Efficacy of Fungicides for Control of Phytophthora Leaf Blight of Taro

Six fungicides were evaluated under greenhouse, laboratory, and dryland field conditions for control of Phytophthora leaf blight of taro incited by P. colocasiae. Five separate criteria were utilized to evaluate these fungicides: fungicidal activity in vitro; and fungicidal activity in vivo under conditions of simulated dew, simulated rainfall, greenhouse, and dryland field environments. In in vitro tests zoospores were killed at the following concentrations: Dithane M-45, 5 ppm; Difolatan, 9 ppm; Polyram, 65 ppm; Tribasic Copper Sulphate, 145 ppm; Benlate, 210 ppm; and Dyrene, 260 ppm. Excellent control was obtained with Difolatan; good control with Dithane M-45 and Polyram; and poor control with Benlate, Tribasic Copper Sulphate, and Dyrene. Results of in vivo tests correlated with those of the in vitro tests. Difolatan, Benlate, and Dyrene were the most phytotoxic while Tribasic Copper Sulphate, Polyram, and DithaneM-45 were the least phytotoxic.