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Effect of Protectant Fungicides on the Developmental Stages of Phytophthora infestans in Potato Foliage. R. I. Bruck, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address: Department of Plant Pathology, North Carolina State University, Raleigh 27650; W. E. Fry(2), A. E. Apple(3), and C. C. Mundt(4). (2)(3)(4)Department of Plant Pathology, Cornell University, Ithaca, NY 14853, (4)Present address: Department of Plant Pathology, Iowa State University, Ames 50010. Phytopathology 71:164-166. Accepted for publication 26 June 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-164.

Two protectant fungicides, mancozeb and chlorothalonil, inhibited the development of in vitro and in vivo Phytophthora infestans. Germination of zoospores or sporangia was inhibited by low concentrations of either fungicide. Following fungicide application on infected leaves, lesion expansion and fungal sporulation were suppressed. The timing of fungicide application in relation to the stage of late blight development had a significant influence on fungicide efficacy. The most important effects of these fungicides were inhibition of spore germination and suppression of the viability of sporangia produced from treated foliage.