Evaluation of Several Seed Treatment and In-Furrow Programs for First-Generation Colorado Potato Beetle Management on Potato in Wisconsin, 2021

This trial was conducted in 2021 at the University of Wisconsin’s Hancock Agricultural Research Station, located 1.1 miles west of Hancock, Wisconsin, in field E-21 (44.115173, −89.534804) on a loamy sand soil. Four replicate blocks of 7 treatment plots including an untreated control plot were arranged in a randomized complete block design. Plots measured 4 rows wide by 20 ft long with rows spaced on 3 ft centers. Potato, Solanum tuberosum cv. ‘Snowden’ B-size uncut tubers were hand-planted in opened rows on Apr 26. Seed was placed approximately 12 inches apart along rows. Furrows were closed after in-furrow applications were completed. Plots were separated by two unplanted guard rows or 8 ft of bare ground separating experimental replicates. The entire trial measured 16 rows (48 ft) wide by 272 ft long. Plots were maintained according to standard commercial practices including fertilizer, herbicide, and fungicide applications. The untreated control received no insecticide application. Seed treatment was completed the day prior to planting by tumbling seed in a 6.0 ft⁻³ small, concrete mixer and introducing the required quantity of product using a backpack sprayer delivering 115 ml diluent to 50 cwt of seed. In-furrow treatments were applied using a CO₂-pressurized backpack sprayer equipped with a 3 ft boom, operating at 30 psi and delivering 11.1 gal/acre through 2 flat-fan nozzles (Tee Jet XR 8002-VS) spaced 18 inches apart while travelling at 3.5 ft/s. In-furrow applications were performed on the exposed seed before closing the furrows. All plots achieved high levels of emergence and no signs of treatment-related phytotoxicity or reduced plant vigor were observed.

Colorado potato beetle (CPB), Leptinotarsa decemlineata, populations were assessed weekly on 10 randomly selected plants in the center of each plot for the following life stages: adults, egg masses, small larvae (1st–2nd instars), and large larvae (3rd–4th instars). Insect counts were performed on Jun 3, 10, 21, 28, and Jul 8 (38, 45, 56, 63, and 73 days after planting). To determine yield and tuber quality, a single 20 ft-long row from each plot was harvested on Sep 2. Tubers were graded using an AgRay Vision X-Ray grading machine which generated electronic measurements of tuber size and weight. The second largest value of a tuber’s dimension in the X, Y, and Z directions was considered its ‘diameter’ and compared against the following USDA classification scheme: A-size tubers are larger than or equal to 1.875 inch diameter, B-size tubers fall between 1.875 and 1.5 inches, and C-size tubers fall below 1.5 inch diameter.

Data analysis was performed in R version 4.1.0 (R Core Team, 2021). Insect counts were log(x+1) transformed prior to statistical analysis to satisfy assumptions of normality. Defoliation percentages were arcsine square root transformed. Treatment main effects were determined using analysis of variance. Means separation letter codes were generated using Tukey’s HSD procedure (α = 0.05, R package ‘agricolae’, Mendiburu 2021).

The portion of the Hancock Agricultural Research Station where this trial took place generally experiences very high CPB pressure, which is useful in comparing treatment effects, but often results in untreated plots being overwhelmed and defoliated quickly, making comparisons versus control difficult at later dates. Peak first-generation (overwintering) colonizing CPB adult counts were observed on Jun 3 and 10 (Table 1), with Platinum and Belay having among the lowest counts. Peak small larvae counts were observed on Jun 10 and 21 (Table 2), with the best control observed in the Verimark in-furrow, Platinum, and Belay treatments. Large larvae populations peaked on Jun 21 and 28 (Table 3) and were lowest in the Belay treatments, followed by Platinum, then Verimark in-furrow. Defoliation estimates (Table 4) support these trends, with low amounts of defoliation observed in the Platinum and Belay treatments. However, despite higher CPB adult and larval counts on plants relative to the Platinum and Belay treatments, low defoliation pressure was observed in both Verimark treatments, and only moderate defoliation pressure was observed in the Admire Pro treatment. Only the untreated and the Sivanto plots ended the trial with high levels of defoliation (approaching 50%). Overall, the best first-generation CPB control in this trial came from the three neonicotinoid products Platinum (thiamethoxam), Belay (clothianidin), and Admire Pro (imidacloprid), followed by Verimark (cyantraniliprole), with poor first-generation control observed with Sivanto (flupyradifurone).¹

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