Web blight of common bean-epidemiology and fungicide application

Abstract

The progress of web blight (Thanatephorus cucumeris) epidemic in common beans (Phaseolus vulgaris L.), in relation to number and timing of different fungicidal sprays was studied in three field experiments conducted in Transamazon region. The disease increased at the rate of 0.29 unit per day in untreated plots under favorable conditions. The systemic fungicides benomyl and oxycarboxin were more efficient in reducing she infection rate than protectants such as mancozeb and copper oxychloride. Increase in number of sprays with systemic fungicides proportionately delayed the onset of epidemic. Early sprays in the vegetative growth stage of bean crop were more effective in slowing the rate and delay the disease onset. The results further showed that the leaf lesion size increased in accordance with the exponential law.