Methods of application and rates of acephate for the control of Agrotis sp. (Lepidoptera: Noctuidae) in tobacco

Abstract

The efficiency of the insecticide acephate (O, S-dimethyl-N-acetyl phosphoramidothioate) was determined for the control of the cutworm Agrotis sp. in tobacco in the crop growing area of the state of Rio Grande do Sul, Brazil. The product was applied at rates of 500 and 1,000 g a.i./ha as strip spray on soil, as treatment of seedling roots by immersion in insecticide solution and as toxic baits. Sprayings on soil were made using a CO₂ hand sprayer with a Teejet nozzle delivering 142 ℓ /ha. The immersion treatment was done by placing the seedling roots in an insecticide solution before planting and the bait was applied using a manual Ortho Whirlybird Spreader. Except for the immersion treatment, the others were applied at planting and two weeks later. The trial was established in a randomized block design in a split plot scheme, with four replications. The field plots consisted of three rows of plants with ten seedlings per row transplanted in October/81. The effects of the treatments were evaluated by four weekly counts of the plants not damaged by the pest. The analysis of variance showed trio importance of Agrotis sp as a early season tobacco pest and showed that acephate at the dosages applied and using the application methods tested was efficient is, controlling the cutworm. After four weeks the stand reduction in the untreated check was 34.17% and in the acephate plots it was 13.33-18.49%. The use of toxic bait gave the best results due to the facility of application, selectivity to natural enemies and less risk of human and environmental contamination.