VIEW ARTICLE

Disease Control and Pest Management

Effect of Metalaxyl, an Acylalanine Fungicide, on Developmental Stages of Phytophthora infestans. R. I. Bruck, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27650; W. E. Fry(2), and A. E. Apple(3). (2)(3)Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 70:597-601. Accepted for publication 10 December 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-597.

A systemic acylalanine fungicide (metalaxyl) effectively inhibited growth and development of Phytophthora infestans in potato foliage. The fungicide, at low concentrations, inhibited lesion appearance, expansion and sporulation from lesions, and reduced the germinance of sporangia produced from lesions on treated leaves. When leaves were treated before inoculation with low concentrations of metalaxyl (10 μg [a.i.]/ml), lesion appearance was suppressed. The number of sporangia produced from lesions and their subsequent germinance was dramatically suppressed by low concentrations of metalaxyl (10–30 μg [a.i]/ml) when applied after inoculation, and by slightly higher concentrations when applied before inoculation. Soil applications also effectively suppressed the development of P. infestans. The fungicide at low concentrations (25 μg[a.i.]/ml) suppressed in vitro sporangium germination of one isolate (race 1, 2, 4) but not of another isolate (race 1, 2, 3, 4). These data help explain how this fungicide effectively suppresses established epidemics of potato late blight.