Abstract A large-plot field study was conducted on a commercial farm near Kingsville, TX to evaluate the effectiveness of Dipel for control of Heliothis zea. Dipel and an untreated were compared in 100-row by 1400-ft plots of cotton planted 6 Mar on 38-inch rows. Entries were replicated 3 times in a paired block design. Dipel was applied beginning at the first-bloom-stage on 16 and 23 May. Both applications were made with an airplane calibrated to deliver 4 gal total spray/acre. Efficacy of Dipel was evaluated by inspecting 50 squares and 50 bolls in each plot for the presence of Heliothis zea damage. Seed cotton for yield analysis was hand-harvested from designated 13.5-ft sections of row in each plot.