Management of major field insect pests and yield of cowpea (Vigna unguiculata (L) walp) under calendar and monitored application of synthetic chemicals in Asaba, southern Nigeria

The management of major field insect pests of cowpea under calendar and monitored sprays of cypermethrin was studied. The major 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. Influence of insect pest management on yield was also determined. The calendar sprays consisted of 7 days’ spray intervals carried out 5 times and 10 days’ spray intervals, carried out 4 times. Monitored spray was carried out only when insect pest infestation/damage reached or exceeded the action threshold. The experiments were conducted in the Teaching and Research Farms of the Agronomy department, Asaba Campus, Delta State University, Nigeria. Comparison of insect pests and grain yield from the calendar and monitored spray treatments was made if differences existed among them. Results indicated that all the cypermethrin treatments effectively controlled M. sjostedti, M. vitrata, flower bud thrip population and pod sucking bugs when compared to control in the early season. There was however, no significant difference (P>0.05) in calendar and monitored sprays. Similar observation was made for grain yield. In the late season, all treatments significantly (P<0.05) controlled pest population/damage on cowpea. Grain yield increase was similarly recorded but no differences among the treatments. Cowpea growers sometimes apply insecticides as many as 8 to 10 times to control insect pests during the growing season; the study here provides evidence (1) that 10 days' interval spray and monitored spray can be as profitable as 7 days’ interval spray in cowpea production and (2) this could reduce the number of chemical application, save cost as well as environmental pollution and hazards to consumers.