Evaluation of Acibenzolar-S-Methyl and Silicic Acid for control of Phytophthora Blight Caused by Phytophthora capsiciin Squash
Phytophthora blight caused by Phytophthora capsici Leonian is a destructive disease of squash (Cucurbita pepoL.) in Florida and worldwide. Greenhouse studies were conducted to evaluate the potential of acibenzolar-S-methyl and silicic acid for control of Phytophthora blight in squash. Applied as a soil drench or foliar spray, acibenzolar-S-methyl alone at 20 and 30 mg·L–1 significantly (P< 0.05) reduced disease severity compared to the nontreated control. AcibenzolarS-methyl applied as a soil drench at 30 mg·L–1 provided the greatest protection with no symptoms developed on treated squash plants. Silicic acid applied as a soil drench at 0.015 and 0.15 mM significantly suppressed disease severity by 47.7% and 53.3%, respectively, and increased Si concentration in squash roots by 36.2% and 44.4%, respectively, when compared with the nontreated control. Soil application of silicic acid in combination with acibenzolar-S-methyl improved the efficacy of silicic acid and acibenzolar-S-methyl each applied separately against Phytophthora blight. In vitro testing indicated that neither silicic acid nor acibenzolar-S-methyl at test rates suppressed P. capsiciby inhibiting growth of mycelia, production of sporangia or germination of zoospores. Results in this study suggest that acibenzolar-Smethyl and silicic acid were effective against P. capsiciin squash and may be incorporated into integrated management programs for control of Phytophthora blight in squash.