Evaluation of neem seed extract for the control of major field pests of cowpea (Vigna unguiculata L. Walp) under calendar and monitored sprays

Abstract

Cowpea growers sometimes apply chemicals as many as 8-10 times to control insect pests during the growing season. Calendar sprays at 7 days' intervals (CA.S7) carried out 5 times and 10 days' intervals (CA.S10) carried out 4 times and monitored spray (MOS) carried out only when insect infestation/damage reached or exceeded the action threshold were studied to find out their effect on major insect pests and yield of cowpea - whether there were differences in the number of insect pests and grain yield. The insect pests studied were the cowpea aphid, Aphis craccivora Koch, legume bud thrips Megalurothrips sjostedti Tryb, legume pod borer, Maruca vitrata Fab. and pod sucking bugs under the application of 5% aqueous extract of neem seed kernel extract (NSKE). The trials were conducted during the early and late planting seasons in Abraka, on a piece of land half a kilometre to Campus 2, Delta State University, Nigeria. The results indicated that calendar sprays significantly controlled A. craccivora colonies compared to control in the early season. Population of other major insect pests was generally low. During the late season, the various NSKE treatments effectively controlled A. craccivora. No significant difference among the treatments in their effect on the other major insect pests. Grain yields were high in both seasons and a significant difference did not exist among the calendar and monitored spray treatments. Three main things are obvious from this study: (1) neem seed kernel extract is effective in the control of cowpea insect pests, especially A. craccivora, (2) Grain yields were similar in calendar and monitor sprays. (3) spraying every 10 days for 4 times and monitoring insect pest damage/infestation before spraying reduced the number of chemical application.

Keywords: Cowpea, insect pests, neem extract, calendar and monitored sprays.