Evaluation of Torac, Warrior, and Coragen for First-Generation Colorado Potato Beetle Management in Wisconsin, 2019

This trial was performed to evaluate the first-generation Colorado potato beetle control of Torac and Torac + PBO Twin-Pack relative to industry standards and an untreated check. This trial was conducted at the University of Wisconsin’s Hancock Agricultural Research Station, located 1.1 miles west of Hancock, Wisconsin (44.112332°N, −89.534886°W), on a loamy sand soil in 2019. Potato Solanum tuberosum cv. ‘Yukon Gold’ B-size tubers were machine planted as a solid planting on April 16, 2019. Four replicates of eight experimental plots were arranged in an RCBD region. Plots measured two rows (6 ft) wide by 20 ft long. Plots were separated by one untreated guard row and 8 ft of tilled ground along rows. The entire trial measured 108 ft wide (including a 12 ft drive alley along the center) by 120 ft long. Standard fertilizer inputs and fungicide treatments were applied to maintain plant health. Experimental insecticide treatments included Torac at a low and high rate, Torac + piperonyl butoxide (PBO), Torac + Warrior II, Warrior II, and Coragen. All treatments included either Silwet, NuFilm P, or methylated seed oil (MSO) added at 0.25% v/v as adjuvants. Foliar applications were performed on Jun 19 after 50% CPB egg hatch was observed, and reapplied 7 d later on Jun 26. Applications were made using a CO2-pressurized backpack sprayer operating at 30 psi, equipped with a 6 ft boom with 4 flat-fan nozzles (TeeJet XR8002VS) spaced 18 in. apart, and delivering 20 gal/ac while travelling at 3.5 ft/s Colorado Potato Beetle (CPB), Leptinotarsa decemlineata, populations were assessed on 10 randomly selected plants in the center of each plot for the following life stages: adults, egg masses, small larvae (first and second instars), and large larvae (third and fourth instars). CPB counts were performed 2, 6, 13, 22, and 27 d after initial foliar treatment applications. Insect counts were log(x + 1) transformed and percent defoliation ratings were arcsine square root transformed prior to statistical analysis to satisfy assumptions of normality. Treatment main effects were determined using ANOVA. Means separation letter codes were generated using Tukey’s HSD procedure (α = 0.05). All plots achieved high levels of emergence and colonization and no signs of phytotoxicity were observed among any of the treatments. First-generation (21 Jun, 25 Jun, 2 Jul) CPB adult counts were generally low and did not vary significantly between treatments (Table 1), except on 2 Jul (P = 0.03). Second-generation (11 Jul, 16 Jul) adult counts were higher on 11 Jul in the experimental treatments relative to the check and significantly higher on 16 Jul (P < 0.0001) due to complete defoliation of the check plots by that time. Peak small larvae (first and second instar) activity occurred on 21 Jun, 25 Jun, and 2 Jul (Table 2), with the Torac + Warrior II treatment performing significantly better than the check on 21 Jun (P = 0.05), the Torac + PBO, Torac + Warrior II, and Coragen treatments outperforming the check on 25 Jun (P = 0.01), and only the Coragen treatment outperforming the check on 2 Jul (P < 0.0001). Peak large larvae activity was observed on 2 Jul and 11 Jul (Table 3), with only the Coragen treatment outperforming the check on 2 Jul (P < 0.0001). On 11 Jul, both the Torac + PBO and Coragen treatments kept large larvae numbers significantly lower than the other experimental treatments (P < 0.0001), but the untreated check plots were completely defoliated at this point, so no comparison to the check can be made for this date. Large differences in plot defoliation were observed starting on 2 Jul (Table 4), with all experimental treatments performing significantly better than the check (P < 0.0001). On 11 Jul, the check plots were completely defoliated, while the lowest defoliation was observed in the Torac + PBO, Torac (high rate), and Coragen plots (P<.0001). By 16 Jul, only the Coragen treatment was maintaining low levels of defoliation (5%), with all other treatments greater than 50% defoliation (P < 0.0001). Overall the Coragen treatment had the best performance well into the second generation, followed by the Torac + PBO treatment, which began to fail by the last count date (16 Jul).1 Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05). *P-value followed by an asterisk indicates a significant block effect. aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05). *P-value followed by an asterisk indicates a significant block effect. aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05) aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05) aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05) aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05) aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05). *P-value followed by an asterisk indicates a significant block effect. aUntreated plots were completely defoliated by 11 Jul. Means followed by same letter code are not significantly different (Tukey’s HSD, α = 0.05). *P-value followed by an asterisk indicates a significant block effect. aUntreated plots were completely defoliated by 11 Jul.

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