Survey of chocolate spot (Botrytis fabae) disease of faba bean (Vicia faba L.) and assessment of factors influencing disease epidemics in northern Ethiopia

Field surveys were conducted in northern Ethiopia during the 2004 and 2005 cropping seasons to determine the distribution of chocolate spot (Botrytis fabae) and the association of disease parameters (incidence and severity) with crop management practices. A total of 261 faba bean fields were surveyed in 12 districts and chocolate spot affected all fields. Disease incidence and severity varied among districts and cropping seasons. Significant differences among locations were observed due to altitude, plant density, date of planting, crop growth stage and field management practices. Mean disease incidence of chocolate spot varied from 47 to 100% in most fields while disease severity index ranged from 17 to 49%. The correlation between disease parameters and altitude, field size, plant population and weed density was positive with disease incidence (r = 0.565) and severity (r = 0.521). Chi-squared analyses of disease incidence and severity revealed a higher frequency (P < 0.001) of diseased fields in western than in eastern districts of the northern region. This finding was supported by the high power of prediction (R2) that was found for the association between districts and the incidence (46%) and severity (45.1%) of chocolate spot disease. High precipitation, high weed density, and early planting also made significant contributions (P < 0.01) to chocolate spot epidemics in farmer fields. Western districts of northern Ethiopia, which are more favourable for the development of chocolate spot disease epidemics should be especially targeted for integrated disease management. Our findings indicate that proper weed management and manipulation of planting date are interventions that can reduce the impact of chocolate spot disease in Ethiopia.