Assessment of Crop Loss due to Soybean Rust Pathogen

Soybean rust caused by Phakopsora pachyrhizi (Syd.) Butler and Bisby occurs regularly and severely in restricted areas of Northern Karnataka causing yield loss upto 20–80 per cent. Therefore, estimation of crop loss is an important factor in determining the economic importance of the disease and to develop cost effective control measure. In this context, loss estimation trial on soybean rust was conducted in an endemic area (Ugarkhurd) during Kharif 1999 and 2000. Lower disease index (16.8 to 13.8) and (16.6 to 13.0) with increase in seed yield (78.2 - 75.9% and 81–85% was obtained in plots receiving three to six sprays of hexaconazole (0.1%) on a susceptible cv. JS-335 and two to six sprays of the same in moderately resistant cv. PK-1029, respectively. Maximum benefits and higher yield were obtained from the plots receiving three and two spray of hexaconazole in JS-335 (1:5.2) and PK-1029 (1:6.3), respectively. Therefore, the results of two years of field studies prove that in a susceptible cv. JS-335, three sprays of hexaconazole are sufficient to manage the rust and realise the higher economic yields while on moderately resistant cv. PK-1029, two sprays are enough to lower the disease severity and to obtain higher yields.