Control of the black bean aphid, aphis fabae scop. (homoptera aphididae) on french beans using neem-based pesticides in Kenya
The Black bean aphid, Aphisfabae Scopoli., is a major pest of beans in Africa. Due to its biology ( small size, feed on underside of the foliage, short generation time, short life cycle, high fecundity and resistance to pesticides), this pest is difficult to control, necessitating increased insecticide treatments which are uneconomical and ecologically undesirable. This study aimed at testing the efficacy of neem seed oil (NSO) as seed dressing, neem kernel cake powder (NKCP) as soil application, NKCP water extracts and neem oil EC, both as foliar sprays, in controlling the aphids. in addition, the effect of neem treatments on plant growth and yield were evaluated. Effective neem formulations were evaluated against Karate (Lamdacyhalothrin), a synthetic pyrethroid, and Gaucho (Imidacloprid), which belongs to the new chloronicotinyle insecticide group. Trials were done under screenhouse conditions at National Horticultural Research Center (NHRC), Kenya Agricultural Research Institute (KARl), Thika, Kenya. Neem seed oil (NSO- 0.8% Aza) at rates of 5, 10, and 15 mlsl Kg of seeds and 7g of NKCP (0.05% Aza) per planting hole had no significant effects on seed germination, plant growth and aphid populations (P = 0.05). However 14g and 28g of the NKCP had significant effect on the seed germination and plant growth (P = 0.05) but had no significant effect on aphid populations (P = 0.05). On the other hand, 25g, 50g NKCP water extracts, 2 and 3% neem oil EC (0.03% Aza) had no significant effects on plant growth but significantly affected aphid populations (P = 0.05). Neem oil EC and Karate were more effective than Gaucho which was similarly effective to NKCP water extracts. The yield of French beans was significantly higher in the insecticide treatments when compared to the control (P = 0.05) with Karate having the highest mean number of pods (10.3) and control had the least (3.3). Neem oil seed dressing and neem kernel cake powder soil application were found to be ineffective methods for aphidcontrol while NKCP water extracts and neem oil EC foliar applications controlled aphids aseffectively as the two synthetic chemicals. These findings may offer a novel aphid management and control programme by use of natural pesticides from the neem tree.