Pest Status of Black Bean Aphid on Common Beansin Agro-Ecological Zones of Western Kenya
Aphis fabae, Scopoli, is one of the important pests of beans and causes significant yield losses in Kenya. The objective of this study was to determine A. fabae incidence/severity on common bean (P. vulgaris) varieties in pure stand and bean/maize intercrop in Agro-ecological zones (AEZs) of western Kenya. Two surveys were done during the short and long (2013) rain seasons in six AEZs: LM1, LM2, LM3, LM4, UM1 and LH1.Purposive and random sampling method in which participating and non participating farmers in legume improvement project were interviewed. Ten plants were randomly selected and sampled in each field. Analysis of Variance was used to determine mean aphid incidence/severity in various AEZs, Altitudes, among bean varieties and between pure stand and bean/maize intercrop. LSD was used to separate means at P<0.05 level of probability. Highest incidence (36.2%) and severity rating (1.6) respectively was recorded in LH1 in the short rains. In this period, lowest incidence of 0.7% and severity rating of 1.0 was in LM4.Highest incidence of 35.1% was during the short rains in altitude range of 1601-2000 m.a.s.l and the lowest (1.1%) in the same season in altitude 0-1200 m.a.s.l. Short rains recorded the highest severity scale rating of 1.6 in the altitudes 1201-1600 and 1601-2000 m.a.s.l. Lowest severity rating in both long and short rain seasons was 1.0 in the altitude 0-1200 m.a.s.l. Variety KK8 recorded the highest incidence and severity of 47.1% and 1.77 respectively in the short rains. On the contrary varieties Wairimu and GLP 1127 in the short rains and varieties Punda and Zaire in the long rains were not infested. There was significant difference in aphid infestation on beans between bean pure stand and bean/maize intercrop in the short rains. Higher incidence (31.3%) was in pure stand compared to 11.9% in bean intercrop. Similarly severity rating of 1.5 and 1.2 was recorded on pure stand and intercrop respectively. Findings of study will assist farmers in selecting varieties to plant in bean pure stand or bean/maize intercrop in the AEZs of Western Kenya.
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