The Control Effect and Toxicity of Fungicides on Tomato Seedling Damping-off Caused by Phytophthora capsici Leonian

In lab and greenhouse, the control effects of six fungicides on tomato seedlings damping-off caused by Phytophthora capsici Leonian and the impacts of fungicides to the growth of mycelium, the producing of sporangia, the releasing of zoospores of the pathogen were studied. As treated by soil-soaking, the control effects of hymexazol and isoprothiolane on the damping-off disease could reach 80% above, propamocarb and mancozeb could reach 60%~70%, and the effects of metalaxyl and iprodione only 50%. When treated with seed-soaking, the control effect of six tested fungicides was all lower than 60%. Metalaxyl had the highest toxicity to the growth of mycelium, the producing of sporangia, the releasing of zoospores of P. capsici, their EC50 values were 0.304, 0.742 and 2.725 mg/L. The toxicities of hymexazol and isoprothiolane on the producing of sporangia were also higher, and their EC50 were 0.875 and 2.888 mg/L, respectively, but their toxicities to the growth of mycelium and release of zoospores were lower than that of mancozeb. The next was mancozeb, which EC50 values to mycelium growth, sporangia producing and zoospores releasing of pathogen were 3.402, 10.243 and 23.561 mg/L respectively. The toxicities of propomocarb and iprodione were the lowest, their EC50 values were more than 100 mg/L.