DMDS In Combination with Reduced Rates of Chloropicrin for Sustainable Strawberry Production and Soilborne Pathogens Control In California

With the challenges strawberry growers face in the process of replacing methyl bromide (MeBr) while maintaining yield threshold, dimethyl disulfide (DMDS) with its zero Ozone Depletion Potential (ODP) appears to be a promising solution. Dimethyl disulfide DMDS is a yellow solution with strong garlic-like odor. Field experiments were conducted for the growing season of 2009-2010 in Watsonville and Salinas, CA to investigate the efficacy of DMDS with reduced rates of chloropicrin on strawberry yield, soilborne pathogens, and major resident weeds.  Chloropicrin treatments were drip applied with and without sequential application of different rates of DMDS. Beds were tarpped with virtually impermeable film (VIF) for all treatments and with standard polyethylene STD PE for methyl bromide chloropicrin mix (MeBr/Pic). Sequential applications of DMDS took place five days following the primary application. Strawberry plants were transplanted four to six weeks after the sequential applications. The results suggest that DMDS sequential and DMDS/chloropicrin pre-mixed applications can sustain strawberry yields to levels similar to, or in some cases, higher than those obtained by MeBr/Pic standard fumigation. In Watsonville, the sequential application of DMDS at 350 lbs/acre following low rate of chloropicrin 100 lbs/acre produced total and marketable yield 7% higher than MeBr/Pic per plant. Total and marketable yield from all treatments were significantly higher than total and marketable yield from untreated control but were not significantly different from yield by methyl bromide mix. In Salinas, the pre-mixed application of DMDS at 350 lbs/acre and Pic at 100 lbs/acre produced marketable yield was 2% higher than yield produced by MeBr/Pic and produced total yield equivalent to yield produced by methyl bromide mix. In pathogens control, DMDS was found effective against verticillium dahliae and pythium ultimum. At planting and at harvest in Salinas, DMDS provided 100 percent control over verticillium, which was similar to MeBr/Pic.  At planting in Watsonville, pre-mixed DMDS at 350 lbs/acre and pic at 100 lbs/acre controlled pythium by 88.5% comparing 95.9% by MeBr/Pic. Therefore, DMDS can be a promising alternative to MeBr with high efficacy and efficiency because of maintaining threshold yield and providing effective control against two major soilborne pathogens. Meanwhile, DMDS enabled the use of lower rates of Pic, which potentially reduces buffer zones, and hence, contributes to profitability. The use of DMDS can be counted as a step toward sustainable production by meeting the demands on higher yields while using resources that have minimum impact on environment and human.