Evaluation of Non-Fumigant Pesticides as Methyl Bromide Alternatives for Managing Soilborne Diseases and Weeds in Vegetable Production

Non-Technical Summary: Vegetables are significant food and cash crops in Georgia with a farm gate value of approximately $895 million annually. Fresh market vegetable production in Georgia has greatly benefited from the development of a raised bed, plastic mulch vegetable production system (plasticulture). Plasticulture in Georgia depends heavily on the use of methyl bromide fumigation to manage the multitude of pests that are associated with the subtropical climate. Among the most troublesome pests in plasticulture-grown vegetables are the root-knot nematodes, purple and yellow nutsedges, Phytophthora capsici and other soilborne pathogens. With the continuing phase-out of methyl bromide from use in vegetable production worldwide, intensive efforts have been made to develop methyl bromide alternatives. Limited success has been made, however, and the majority of studies to look for methyl bromide alternatives have focused on other soil-applied fumigants. Alternative fumigants may provide some level of control of nematodes, diseases and weeds when combined in a system, but buffer restrictions and rising costs limit their use. Using non-fumigant pesticides eliminates buffer restrictions and potentially reduces input costs compared with fumigants. Non-fumigant nematicides, fungicides and herbicides do provide good suppression of nematodes, soilborne pathogens and weeds, but their efficacy has not been compared directly to fumigants extensively. In this project, several newly available and promising non-fumigant pesticides will be evaluated, in comparison to standard fumigants, to develop alternative approaches for control of weeds, root-knot nematodes and soilborne pathogens in vegetable production. The long-term goal of the project is to develop an integrated system for the management of soilborne diseases and weeds of plasticulture-produced vegetables using non-fumigant nematicides, fungicides, and herbicides as alternatives to chemical soil fumigation. The long-term goal will be addressed with: 1) identifying economically viable non-fumigant pesticides that effectively control weeds and soilborne diseases encountered in plasticulture-grown vegetables in Georgia, and 2) enhancing and assisting implementation of the non-fumigant tactics by growers through large acreage on-farm studies and demonstrations at multiple locations and outreach activities. This mission-oriented project supports Methyl Bromide Transitions program goals to ensure economically viable and environmentally sound alternatives to MeBr are in place for the current 2010 Critical Use Nominations. <P> Approach: 1) Field experiments to evaluate application methods and efficacy of thiazosulfene and other non-fumigant nematicides for control of root-knot nematodes will be conducted. The efficacy of these non-fumigant nematicides will be compared to standard fumigants including methyl bromide and Georgia 3-way (Telone II, chloropicrin, Vapam). The experiments will be conducted on cucumber and bell pepper. Root-knot nematode populations in the soil, root galls caused by root-knot nematodes, and plant growth and yield parameters will be determined. 2) Efficacy and application methods of non-fumigant fungicides will be evaluated in comparison to soil fumigants (methyl bromide and Georgia 3-way) for suppression of soilborne pathogens. The studies will be conducted in experimental field plots and non-fumigant fungicides, including fluopicolide, madipropamid, azoxystrobin and mefenoxam, will be applied through drip tape. These non-fumigant fungicides will be applied alone or in combinations. The effect of the non-fumigants and fumigants on soil populations of Phytophthora capsici and other common soilborne pathogens will be evaluated. 3) Field trials to evaluate the efficacy and application methods of non-fumigant herbicides for control of nutsedge and other common weeds will be conducted. Non-fumigant herbicides, including s-metolachlor, halosulfuron, fomesafen, clomazone and sulfentrazone, will be applied prior to or after transplanting at different rates. The efficacy of the non-fumigant herbicides will be compared to methyl bromide and Georgia 3-way. Weeds to be evaluated will include yellow nutsedge, purple nutsedge, and other common weeds. 4) Field studies will be conducted to develop alternative management strategies integrating the most effective non-fumigant nematicides, fungicides and herbicides. Methyl bromide and Georgia 3-way will be used as controls. Populations of root-knot nematodes and soilborne pathogens in the soil will be enumerated. Root gall indices, incidence of diseases caused by soilborne pathogens, and populations of purple nutsedge, yellow nutsedge, and other common weeds will be determined. 5) The most promising findings from all studies in experimental field plots will be used to conduct on-farm studies and demonstrations. The on-farm studies and demonstrations will be conducted in cooperation with vegetable growers in Georgia. Selected non-fumigant nematicides, fungicides, and herbicides will be used in combinations and conventional standard weed and disease control measures used by the vegetable growers will serve as a control. Cost/benefit analyses will be conducted to determine the management strategies that yield the greatest financial return to the grower. State extension specialists, county extension agents and other project participants will enhance and assist implementation of the alternative approaches by growers through various outreach activities.