A Field Cage Study to Evaluate the Efficacy of Selected Insecticides Against Beet Armyworm on Transgenic Bt Cotton, 1997

Transgenic cotton, expressing the crylA(c) gene (Bollgard Gene, Monsanto Co., St. Louis, MO) from Bacillus thuringiensis ssp. kurstaki and non-transgenic cotton were planted 17 Apr in Corpus Christi, Texas. Plots consisted of 4 rows X 30 ft. Treatments were arranged in a RCBD with 5 replications. A 6-inch band of insecticide, Temik 15 G (0.7 lb [AI]/acre), was applied at the time of planting and all plots were oversprayed with insecticides as needed for control of non-lepidopteran pests such as cotton fleahoppers, aphids, and boll weevils. Beneficial insects were eliminated by overspraying the entire test with pyrenone on 14 Jun, 2 d prior to infesting cages with beet armyworms. Tracer (0.045 lb [AI]/acre) and Pirate (0.09 lb [AI]/acre) were applied on the appropriate plots on 16 (replicates 1, 2, and 3) and 17 Jun (replicates 4 and 5) using a backpack CO2-powered sprayer with a 2-row hand-held spray boom. Plants were caged and infested within 4 h following the spray applications of Pirate and Tracer. In each plot, two nylon organdy cages were placed over blooming cotton plants, 3 adjacent plants per cage. Then the plants in each cage were uniformly infested with 50 beet armyworm neonates. Natural infestations of bollworm, tobacco budworm, fall armyworm, and cabbage looper were also present. Cages containing the cotton plants were removed lid after infestation and taken to the laboratory for evaluation. Data collected per cage were number of larvae, larval weight, number of injured terminals, flower buds and bolls, and an overall rating of leaf injury. The leaf injury was visually rated using the following scale: 0≤5%; 1=6-25%; 2 = 26-50%; 3>50% of leaves injured. All data, except larval weight and leaf injury rating were transformed ln(x + 1) prior to statistical analysis. Untransformed means are presented here.