Steam and Solarization to Disinfest Soil In California Strawberry and Cut-Flower Production

With the phase-out of methyl bromide in California agriculture, there’s an immediate need to evaluate and adopt feasible alternatives. Although solarization can effectively kill soil-borne pests, the presence of fog and cool summer temperatures in Coastal California cause it to be a less reliable tool for pest control than chemical fumigation. The objective of this study was to evaluate steam in combination with solarization for effective pest control in field-grown strawberry and cut-flower production. Field studies were conducted at the Spence Research Farm at Salinas, CA (strawberry) and at a commercial farm (cut-flower) at Prunedale, CA in 2007-08 and 2008-09 seasons. Plot beds were 1.3 to 1.8 m by 6.1 m long. Prior to treatment application, pathogen and weed seed samples were enclosed in permeable nylon mesh bags and buried in experiment beds. Pathogen samples were buried at 45, 30 and 15 cm depth and weed samples at 15 and 5 cm depth. These samples were removed post-treatment and their viability determined using petri-dish assays for pathogens, and tetrazolium tests for weed seeds. Experimental design was a randomized complete block replicated six times. Treatments in the study included 67% methyl bromide + 33% chloropicrin (MBPic, 67:33) at 392 kg.ha^-1, control, solarization, steam, and steam + solarization. For steam + solarization treatments, beds were solarized two weeks prior to steam application and two weeks after steam application. Prior to application of clear tarp for solarization, beds were irrigated to bring soil moisture to sufficient levels to promote heat conduction. Steam was injected for sufficient time to raise the bed temperatures to 70 C for 20 min. After 20 min., steam disinfestation was discontinued. Temperatures during steam and solarization process were monitored using temperature probes installed in beds at 45, 30, 15, and 5 cm depths. The amount of fuel, time and labor needed for treatment application were recorded. At the end of 4 week treatment period, strawberry and cut-flower were transplanted. Periodically through the growing season, weed density, weed fresh biomass and hand weeding times were recorded. In comparison to MBPic, solarization alone was not effective in controlling weeds, or reducing the hand weeding time. Steam with or without solarization resulted in weed control similar to MBPic. In comparison with control and solarization alone, steam treatments with and without solarization were sufficient to control Verticillium. First year strawberry yields in steam treatments were comparable to MBPic.