Lepidopteran Pest Control in Sweet Corn With Insecticides Allowed for Organic Production, 2019

The objective of this study was to evaluate the efficacy of insecticides allowed for organic production to control Lepidopteran pests, especially corn earworm (CEW), on sweet corn. Sweet corn ‘Generator F1’ was direct seeded on 9 Jul 2019 at Cornell AgriTech’s Fruit and Vegetable Research farm in Geneva, NY (GPS: 42°52′24.8″N 77°01′46.4″W). Seeds were planted 8 inches apart within rows, and rows were spaced 30 inches apart. Each plot consisted of two 30-ft-long rows and was flanked by two unplanted rows. Plots also were separated from each other within rows by 8 ft of bare ground. Five replications of each treatment were arranged in an RCB design. Insecticides and application rates are provided in Table 1. Insecticides were applied using a CO₂-pressurized backpack sprayer and boom equipped with two flat-fan nozzles (XR-Teejet 8002) calibrated to deliver 28 gallons per acre at 40 psi. Nozzles were separated by 20 inches and directed horizontally toward the primary ear and applied to only one row at a time. All treatments were co-applied with the OMRI-listed surfactant, Nu Film P, at a rate of 8 fl oz/acre. Insecticide applications were initiated on 7 September, shortly after most ears had produced green silks, and additional applications were made on 10, 13, and 17 Sep (four applications total). There was an average of 8 CEW moths captured per trap per night from first silk until several days before harvest. Silks were brown and dry shortly after 17 Sep.

On 1 Oct, up to 30 primary, market-sized ears were harvested within each plot. Efficacy of treatments was evaluated by recording the number of CEW, European corn borer (ECB), and Fall armyworm (FAW) larvae within each ear as well as the location of their collective damage, which was binned into three categories: 1) no feeding damage (= fresh market); 2) feeding damage to the ear tip only (the top inch or where developed kernels had made a complete ring) (=processing); or 3) damage from one inch below the ear tip to the ear base (= unmarketable). Data were analyzed using a generalized linear mixed model in SAS (ver. 9.4; PROC GLIMMIX) with treatment considered as a fixed effect and replication as a random factor in the model. Treatment means were compared using Tukey’s Studentized Range (HSD) Test at P < 0.05.

A majority of the larvae infesting ears in this trial was CEW (80%), followed by ECB (19%) and FAW (1%). Densities of CEW larvae per ear were significantly lower in plots treated with both rates of Entrust compared with densities in the untreated check (Table 1). None of the other treatments significantly reduced CEW densities compared with those in the untreated check. The average sum of ECB and FAW per ear in the 6 fl oz/acre rate of Entrust was significantly lower than the densities in the untreated check (Table 1). None of the other treatments significantly reduced the sum of ECB and FAW densities compared with those in the untreated check.

Feeding damage was moderate with 43 and 82% of the ears in the untreated check acceptable for fresh market and processing, respectively (Table 1). Sweet corn treated with both rates of Entrust had significantly higher percentages of fresh-market quality ears than those in the untreated check and all other treatments (Table 1). The percent of market-sized ears acceptable for processing was high in all treatments, but no treatment differed significantly from the untreated check (Table 1). This can be explained by the feeding habit of CEW, concentrated at the tip of the ear, which can be removed for processing. These results indicated that a total of four applications of Entrust timed at 3-d intervals spanning an 11-d period was highly effective for protecting the ears from this pest.¹

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