Influence of cowpea genotype and sorghum-cropping system on cowpea infestation by some insect pests in the sudan savannah of Nigeria

Abstract

Field trials were conducted at the International Institute of Tropical Agriculture, Agricultural Research Station at Minjibir, Kano State (12013’N, 8041’E, 500M above sea level) in the 1999 and 2000 cropping seasons to investigate the influence of cowpea genotypes and sorghum cropping system on cowpea damage by legume pod borer, Maruca testulalis (Fabricius), bean flower thrips, Megalurthrips sjostedti (Trybom) and cowpea aphids, Aphis craccivora Koch. Treatments consisted of a combination of 6 cowpea genotypes, namely, Danila, IT90K-277-2, IT95K-1091-3, IT95K-222- 14, IT96D666 and IT96D-759 and 4 row arrangements, which included 1M:1C, 2M:2C, 1M:2C and 2M:4C rows of millet to rows of cowpea, respectively. The treatments were laid out in split plot design with row arrangement and cowpea genotype as main and sub-treatments, respectively. Maruca damage ratings on cowpea were recorded based on damage to flowers and pod on the peduncles using 1-9 scale. For aphids, level of infestation was assessed by estimating number of aphid colonies on plants/plots at flowering stage using 0-9 scale, while for thrips, infestation was estimated at post-flowering stage using a scale of 1-9. Result showed that all treatments, except Danila and IT96D-759 were less susceptible to pod damage by Maruca in both 1999 and 2000. Maruca pod damage was significantly higher in 2S:4C row arrangement compared to other treatments. Significantly lower aphids and thrips population were recorded on all treatments except Danila and IT6D-759 and Danila and IT95K-1091-3 in both 1999 and 2000, respectively. The mean number of aphids was lower in 1S:1C in 2000 (2.14) and thrips infestation was highest at 2S:4C row arrangement in 1999 and 2000, respectively. The total dry matter and grain yield increased progressively from 1S:1C through 4S:4C in both 1999 and 2000. The present study suggests that sorghum-cowpea inter crop and the use of improved cowpea varieties should be adopted as control measures against the devastating effects of Maruca, aphids and thrips, thereby improving the cowpea dry matter and grain yield.