Efficacy of Insecticides Against Tobacco Budworm and Bollworm in Late Season with Post Optimal Appli-Cation Timing, 1991

Cotton was planted 1 Jul with plots consisting of 4 rows (102 cm centers) x 9.1 m. Treatments were arranged in a RCB design, replicated 4 times. Applications were made with a tractor mounted boom equipped with a compressed air system calibrated to deliver 56.2 liters total spray/ ha through Teejet X-8 hollow cone nozzles (2/row) at 2.39 kg/cm2. Insecticide treatments were applied on 10 and 16 Sep. Methyl parathion 4 EC (0.37 kg [AI]/ha) was applied on an “as needed” basis for boll weevil control. Efficacy was determined by examining 25 squares/plot for evidence of damage and the presence of larvae. High numbers of soybean looper larvae were observed in the plots during Sep and visual defoliation estimates were made to evaluate differences among treatments. Each plot was scored as follows: 0 (no feeding damage), 1 (feeding damage within the lower 1/3 of the plant), 2 (feeding damage to the lower and middle 1/3 of the plant) or 3 (feeding damage throughout the plant). No rainfall occurred during this test. Sprinkler irrigation was provided “as needed” during the test but not within 48 h following treatment applications. Insecticide applications were delayed until infestations of bollworm and tobacco budworm larvae in varying stages had become established in the plots.