Field Management of Bruchids on Beans using selected Phytochemicals, Insecticides and Entomopathogen

Abstract

The effectiveness of selected synthetic insecticides, phytochemicals and an entomopathogen against pod sucker-, pod borer- and bruchid-damage on beans was determined in the field. Beans were sown at a spacing of 30 cm by 10 between and within rows in 2x4 m-sized plots. Nine treatments, including the controls were evaluated. Phytochemicals included crude extracts of Nicotiana tabacum, Phytolacca dodecandra, Tagetes minuta and Capsicum frutescens and were applied as unitary or cocktail formulations. Synthetic insecticides were Cypermethrin 5% EC and Fenitrothion 50% EC, while Beauveria bassiana was the entomopathogen. The controls were untreated beans. Application of the treatments commenced at pod filling stage, and a spray regime of once a week was maintained for five weeks. Damage due to pod suckers and pod borers were determined. Similarly, to determine the effect of the treatments on bruchid damage harvested beans were processed into 400-g working samples, and each was placed in 500-ml polystyrene bottles and incubated at ambiance until there was no more bruchid emergence in the laboratory. Bruchid load carry-overs from the field into storage were determined at 34 and 41 emerged adults during lsl and 2nd seasons, respectively. Efficacies of the different treatments varied significantly (P<0.05) in reducing pod sucker, pod borer and bruchid damage on beans. Untreated beans were the most damaged. Cypermethrin- treated beans were the least damaged and an 8-10 fold reduction in bruchid infestation was observed. Tobacco was the most effective botanical. The earliest and highest peak of bruchid emergence was in the untreated beans, unlike in the Cypermethrin- and tobacco-treated beans. A positive and significant relationship occurred between pod sucker and borer damage and A. obtectus infestation levels.