An official website of the United States government.
The goal of this project is to develop a non-fumigant based system using a combination of solar and steam heat, or humid hot air to kill soil-borne pests in flower and strawberry fields. <P>Specific objectives: <ol> <LI> Evaluate solarization plus steam and the Verdivap Airstream humid hot air applicator for soil disinfestation efficacy on soilborne pests. <LI> Evaluate crop yield and quality, resulting from soil disinfestation with heat from solarization and steam, and humid hot air, compared to methyl bromide fumigation. <LI> Demonstrate the solarization plus steam and humid hot air soil disinfestation techniques to growers in commercial flower in California and Florida and strawberry fields in California. <LI> Conduct economic analysis of solarization plus steam and humid hot air soil disinfestation to determine if it is commercially viable.
Non-Technical Summary: California and Florida flower and strawberry producers are large consumers of methyl bromide (MB). Proposed buffer zone regulations would preclude fumigant use in many flower and strawberry fields. Conversion from MB to alternative fumigants is hindered by regulatory limits in both states. Reduction in MB use would be more feasible with viable nonfumigant disinfestation systems. Steam has long been used to control soil pests in greenhouse soils. However, field steam disinfestation has been limited due to difficulty in treating large areas with existing steam applicators and high energy costs for steam generation. Steam injection from a portable steam generator into planting beds would allow growers to supplement solar heat (solarization) with steam heat. Our preliminary data suggests solarization combined with steam reduces the energy needed for soil steaming. Hot humid air for soil disinfestation has lower energy costs per acre than steam, and we propose to evaluate a commercial hot humid air applicator. The project objective is to develop and demonstrate an economically feasible commercial-scale heat disinfestation system for field-grown flowers and strawberries. This goal is compatible with the Methyl Bromide Transitions program objective to develop economically viable environmentally sound alternatives to MB. We propose to inject steam into distribution lines installed in flower or strawberry beds and heat the soil to 70?C for 20 minutes, or to use a hot humid air applicator to disinfest soil. <P> Approach: Field studies will be conducted to find the optimal combination of solarization and steam or humid hot air to control soil pests in flower and strawberry. Raised beds will be established and prepared as a finished seed beds with starter fertilizer and drip irrigation tape installed. Steam distribution will be conducted with either plastic pipe buried in the bed or injected from hoses installed on the beds with hollow spikes that inject steam into the bed. The steam will heat the top 12 inches of the bed. The steam lines will be spaced 12-in apart with 10-inch spacing between steam emitters. Humid hot air will be applied to the soil prior to bed formation as per manufacturer specifications. Pathogen and weed seed samples will be installed in the planting beds prior to tarp installation. Briefly, standard bioassay techniques will be used with weed seed enclosed in nylon mesh bags. Weeds to be included in the bioassay are: common chickweed, common knotweed, common purslane little mallow, and yellow nutsedge. Flower bulbs enclosed in mesh bags will be included in the flower studies to determine if the experimental treatments can control volunteer bulbs. After removal from the field plots, bulb viability will be assessed by planting in pots and counting the number of bulbs that sprout. Weed control will be determined by periodic weed harvest and fresh weight measurement. Data will be subjected to analysis of variance. Bioassay samples of Verticillium dahliae will be prepared in the laboratory, incorporated into autoclaved field soil and placed individually in gas permeable nylon mesh bags. Bags will be buried at 6, 12 and 18 inches below the soil surface prior to treatments and then retrieved afterwards. Standard baiting techniques and/or dilution plating to appropriate selective media will be used to assess viability of each pathogen before and after treatments are applied. The percent reduction in propagules of the various pathogens and the severity of naturally occurring disease outbreaks during the growing season will be subjected to analysis of variance. Temperature recording probes will be installed in the beds at depths of 2, 6, 12 and 18 inches and temperatures will be monitored continuously during the solarization and steam disinfestation process. After the bed has been prepared, clear plastic mulch will be installed and then the beds will be irrigated to bring the soil moisture to sufficient levels for proper heat conduction and solarization.