Use of Natural and Synthetic Isothiocynates as Alternatives to Methyl Bromide for Pest Suppression in Vegetables

Non-Technical Summary: Methyl bromide is used extensively in tomato and pepper production in the Southeast, mainly to control nutsedge species and to a lesser extent, soil-borne pathogens, nematodes, insects, and other weeds. The Methyl Bromide Critical Use Nomination packet for U.S. grown tomato and peppers projects 89 and 96% of the methyl bromide requested for these crops will be used in the Southeast. The overall goal of this project is to address the need of alternatives to methyl bromide through the discovery and demonstration of effective, efficient, and economical pest suppression using natural isothiocyanates produced by Brassicaceae plants and synthetic isothiocyanates. <P> Approach: Obj. 1. Brassicaceae cover crops will be seeded in the fall. Cover crop biomass will be harvested and separated into roots and shoots prior to terminating the cover crops in the spring. Plots will be tilled and tarped with VIF mulch. A tissue sample from each plot will be analyzed for GSLs. Another sample will be frozen to determine the maximum release of ITCs from disrupted tissue. ITCs in soil will be quantified prior to incorporating the residues; 1 and 8 hr after amendment; and 1, 4, 7, and 14 d after amendment. Additional sampling will occur if ITCs are detected at 14 d. After the final sample, holes will be placed in the plastic to allow emergence of weeds not controlled by the ITCs produced by the cover crops. Weed emergence and biomass will be quantified after 4 wks. Obj. 2. The three most promising cover crops from Obj. 1. will be further evaluated. Tomato and bell pepper will be transplanted into 60 ft long plots, with one-half of each plot weeded once every two weeks to determine the time required for weeding each cover crop treatment. These data will be used in the economic analysis for each cover crop. The remaining portion of each plot will be visually rated for weed control and crop vigor. Additionally, plots will be scouted and insecticides and fungicides applied to experimental treatments as needed based on economic threshoulds. Differential costs of inputs versus returns will be calculated based on actual data from each treatment. Obj. 3. The effectiveness of 3-methylthiopropyl and phenyl ITC will be evaluated using drip chemigation in tomato and a broadcast spray application beneath plastic mulch in pepper. The experiment will be a split plot with main plots being mulch type and subplots being a factorial arrangement of two ITCs and five ITC rates. A standard treatment of methyl bromide plus chloropicrin will be used for comparison. Plots will be monitored for insects and diseases and experimental treatments will only be sprayed once an economic threshold is reached. Marketable fruit will be harvested and graded. Weed emergence will be monitored in the opening adjacent to the base of the crop. Nutsedge emergence through the plastic mulches will also be assessed. Weeds will be harvested following crop maturity and biomass production quantified. Soil cores will be removed from the beds following crop maturity to quantify the number of viable propagules in the soil. Exhaustive germination will be used to quantify viable propagules of weeds in each plot. Obj. 4. Recommendations will be developed for tomato and pepper producers and published in "Vegetable Crop Guidelines for the Southeastern US". A presentation will be made at the Southeastern Eastern Vegetable Extension Workers meeting to vegetable specialists. Registration of the effective ITCs will be requested through the IR-4 program. Efficacy ratings will be developed for the ITCs on the weeds in each trial and this information made availabe to growers on a website created and devoted to weed management recommendations for the Carolinas. A workshop to familiarize extension agents, producers, and CCAs with biofumigation facts and techniques will be presented.