Efficacy of Selected Insecticides for Control of Fall Armyworm in Bermudagrass Hay, 2014 *

The fall armyworm is an annual pest of Bermudagrass grown for pasture and hay in northeast Texas. The objective of this study was to compare the efficacy of three insecticides for control of FAW in common Bermudagrass grown for hay. The study was conducted in late September in a field of common Bermudagrass at the Texas A&M Research and Extension Center near Overton, TX. An RCB design was used to assign four replications of each of four insecticide treatments and an untreated check to plots each 30 ft × 50 in size. Insecticides were applied with a compressed CO ₂ backpack sprayer equipped with XR TeeJet extended range flat spray tips and calibrated to deliver 10 gallons/acre at 20 psi. A non-ionic surfactant (Spreader 90) at ¼% was added to each insecticide. Treatments were applied once on 24 Sept 2014. FAW larvae populations were assessed by taking four to eight sweeps per plot using a standard 15-in. sweep net. FAW densities were sampled one day prior to application and on 25, 28 Sept and 1, 8 Oct (1, 4, 7, and 14 DAT). The number of FAW larvae per treatment and date were analyzed using ANOVA and means were separated by Fisher’s-protected LSD ( P  < 0.05). Percent control was calculated using the Henderson-Tilton formula. The percent values were transformed by arc sine square root transformation, subjected to ANOVA and means were separated by Fisher’s-protected LSD ( P  < 0.05). Belt SC was not registered for use on hay at the time of application and therefore the treated forage was destroyed at the end of the trial.

The mean length of a sample of larvae ( n  = 53) collected 25 Sept from the untreated plots was 0.45 in. (range 0.38–1.0 in.). FAW densities were not different among treatments one day prior to insecticide applications. One day after treatment, FAW densities were significantly less in all treatments except the Intrepid treatment. Intrepid is an insect growth regulator and the delay in larval mortality is expected at 1 DAT. At 4 DAT, FAW densities were significantly lower than the untreated in all treatments except the 2.0 oz rate of Belt SC. The percent control ranged from 60 to 93% and treatments did not differ. At 7 DAT, FAW densities in all treatments were significantly less than in the untreated and percent control was 96–99%. No FAW were recovered from any of the treatments or untreated at 14 DAT.

Author notes