Department of Plant Pathology, College of Agriculture Andhra Pradesh Agricultural University, Hyderabad-500030.
For fixing up the threshold level for powdery mildew (Erysiphe polygoni) in cluster-bean (Cyamopsis tetragonaloba var. Pusa-Nav-Bahar), a field trial was conducted for two crop seasons. at Hyderabad. The linear regression equation derived suggests that no loss in yield occurs upto 26 per cent disease incidence (Pill) thereby indicating this to be the threshold level. Seed dressing with ethirimol and foliar spray with wettable sulphur resulted in the lowest PDI and highest yield. Therefore, except seed-dressing, the foliar spray can be delayed until the PDI value reaches 26 or altogether avoided if it does not reach that level. Thus, the investment on foliar spray of fungicides can be minimised.
