Association of bean rust and common bacterial blight epidemics with cropping systems in Hararghe highlands, eastern Ethiopia

Surveys of common bean rust and common bacterial blight (CBB) diseases were conducted in the Habro, Chercher and Wobera. areas of the Hararghe highlands, Ethiopia during the 1998 and 1999 cropping seasons in four different bean cropping systems, Intercropping constituted 91% of the cropping systems. Bean proportions in intercropping ranged from 13 to 55%. In intercropping, the mean rust incidence and severity was reduced by 25 and 16%, respectively, compared with sole cropping. Similarly CBB incidence was reduced by 29% while severity was reduced by 20%. Single and multiple variable logistic regression analyses were used to determine the association of rust and CBB diseases with cropping systems and practices, geographical areas, cropping years and altitude. The analyses indicated that cropping system, geographical area and cropping year were important variables and affected both rust incidence and severity. In Habro during 1998 there was a high probability of rust incidence and severity greater than 25%. The probability of rust incidence and severity exceeding 25% in Habro was about 11 and 4 times greater than in Chercher and Wobera areas, respectively. Less than 50% bean proportions in intercropping were significantly associated with low (< 25%) rust severity, Similarly geographical area, altitude and cropping system affected CBB incidence and severity. In Habro and at lower altitudes there was a high probability of greater than 25% CBB incidence and severity. Bean plants at podding and or maturity were closely associated with high rust and CBB severity. Intercropping systems were more associated with lower CBB and rust intensity than sole cropping.