Detection of Antifungal Activity in Potato Tubers Field-Treated with Metalaxyl, a Systemic Fungicide. S. K. Bhatia, Research Technologist, Division of Plant and Soil Sciences, West Virginia University, Morgantown 26506. R. J. Young, Professor, Division of Plant and Soil Sciences, West Virginia University, Morgantown 26506. Plant Dis. 67:1075-1079. Accepted for publication 1 April 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1075.

The systemic fungicide metalaxyl (Ridomil), when applied to soil or foliage, effectively controlled potato late blight. Tubers of the cultivar Katahdin were harvested from plants treated with metalaxyl and/or conventional fungicides and tested for antifungal activity. No evidence of fungal inhibition was observed in tubers sampled from plants treated with standard fungicides, but tubers sampled from some metalaxyl-treated plants showed completely inhibited growth and development of Phytophthora infestans, indicating an antifungal substance was present. Additional experiments confirmed that the antifungal property was uniformly distributed to all areas of the tuber, and the effect persisted beyond 110 days in storage both at 5 and 20 C. Tubers 10 cm in diameter and larger were more resistant to infection than smaller tubers. When metalaxyl was applied at 0.414 kg/ha or less, no antifungal activity was detected by this bioassay. Higher rates of metalaxyl (1.7 kg/ha) caused tubers to break dormancy earlier; sprouts developed sooner and more abundantly.