Seasonal and Genotypic Influence on Insect Pests, Growth and Yield of Cowpea (Vigna unguiculata L. Walp)

Cowpea (Vigna unguiculata L. Walp) is rich in dietary protein and a relish in most West African countries. Four elite genotypes (IT 97K-499-35, lT 97K-568-18, IT 98K-131- 2 and IT 93K-452-2) emanating from the breeding programme of International Institute of Tropical Agriculture (11TA), Ibadan were therefore evaluated for their relative adaptations to a rainy season environment. A local variety was added as a check. The accessions were laid out in a randomized complete block design (RCBD) in two seasons (early and late) for two years (2009 and 2010) at DEMACCO Integrated Farms Ltd., AKO, Enugu state, Nigeria. The result revealed the presence of genotype x season interaction. Reproductive grain yield and insect damage on the crop differed significantly (p<0.05) between genotypes and/or season. Pod weight, 100-seed weight, grain weight, threshing percentage and harvest index of the late crop increased by 31%, 25%, 72%, 71% and 41% respectively over that of the early. Late season grain yields of IT 93K-131-2 (1177.0 kg ha-I) and IT 93K-452-1 (1121.0kg ha-1) were outstanding compared to other genotypes and seasons and were more tolerant to pre-and post flowering insect pest. The early season grain yields of IT 93K-452-1 (1000.02 kg ha-1) and IT 97K-499-35 (987.00kg ha-1) were comparable to their respective late season yields (1121.00kg ha-1 and 898.22kg ha-1 respectively). Prevalence of pod sucking bugs and thrips were more evident on the late crops than on the early, while the reverse was the case for aphid, Maruca and Ootheca counts. Bruchid populations were not affected by seasonal variation.