Effects of Metalaxyl on Phytophthora cinnamomi Root Rot of Abies fraseri. Robert I. Bruck, Assistant Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Charles M. Kenerley, Graduate Student, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Plant Dis. 67:688-690. Accepted for publication 2 December 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-688.

Greenhouse and field experiments were initiated in 1980 to determine the efficacy of metalaxyl (Subdue 2E and 15G) as a control for Phytophthora root rot. Two-year-old greenhouse-grown fir trees were protected from P. cinnamomi when treated with metalaxyl either before, during, or up to 7 days after soil infestation with fungal propagules. Three-year-old greenhouse-grown seedlings treated with the highest metalaxyl rate (250 μg a.i./ml) as late as 15 days after soil infestation remained asymptomatic and attempts to recover P. cinnamomi from their roots were unsuccessful. Survival of P. cinnamomi propagules living free in the soil was completely retarded only at a high fungicide rate (250 μg a.i./ml) 7 days posttreatment; however, after 48 days, no propagules were detected at rates > 1.0 μg a.i./ml. In nursery bed trials, Fraser fir seedlings were protected from root rot and spread of the fungus within nursery beds was arrested. Metalaxyl may be effectively employed as a prophylactic root rot fungicide against Phytophthora root rot of Fraser fir.