Evaluation of foliar insecticides for the control of western bean cutworm in field corn, 2021

The objectives of this field trial were to evaluate the efficacy of single applications of foliar insecticides at preventing feeding damage by the western bean cutworm (WBC), an important pest of corn and dry beans that has undergone a rapid range expansion into the eastern Corn Belt during the last 25 yr. This study was conducted within the historic range of WBC, at the University of Nebraska–Lincoln’s West Central Research, Extension, and Education Center in Lincoln County, NE (41.088374°N, −100.778969°W). A randomized complete block design with a total of 9 treatments (including an untreated check) and 4 replications was used. Plots measured 20 ft (8 rows) wide × 35 ft long. The trial was planted on 29 Apr 2021 using a commercial 8-row planter at 32,000 seeds/acre at an approximate depth of 1.40–1.75 inches in 30-inch rows. The seeds planted were NK0760-GT (Syngenta Seeds LLC, Greensboro, NC), a non-Bt hybrid with glyphosate herbicide tolerance. Irrigation, fertilization, and weed management inputs in plots followed standard agronomic practices for the region, with no insecticide applications other than the experimental treatments.

Plots were scouted weekly for the presence of WBC eggs and larvae following the onset of moth flight on 28 Jun. All foliar insecticide treatments were applied on 28 Jul using a backpack sprayer with an 8.3-ft handheld boom. Insecticides were delivered at 15-gpa carrier volume through 6 TeeJet AIXR 11002 air induction flat fan nozzles spaced 20 inches apart with 40 psi pressure maintained with a CO₂ propellant. Applications were made to a 10- × 30-ft area in the middle 4 rows of each plot with a single pass at 3 mph. At the time of treatment, 24% of plants were infested with an egg mass or larvae and 95% of plants had tasseled. On 25 Aug (28 days after application), 10 ears were randomly chosen and removed along with the husks from the central part of each plot. The ears were husked and examined in the laboratory to determine the amount of feeding damage, measured in square centimeters. The presence of lepidopteran larvae and secondary fungal infection in the ears was also recorded. On 4 Nov, a standardized subsample of ears (1/1,000 of an acre) from each plot was hand-harvested and shelled to calculate yield. Total grain weight and % moisture measurements were recorded and standardized to 56 lbs per bushel and 15.5% moisture. Ear feeding damage and yield data were analyzed using a mixed linear model with negative binomial distribution and log link function, with treatment as a fixed effect and block as a random effect (PROC MIXED, SAS v.9.4). For all analyses, mean separations were obtained using least square means with Tukey’s adjustment (α = 5%).

Approximately 14.72% of the total ears were infested with lepidopteran larvae, which were all identified as WBC. Secondary fungal infections were not found in any evaluated ears. The untreated check showed the highest feeding damage (11.06 cm²) and the highest rate of infested ears (62.5%) (Table 1). Elevest (6.7 oz/acre) performed best, with the lowest average damage per ear (0.56 cm²) and a low infestation rate (2.5%), followed by Besiege (7.2 oz/acre), Steward (8 oz/acre), Vantacor (1.2 oz/acre), and Intrepid Edge (8 oz/acre), which also significantly reducing damage compared to the untreated control (Table 1). Significant differences in yield were not observed.¹

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