Control of taro leaf blight using metalaxyl: effect of dose rate and application frequency.

Abstract

Metalaxyl (as Ridomil plus 72WP) was used to control leaf blight (Phytophthora colocasiae Racib.) of taro (Colocasia esculenta (L.) Schott) using a knapsack sprayer. A quadratic dosage-response curve is suggested. The technical optimum response occurs at 0.2 per cent Ridomil plus, using a fortnightly spray regimen. Five applications of 0.3 per cent Ridomil plus, at 3-weekly intervals during the middle of the growing period, can more than double the yield. The responses of yield to dose rate and application frequency are interpreted in terms of (1) the effect of Ridomil plus on the number of leaves per plant, (2) the proportion of plants exhibiting symptoms of blight, and (3) a phytotoxic effect.