Efficacy of Soil Fumigants and Compost On Soil Disease Management and Yield of Watermelon

The effect of supplemental compost on the efficacy of three soil fumigants in a polyethylene-mulched, drip-irrigated watermelon production system was examined. Well-aged dairy compost (0, 11.2, or 22.4 t∙ha^-1) was incorporated into the planting bed. InLine (1,3 dichloropropene + chloropicrin) was chemigated at 225 and 337 L∙ha^-1, Telone C-35 (1,3 dichloropropene + chloropicrin) was shank-applied at 337 L∙ha^-1, and K-PAM (potassium methyldithiocarbamate) was shank-applied at 505 L∙ha^-1, followed by 337 L∙ha^-1 chemigated. Soil Pythium, Fusarium and Verticillium dahliae populations were reduced by all fumigants, but K-PAM did not significantly reduce the V. dahliae population. Soil borne Pythium and Fusarium levels increased as compost application rate increased with InLine at 225 L∙ha^-1 and K-PAM. At the end of the season, soil Pythium levels were higher with C-35 as compared to the Check and Inline treatments, but Fusarium and V. dahliae levels were reduced. Compost rate did not influence soil borne plant pathogens at that time. Yield was not affected by either fumigation or compost application. The use of compost does not appear to provide a benefit in controlling these soil borne pathogens and may reduce the efficacy of some soil fumigants.