Integrated soil-borne disease and weed management for organic strawberries using anaerobic soil disinfestation, broccoli residue incorporation and mustard cake application

Summary

Investigator: Carol Shennan, University of California, Santa Cruz, Center for Agroecology and Sustainable Food Systems
Stakeholders: Organic strawberry producers

Continued growth of organic strawberries in California faces two major challenges: soil-borne disease management without chemical fumigants and rising costs for weeding. Verticillium wilt, cause by Verticillium dahliae, is very difficult to control in organic strawberry systems due to the pathogen’s wide range of host crops, its overwintering structure, and current strawberry cultivars’ high sensitivity to the disease. Anaerobic soil disinfestation (ASD) was developed in the Netherlands and Japan as an ecological alternative to methyl bromide fumigation. ASD integrates principles from solarization and flooding for fields where these methods are unfeasible or ineffective.

With funding from the USDA methyl bromide transition program, we have conducted a series of experiments for optimizing ASD to California strawberries for the last three years, with promising results. Integrating ASD with broccoli residue incorporation and mustard cake application, the goal of this project is to demonstrate the effects of these practices on soil V. dahliae population, weed biomass and fruit yield in organic strawberries in coastal California.

The idea of this project began when the researchers were approached by two collaborative organic growers: a small-scale diversified organic grower who has had multiple outrbreaks of Verticillium wilt in strawberries after 30 years of organic production, and a large-scale grower who has fields highly infested by V. dahliae. Using fields with high Verticillium wilt pressure, we will conduct replicated split-plot experiments with broccoli and untreated control as main plots, and ASD, mustard cake, ASD plus mustard cake and untreated control as split plots at two working organic farms in Santa Cruz and Salinas.

Specific project objectives are to demonstrate the effects of anaerobic soil disinfestation, broccoli residue incorporation, mustard cake application, and a combination of all three on Verticillium dahliae suppression, weed suppression and strawberry fruit yield. Measurements between treatments and untreated control will include marketable fruit yield, levels of V. dahliae in soil and wilt symptoms on plants, difference in weeding time, and estimated income using fruit yield data, weeding time, input costs and operational costs.

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