Fungicidal control of anthracnose ( Microdochium panattonianum ) on lettuce

In field experiments in 1990 and 1991, 16 fungicides were evaluated for the control of anthracnose (Microdochium panattonianum) on lettuce. Prochloraz, chlorothalonil, and propiconazole were the most effective. No phytotoxic effects were observed in lettuce treated with either 0.23 g prochloraz/L or 1.15 g chlorothalonil/L, and both provided significantly better control than the recommended rates of mancozeb, propineb, and cupric hydroxide, widely used on lettuce in Australia. A mixture of prochloraz and chlorothalonil did not reduce the severity of anthracnose compared with either fungicide applied alone. Propiconazole at rates of 25 and 62.5 mg/L severely stunted plants, and this fungicide is not recommended for use on lettuce. Fungicides applied weekly were more effective than those applied on a 14-day schedule or those applied only after periods of leaf wetness. In most experiments unsprayed plants were severely diseased and weighed less than half of those treated with fungicides.