Inoculum sources and management of bean scab caused by Elsinoë phaseoli

Abstract

Bean scab caused by Elsinoë phaseoli is a major challenge to common bean cultivationin Kenya. However, knowledge about its epidemiology and management is limited.This study conducted three experiments in Kakamega, Kenya, evaluating scab inocu-lum sources and control options. The first experiment evaluated three different inoc-ulum sources over two seasons; bean crop residue caused the highest scab incidencein both the 2021 (62.1%) and 2022 (81.1%) seasons. The second experiment assessedthe effect of rotation history on scab over three seasons. Scab incidence consist-ently surpassed 90% within the first 30 days after planting in half-yearly rotated fieldsacross all seasons, while the disease was absent after planting in fields with no recenthistory of legumes. Fields rotated out of legumes consistently had the highest grainyield, averaging 1.5 t ha−1 over the seasons. Additionally, the rotation land treatmentdisplayed significantly more pods per plant during the 2021 (9.7), 2022a (9.8), and2022b (12.5) seasons. In the third experiment, the impact of five fungicides and fourcropping systems on bean scab was investigated over two seasons. Neither fungicidetreatments nor cropping systems had an effect on bean scab incidence even whenonly severe symptoms were considered. Carbendazim had the highest yield (1.9 t ha−1)outperforming the unsprayed control only in the 2022 season while none of the otherfungicides outperformed the control treatment in yield parameters in either season.This study emphasizes the challenge of managing bean scab without proper crop rota-tion and underscores the role of crop residue as a critical inoculum source.