compromising the nematode control efficacy.

4. Fumigant emission reduction under totally impermeable film (TIF). TIF was shown to prevent fumigant penetration in the laboratory, however, no reliable field data supports the claim. Field tests were conducted by ARS scientists in Parlier, CA to determine the ability of TIF for reducing fumigant emissions. The TIF tarp reduced 1,3-dichloropropene emissions to as low as 0.1% of applied amount in a field trial conducted in spring 2011. Greater than 90% emission reduction was obtained in an earlier trial from broadcast fumigation. Surging emission upon tarp-cutting is a concern, which was addressed in the most recent June 2011 field trial in California. The research generated important data which will assist regulatory agencies in developing regulations on the safe use of TIF tarp.

5. Enhanced fumigant soil concentration and pest control under totally impermeable film (TIF). TIF is claimed to retain fumigant gases in soil yet data are not available on the increased resident time when TIF is used under field conditions. A field trial was conducted by ARS scientists in Parlier, CA in fall 2010 to determine improved pest control efficacy for perennial crops. Treatments included TIF and the standard high density polyethylene (HDPE) tarp in combination with different fumigation rates (full, half, and quarter rate) of Telone C35. Fumigant retention time and soil concentration increased, under TIF, which resulted in higher soil concentration-time exposure indices than that under the HDPE. This led to 100% pest control on nematodes and pathogens under either full or half rates of Telone C35 under TIF. Results indicate that TIF has the potential to offer a long-term solution for reducing environmental impact of soil fumigation and improving efficacy.

6. Weed control using dimethyl disulfide (DMDS) and reduced rates of Telone C35 under totally impermeable film (TIF). DMDS is a potential methyl bromide alternative chemical and TIF is a potential replacement for the standard high density polyethylene (HDPE) for pre-plant soil fumigation, however, limited data are available on weed control. ARS scientists in Parlier, CA in a sunflower field trial in Oxnard, CA fumigated with DMDS and lower weed densities (37.0/m2) were found compared to methyl bromide plots (51.5/m2) or the untreated control (127.5/m2). In a Telone C35 trial in Parlier, CA plots covered with TIF tarp under full rate resulted in the lowest weed biomass, followed by TIF-half rate and HDPE-full rate. The highest weed biomass was from the non-fumigated control and the HDPE-half rate had a weed biomass as high as the control. DMDS has efficacy for the control of weeds and reduced fumigation rates can be used for weed control under TIF.

Review Publications
Gao, S., Hanson, B.D., Qin, R., Wang, D., Yates, S.R. 2010. Comparisons of surface sealing methods in emission reduction from soil fumigation using field plot tests. Journal of Environmental Quality. Available on line: Nov 2010, doi:10.2134/jeq2009.0422.

Cabrera, A., Wang, D., Schneider, S.M., Hanson, B. 2011. Effect of potential methyl bromide alternatives on plant parasitic nematodes and grape yield under vineyard replant conditions. American Journal of Enology and Viticulture. 62(1):42-48.

Gao, S., Hanson, B.D., Wang, D., Browne, G.T., Qin, R., Ajwa, H., Yates, S.R. 2011. Methods evaluated to minmize emissions from preplant soil fumigation. California Agriculture. 65(1):41-46.

Wang, Q.X., Wang, D., Tang, J., Wei, S., Yan, D.D., Zhang, H., Wang, F.Y., Guo, M., Cao, A. 2010. Distribution and emission of chloropicrin applied as gelatin capsules. Journal of Environmental Quality. 39:917-922.

Wang, D., Gao, S., Qin, R., Browne, G.T. 2010. Lateral movement of soil fumigants 1,3-Dichloropropene and Chloropicrin from treated agricultural fields. Journal of Environmental Quality. 39:1800-1806.

Hanson, B., Gao, S., Gerik, J.S., Shrestha, A., Qin, R., Mc Donnald, J.A. 2011. Effects of emission reduction surface seal treatments on pest control with shank-injected 1,3-dichloropropene and chloropicrin. Crop Protection Journal. 30(2):203-207.

Qin, R., Gao, S., Ajwa, H., Sullivan, D., Wang, D., Hanson, B.D. 2011. Field evaluation of a new plastic film (Vapor SafeTM) to reduce soil fumigant emission and improve distribution in soil. Journal of Environmental Quality. 40: 1195-1203.

Last Modified: 06/23/2017
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