Effect of Metalaxyl, an Acylalanine Fungicide, on Developmental Stages ofPhytophthora infestans

Abstract

A systemic acylalanine fungicide (metalaxyl) effectively inhibited growth and development of P. infestans in potato [Solanum tuberosum] foliage. The fungicide, at low concentrations, inhibited lesion appearance, expansion and sporulation from lesions, and reduced the germination of sporangia produced from lesions on treated leaves. When leaves were treated before inoculation with low concentrations of metalaxyl (10 .mu.g a.i.[active ingredient]/ml), lesion appearance was suppressed. The number of sporangia produced from lesions and their subsequent germination was dramatically suppressed by low concentrations of metalaxyl (10-30 .mu.g [a.i.]/ml) when applied after inoculation, and by slightly higher concenrations when applied before inoculation. Soil applications also effectively suppressed the development of P. infestans. The fungicide at low concentrations (25 .mu.g[a.i.]/ml) suppressed in vitro sporangium germination of 1 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.