CONVENTIONAL AND ORGANIC ALTERNATIVES TO METHYL-BROMIDE ON CALIFORNIASTRAWBERRIES

A study was conducted in a commercial strawberry planting on the Calif ornia central coast to evaluate the relative efficacy of chemical and organic alternatives to methyl bromide fumigation. The three chemical alternatives included Telone/Chloropicrin 70/30, Basamid, and Metam so dium. Organic alternatives included addition of broccoli residues, spe nt mushroom compost, and a combination of both broccoli and spent mush room compost. AU treatments were compared to standard methyl bromide/c hloropicrin 75/25. Weeding costs were five-fold greater in organic tre atments than in chemical fumigant treatments and were not statisticall y different from untreated controls. The weed species in the organic t reatments were significantly different than in the untreated or the ch emical fumigant treatments, suggesting that these weeds were in the ad ded organic material. Strawberry yields were highest in the methyl bro mide/ chloropicrin, Basamid and Telone/chloropicrin treatments. Strawb erry yields among the organic treatments were not statistically differ ent from the untreated control. Soil microbial biomass measurements an d strawberry root pathology indicated that a single application of the se particular organic amendments were inadequate in significantly incr easing soil food web diversity on this previously fumigated soil to a point where strawberry pathogens could be suppressed to commercially a cceptable levels. These results suggest that previously fumigated soil that has been depleted of Vesicular Arbuscular Mycorrhizal (VAM) fung al colonization and other beneficial microbiota require additional rec onditioning before the soil would be suitable for commercial strawberr y production, given the highly pathogen susceptible cultivars commonly grown in California.