Alternatives to Reduce Soil Fumigant Use in Key California Crops: A Meta-Analytic Approach.

Alternatives to reduce soil fumigant use in key California crops: A meta-analytic approach Michael L. Grieneisen, Huajin Chen, Yu Zhan, Jonathan Ackerman, Minghua Zhang Department of Land, Air & Water Resources, University of California, Davis, CA 95616 Over 40,000,000 lbs of pre-plant soil fumigants were used in CA in 2012, primarily on strawberry, carrot, tomato, potato, almonds, walnuts and grapes. Due to the volatility and acute toxicity of current fumigants, various stakeholders around the world are searching for viable alternatives which can effectively manage soil-borne pathogens & weeds in these crops. This study examines the global literature on non-fumigant pre-plant soil treatments (i.e. solarization, steam or heat treatment of soil, chemicals other than the current dominant fumigants, compost, cover crops/crop rotation, pathogen-resistant varieties, and soil-less culture) in these crops to determine whether the weight of evidence suggests that they may be truly viable alternatives to the current chemical fumigants. Various peer-reviewed and gray literature sources yielded ~1,600 potential publications, of which 260 were retained after a multi-tiered screening process. Data which compared the yield or pathogen suppression obtained with 954 distinct non-fumigant treatments to both fumigant treatments and untreated controls (UTC) were extracted. Yields for experimental treatments were normalized by dividing by the yield of the UTC. The weight of evidence suggests that solarization, steam, or soil treatments with dimethyl disulfide, isothiocyanates or propylene oxide are the most efficacious of the alternative management practices, though each has caveats in terms of cost or other externalities. It is not clear whether adding Brassica plant material (a potential source of isothiocyanates) or other enhancements improves yields obtained with traditional solarization treatments. Various deficiencies in the current state of knowledge. So future studies should include more comprehensive data on the full spectrum of relevant weeds and pathogens.