In Vitro Fungicidal Activity of Calcium and Potassium Salts on Several Commercially Significant Plant Pathogens

In vitro dose responses of several calcium and potassium salts were determined on some commercially significant plant pathogens, including: Helminthosporium solani , Fusarium oxysporum f. sp. pisi race 2, Colletotricum coccodes , Phytophthora cactorum , Phytophthora cinnamomi , Phytophthora erythroseptica , Phytophthora infestans , Phytophthora megasperma , Pythium ultimum , and Venturia inaequalis . Mycelial growth inhibition was both salt-specific and dose-related. Pythium ultimum was completely inhibited by 75 mg·L −1 or greater calcium propionate, but needed 300 mg·L −1 or greater of calcium acetate and 40 mL·L −1 or greater of potassium silicate for complete inhibition. Phytophthora infestans was completely inhibited by 150 mg·L −1 or greater calcium acetate, 150 mg·L −1 or greater calcium propionate, or 5 mL·L −1 or greater potassium silicate. Phytophthora cactorum was completely inhibited by 300 mg·L −1 or greater calcium propionate, but required 600 mg·L −1 or greater calcium acetate and 10 mL·L −1 or greater potassium silicate for complete inhibition. Phytophthora cinnamomi was completely inhibited by calcium propionate at 600 mg·L −1 or greater or by 10 mL·L −1 or greater potassium silicate. Only potassium silicate inhibited Phytophthora megasperma , Phytophthora erthroseptica , V. inequalis , and H. solani at concentrations of 5 mL·L −1 or greater, 20 mL·L −1 or greater, 40 mL·L −1 or greater, or 80 mL·L −1 or greater, respectively. Potassium acetate did not completely inhibit any of the pathogens in this study when tested at concentrations 1200 mg·L −1 or less.