The roles of three fungicides in the epidemiology of potato late blight

Three fungicides were tested in the field for efficacy on late blight cause d by Phytophthora infestans. The effects of these fungicides on epidemic de velopment, lesion growth rate and sporulation were measured. No fungicide c ompletely arrested epidemic development under the environmental conditions of these experiments. However, the fungicide mixture, propamocarb hydrochlo ride plus chlorothalonil, had the most suppressive effect of the fungicides tested. The mechanism of effect included suppression of disease progress a nd lesion expansion. Growth chamber studies demonstrated that 24 degreesC c ompared to 10 or 16 degreesC limited cymoxanil efficacy.