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Methyl bromide is a key tool for managing weeds and the soilborne pathogen, Phytophthora capsici, in vegetable crops in Michigan and in other U.S. regions. This pathogen has spread and raising crops susceptible to P. capsici has become an overwhelming challenge. The U.S. Critical Use Nomination (C.U.E.) for cucurbits and peppers acknowledges P. capsici as a target pest for which methyl bromide is needed.<P> A Vegetable Methyl Bromide Taskforce including plant pathologists, horticulturalists, an economist, and growers has developed the proposed objectives and will steward the implementation of the research advances from this project. <P>Our goal is to develop a plan for Michigan's fresh market cucurbit and pepper growers to reduce methyl bromide emissions and increase the use of methyl bromide alternatives. This will be accomplished through testing potential fumigant alternatives to methyl bromide to determine whether they are: a) effective against P. capsici and commonly occurring weeds, b) economically beneficial, and c) easily integrated into production systems. <P>Grafted plants represent a novel, non-fumigant method to control P. capsici and will also be tested. Large scale trials will be conducted with grower cooperators to examine various fumigants, virtually impermeable film, and grafted plants. <P>Planned extension activities include demonstration field plots, irrigation scheduling, field meetings, reporting sessions with growers, packers and consultants, newsletters, and formal educational programs. Michigan and other regions that list P. capsici as a basis for their C.U.E. will benefit from this project by using the developed disease management recommendations to become less reliant on methyl bromide. We will accomplish this through the following specific objectives.<OL> <LI> LPDE and VIF plastic mulches: Compare the efficacy of fumigants applied under LDPE and VIF mulches for control of P. capsici and commonly occurring weeds affecting cucurbits and peppers. Research has shown that certain fumigant alternatives can be more effective if sealed into the soil with the use of VIF. <LI>Grafted plants for disease resistance: Assess the potential for grafting cucurbits onto resistant rootstocks to overcome the root and crown rot phase of P. capsici. Limiting the ability of the pathogen to reproduce on roots and lower stems of the rootstock will reduce the below-ground and above-ground phases of disease. A direct outcome of this research will be a biological and economic assessment of the merit of grafted cucurbits as an alternative to methyl bromide.<LI> Economic assessment: Determine if technically feasible alternatives to methyl bromide are economically viable, and provide an economic assessment that can be used to support Critical Use Exemptions. <LI> Extension efforts: Disseminate results through intensive contact with agents and farmer groups, field research and demonstration plots with grower cooperators, and through newsletters and meetings.
Non-Technical Summary: Methyl bromide is a key tool for managing weeds and the soilborne pathogen, Phytophthora capsici, in vegetable crops in Michigan and in other U.S. regions. Phytophthora has spread and become an overwhelming challenge because it can infect a wide variety of crops, can persist in agricultural soils for a long time and has swimming spores that spread easily by water. Given the phase-out of methyl bromide in 2005, it is imperative that growers of these crops identify effective and cost-effective alternatives. Our goal is to develop a plan for Michigan's fresh market cucurbit and pepper growers to reduce methyl bromide emissions and increase the use of methyl bromide alternatives. This will be accomplished through testing potential fumigant alternatives to methyl bromide to determine whether they are: a) effective against P. capsici and commonly occurring weeds, b) economically beneficial, and c) easily integrated into production systems. Grafted plants represent a novel, non-fumigant method to control P. capsici and will also be tested. Large scale trials will be conducted with grower cooperators to examine various fumigants, virtually impermeable film, and grafted plants. Planned extension activities include demonstration field plots, irrigation scheduling, field meetings, reporting sessions with growers, packers and consultants, newsletters, and formal educational programs. <P> Approach: OBJECTIVE 1 (LDPE and VIF plastic mulches): Fumigants, methyl bromide and an untreated will be tested on cucurbits and peppers in plots with 2 mulch treatments set up in a randomized complete block design replicated 3 times. Cucurbit and pepper transplants will be hand planted into plots and grown using normal practices. Weekly crop stand counts, vigor ratings, disease incidence and rating, date to harvest, fruit quality, and yields will be taken. Before and after fumigation, the germinable weed seed bank of composite soil samples will be estimated using a greenhouse method. Prior to and after fumigation, viability of weed seeds (50 of 2 species) buried in nylon mesh bags will be assessed with GA3 and tetrazoleum assays. Weed density in planting holes or through plastic will be evaluated at 3 and 6 weeks after planting, and prior to crop harvest, when above-ground weed biomass will be determined and the 2 most abundant weed species assessed separately. Soil will be sampled for detection of P. capsici before fumigation, at planting, midseason, and at harvest. Cores (12 inches) will be divided into 6-inch increments and plated onto semi-selective culture media. Identification of isolates will be confirmed morphologically and by polymerase chain reaction (PCR). A commercialized soil extraction kit or published protocols will be compared/modified for P. capsici detection directly in the soil. Samples will be used for development of real-time PCR. OBJECTIVE 2 (grafted plants for disease resistance): Years 1-2: Grafted seedling lines (5) will be compared to the nongrafted standard plants in a randomized block design replicated 4 times. Year 3: promising grafted lines will be compared to a susceptible cultivar in a larger trial replicated 3 times. Plants will be evaluated for stand counts, plant vigor, total, and marketable yield. OBJECTIVE 3 (economic assessment): Alternatives will be evaluated for profitability within Michigan's marketing environment. Trials will be evaluated to determine each alternative's potential revenue-generating ability and the quality/grade and harvest timing of the crops. The effects of different production practices on costs will be determined. OBJECTIVE 4 (extension efforts): Research results will be disseminated through intensive contact with grower cooperators and farmer groups, and through newsletters, meetings, and field plot tours. Articles will be published in peer-reviewed journals. Selected growers will be enrolled in the Southwest Michigan Irrigation Network. Sites will be monitored weekly and growers will receive a FAX with soil moisture data and irrigation recommendations demonstrating that water use and disease risk can be reduced while maintaining yields.