EFFECTS OF SOIL FUMIGATION WITH METHYL-BROMIDE AND CHLOROPICRIN ON ROOT HEALTH AND YIELD OF STRAWBERRY

Soil fumigation with methyl bromide and chloropicrin (MBC) reduced the severity of black root rot of strawberry in experiments at four locations in California. At three of these sites, fumigation increased root density by 19-61% over the untreated controls. Improvement of root health by fumigation was correlated with increased yields of berries at all four locations. Accumulative harvests from fumigated plots were 24-29% greater than the untreated controls. At a fifth location, fumigation with MBC had no significant effect on root growth, root rot severity, or yields, and this may have been partly attributable to low disease levels. In comparison to MBC, preplant soil applications of metham-sodium and metalaxyl had no effect on root disease levels, root development, or yield. Commercial strawberry cultivars compared in experiments at two locations responded similarly to soil fumigation with MBC. Black root rot was the only disease of significance in all locations; Cylindrocarpon destructans, Pythium ultimum, and P. irregulare were the fungi isolated most often from diseased plants.