Alternative to Soil Fumigation: Sealing Soil Amended with Cover Crop Residues Containing Biotoxic Volatile Compounds

James J. Stapleton, UC Statewide IPM Project
Kearney Ag. Center, 9240 S Riverbend Ave, Parlier CA 93648

With increasing regulatory restrictions on soil fumigation chemicals, agricultural producers must find other strategies for overcoming soilborne diseases and pests. One emerging possibility is incorporation of cover crop residues which produce biotoxic degradation products. Biocidal activity of these products can be expected to increase when used in conjunction with a soil sealant such as plastic tarping, and with soil heating. Recent studies were done with a combination of cruciferous residues and soil solarization to test improved pathogen control, and to determine qualitative and quantitative relationships of soil heating and sealing on concentrations of biotoxic volatile compounds generated in treated soil. Results showed that the residues alone sometimes had a moderate fungicidal effect on Pythium ultimum and Sclerotium rolfsii; solarization alone was more effective; and the combination provided the greatest numerical effect. Heated cabbage-amended soil generated a wide range of volatile compounds, including alcohols, aldehydes, sulfides, and isothiocyanates. The levels of isothiocyanates and aldehydes generated in heated soil were significantly correlated with reduced numbers of the two test fungi. According to current regulations, use of cover crop residues, even when intended for pesticidal activity, do not carry regulatory requirements when produced on-farm. We are working to develop a library of "customized" soil amendments which will have greater effect on specific pest organisms.

Reference: Gamliel, A., and Stapleton, J.J. 1993. Characterization of antifungal volatile compounds from solarized soil amended with cabbage residues. Phytopathology 83:899-905.

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