Optimizing Anaerobic Soil Disinfestation for Non-Fumigated Strawberry Production in California

Soilborne disease management without use of chemical fumigants is a major challenge in California strawberry production. Anaerobic soil disinfestation (ASD) was developed in the Netherlands and Japan as an ecological alternative to methyl bromide fumigation. ASD involves incorporating an organic carbon source, irrigating to saturate the soil and then covering the soil with a plastic tarp to stimulate anaerobic decomposition of the organic carbon. The byproducts of anaerobic decomposition have proved toxic to many fungal pathogens and nematodes.  The goal of this project is to optimize ASD for strawberry production in coastal California.  We conducted a series of pot and then field experiments to test the efficacy of ASD across varying soil types, carbon sources, and seasons. Pot experiments showed that a) wheat bran, rice bran, mustard cake, grape pomace and ethanol all reduced V. dahliae propagules when used as a carbon source for ASD, and b)that cumulative reducing conditions of 50,000 CumEh mVhr (below 200mV) are needed for effective reductions in V. dahliae propagules. Eh reduction near or exceeding 50,000 CumEh mVhr by ASD was observed in replicated field experiments in Ventura (2009) and Watsonville (2009-10).  88% and 54% reduction in native V. dahliae populations in soils was found in ASD plots in Salinas (2008-09) and Ventura (2009), respectively. Strawberry fruit yield in ASD plots in Moss Landing site with very low V. dahliae pressure was comparable with untreated check and surrounding methyl bromide treated field showing there is no carry over of toxicity of ASD  to strawberry plants. Field experiments in Watsonville, Salinas, and Ventura are being repeated (with appropriate modifications) with the growers who are interested in ASD.