Evaluation of Selected Insecticides for Control of Corn Earworm in Grain Sorghum, 2016*

Corn earworm is the primary caterpillar pest of grain sorghum in Tennessee and can cause substantial yield reductions. Larvae are direct pests that feed on the developing and mature kernels in sorghum heads. Selected insecticide treatments were evaluated for control of corn earworm in grain sorghum at the West Tennessee Research and Education Center at Jackson, TN. Grain sorghum was planted on 8 Jun. The test was arranged in a RCB design with four replicates. Individual plots were 12.67×35 ft. Treatments were applied with a high clearance sprayer calibrated to deliver 9.1 GPA at 40 PSI with 8001 flat fan nozzles. Foliar application was made 9 Aug. Insect control was evaluated 15 Aug, 6 days after treatment (6 DAT) and 18 Aug (9 DAT). Plots were sampled by bending and vigorously shaking a fixed number of sorghum heads from the center two rows of each plot into a standard 15-inch sweep net and counting larvae in the net dislodged from the heads. More sorghum heads were sampled at the later evaluation timing in order to collect sufficient numbers of larvae for statistical separation among treatments. Yield data were collected 30 Sep by harvesting two center rows of each plot with a plot combine. Data were subjected to ANOVA and means were separated using a LSD test.

All insecticide treatments significantly reduced the numbers of total corn earworm larvae found at both evaluation timings (Table 1). On either rating date, treatments including Prevathon or Blackhawk provided statistically similar control. Karate Z had significantly more small corn earworm than the other insecticide treatments at 6 DAT, and larval numbers were not different than the untreated check. Prevathon alone or with fungicide had fewer large corn earworm than did Karate Z at 6 DAT. All insecticides reduced the number of large corn earworm at 9 DAT. Prevathon applied alone had fewer large corn earworm compared with Karate Z. All insecticide treatments yielded more than the untreated check. Plots treated with Karate Z yielded significantly less than the other insecticide treatments. No phytotoxicity was observed with any treatment.

Author notes

Subject Editor: Jawwad Qureshi