California faces great challenges in sustainable strawberry production because the industry relies heavily on soil fumigants to control soil-borne pests, and more stringent regulations are being developed on fumigant use. Four field trials were used to investigate the potential of using low permeability tarp (e.g., virtually impermeable film or VIF, and totally impermeable film or TIF) to improve pest control efficiency and fumigant persistence and distribution in soil. Results from earlier field trials on VIF, which has a different structure than TIF, did not conclusively demonstrate improved weed control and strawberry yield than a standard tarp. The recent field trials using TIF indicate clearly that at the same application rate, TIF significantly increased fumigant concentrations under the tarp and in the soil thus resulting in much higher concentration-time exposure index values than for a standard tarp. The TIF further improved the uniformity of fumigant distribution in soil. All the data suggest that with TIF, reduced rates (e.g., half of the rate normally used with standard plastic tarp) can be used to achieve good efficacy. Furthermore, the increase in the application rate of fumigants slowed down the degradation rate more significantly on chloropicrin compared to 1,3-dichloropropene. Thus, using a reduced rate under TIF is also necessary because of the increased fumigant persistency in soil in order to prevent a surge of emissions during tarp-cutting to protect workers and bystanders, and to avoid extended tarp cover duration that may affect planting time. This research has contributed to providing a long term solution for sustainable strawberry production through the use of low permeability tarp in soil fumigation that can result in less chemical input, higher fumigant efficiency, and more environmentally sound practices.
