Evaluation and Demonstration of a Mobile Steam Applicator to Disinfest Soil in Field-Grown California Strawberry and Flower Production

Steam can effectively kill soil borne pests if soil temperatures can be raised to 70 °C for 20 min. The Ferrari Sterilter is capable of generating super heated steam to reach these temperatures within 5 to 7 min. Frontal plates on the machine allow it to thoroughly heat the soil to 30 cm depth, granting homogeneous soil disinfestation. In Nov-Dec. 2009, demonstration trials were initiated at a commercial strawberry site at Salinas, CA, and a cut flower nursery site at Carlsbad, CA, to evaluate the Sterilter under field production systems and to demonstrate its operation to the growers. Local growers and few industry representatives were present during treatment application. Soil at both sites was worked with a rototiller after which steam was applied to the soil with the Sterilter for a period of 6 min. At Salinas, total area treated with steam was sufficient for five raised beds that were each 30.5 m long and 1.4 m wide. The neighboring five beds remained untreated. Temperatures during the steaming process were recorded using temperature probes installed at 8-, 15-, and 30-cm depths. Strawberry variety ‘Albion’ was planted on 24 Nov. 2009. Steam treatment did not injure strawberry plants. Weed density counts were taken along the entire length of the bed and initial weed density counts on steam treated plots were 76% lower than untreated control. Strawberry plants in the steam treatment had 4% larger canopy diameters than untreated plots. At Carlsbad, the study was arranged in a completely randomized design. Seven plots 15 m long and 2 m wide were steam treated and five plots remained untreated. Permeable nylon mesh bags containing soil infested with citrus nematode and other free living microorganisms were buried at 15 and 30 cm in the center of the plots prior to treatment, and removed one day after treatment. Beds were seeded with Ranunculus on 5 Jan. 2010. At 15 cm depth, the citrus nematode and free living microbial population was significantly reduced in steam treated plots compared to untreated plot at α = 0.05. At 30 cm depth, only the free living microbial population was reduced in steam plots. Operation costs for the Sterilter in Nov. 2009 were determined to be $3848 per acre. We will continue to monitor the weed data and will determine crop yield at both locations. Results will be presented to growers and industry representatives at field days in June 2010.