RECOVERY OF FIELD CORN FOLLOWING INSECTICIDE TREATMENT TO ARREST DEFOLIATION BY PSEUDALETIA-UNIPUNCTA (HAWORTH) (LEPIDOPTERA, NOCTUIDAE)

In Ohio, two sites of field corn, Zea mays L., severely defoliated by armyworm, Pseudaletia unipuncta (Haworth), were monitored to determine the level of armyworm injury from which corn would recover after inse cticide treatment to produce an economic grain crop. At both sites, th e predominant stage of corn plant development was the early to mid-who rl when treated, and average defoliation ranged from 40% to 97% depend ing on the plant development stage. Defoliation observed per leaf posi tion averaged 95% to 98% on the leaf closest to ground and declined as plant height increased. Post Rescue Treatment plant height was the pr imary indicator of potential plant recovery and subsequent yield. Wher e post-treatment plant height was arrested or reduced to within a rang e of 20 to 60 cm, a direct linear relationship existed between plant h eight and yield. Significant reduction in plant height occurred when d efoliation exceeded levels ranging from 60% to 80% depending on stand height that prevailed at the time of armyworm infestation. The results of this study were used to address the question of when a severely de foliated corn field should be salvaged by a rescue insecticide treatme nt or replanted to another crop.