Effect of Farming Practices, Crop Stage and Season on Black Bean Aphid Infestation on Common Beans in Western Kenya

Abstract

Beans (Phaseolus vulgaris, L) are among the most important food legume crop in Kenya. However, damage by black bean aphid (Aphis fabae, Scopoli) has greatly reduced bean yields. This study was undertaken with a general objective of determining the effect of farmer practices, crop stage and season on A. fabae incidence and severity on common beans (P. vulgaris) in western Kenya. Two surveys were carried out during the short rain (SR) and long rain (LR) seasons of 2013 in six agro-ecological zones (AEZs): LM_1, LM₂, LM₃, LM_4, UM₁ and LH₁.Purposive and random sampling methods were used to select fields of participating and non participating farmers in legume improvement project. Ten plants were randomly selected and sampled for aphid infestation in each field. Analysis of variance was used to compare means of aphid incidence and severity under different treatments. LSD was used to separate means at P< 0.05 level of probability. During the short rains, the highest incidence of 48.6% and severity scale rating of 1.83 was recorded on vegetative stage. Lowest aphid incidence of 4.89% and severity scale rating of 1.06 was observed on mature stage of the crop in the long rain season. Highest incidence of 26% and severity scale rating of 2.12 was recorded on fields applied with DAP during the SR while the lowest incidence of 9.48% and severity rating of 0.67 was recorded when no fertilizer was used in the LR. A higher aphid incidence of 22% was noted on fields of NP farmers during the SR compared to incidence of 10.78% on plots of P farmers during the long rains. Generally higher aphid incidence under different treatments was recorded during the SR season as compared to the LR season. These findings will help the farmers to plant common beans using farming practices and during seasons that could lower aphid infestations. This is expected to lower costs associated with aphid control and guarantee farmers higher yields.