Efficacy of Selected Insecticides for Sod Webworm Management in Fine Fescue for Seed Crops, 2020

The performance of selected foliar insecticide treatments against sod webworm in cool-season grasses grown for seed crops in Oregon was evaluated. This experiment was performed in a commercial strong creeping red fescue, Festuca rubra L. subsp. rubra field site near Silverton, OR (44.874392 latitude, −122.800546 longitude). The field was planted in spring 2016 to the cultivar ‘Kent’. Seeding rate was 6 pounds per acre, with a 7.5-inch row spacing and 0.75-inch seeding depth. The experimental plots were 30 ft long by 10 ft wide, each plot was separated by a 10 foot buffer. The experimental design was a randomized complete block with four replications. The treatments are listed in Table 1. Foliar insecticide treatments were applied on 22 Sep and 16 Oct, 2020 using a CO₂-pressurized backpack sprayer (Bellspray Inc., Opelousas, LA) at a spray volume of 20 gpa at 24 psi through (QJ8360) Quick TeeJet nozzles. Insect counts for sod webworm were taken post-application from three, 6-inch cores to a depth of 4 inches. Cores were removed from each plot and each core was dissected for live, dead, and moribund larvae and pre-pupae. Data were analyzed by ANOVA, and means were separated using Fisher’s protected LSD (P ≤ 0.05).

On 29 Sep, significantly fewer sod webworm larvae were present in plots treated with Prevathon SC (all rates), Dimethoate 400EC, Endigo ZCX, and Avaunt eVO compared to an untreated check (Table 1). This efficacy against sod webworm was comparable to the grower standard treatment of Lorsban Advanced. Conversely, there was no significant reduction in larvae per core between plots treated with Brigade 2EC (both rates), Sevin XLR, and the untreated check. On 5 Oct, all treatments had significantly fewer sod webworm compared to the untreated check, except for Dimethoate 400EC and Brigade 2EC (both rates). On 19 Oct, a significant reduction in larvae count was observed in all Prevathon SC plots irrespective of the rates and application timing used in this study. The efficacy of Prevathon SC was comparable to the standard treatment of Lorsban Advanced. No phytotoxicity or differences in plant vigor were observed with any insecticide treatment.¹

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