Evaluation of foliar programs for first-generation Colorado potato beetle management, 2023

This trial was conducted at the University of Wisconsin’s Hancock Agricultural Research Station on field E-29 (GPS: 44.113315, −89.535734) on a Plainfield sand soil (PfA) in 2023. Potato, Solanum tuberosum cv. ‘Snowden’ B-size tubers were machine planted on 24 Apr with an approximate seed spacing of 12 inches and a row spacing of 3 ft. Fertilizer granules (6-30-22-4S + micros at 550 lb/acre) containing no insecticide were introduced at the time of planting per standard commercial practices. The solid-planted field was later divided into 2 row by 20 ft-long plots by tilling 8 ft alleys across rows with adjacent plots separated by one untreated guard row. Due to the large number of treatments, the field was separated into 2 blocks of 12 and 11 treatments, respectively, with each block including an untreated control. Plots were arranged in an RCB design with 4 replicates. Plots were maintained according to standard commercial practices including fertilizer, fungicide, and herbicide applications. Treatments were initiated at either 10% egg hatch (7 Jun, 3× foliar applications) or 50% egg hatch (14 Jun, 2× foliar applications). All treatments were applied using a CO₂-pressurized backpack sprayer fitted with a 6 ft boom, operating at 30 psi and delivering approximately 20 gpa through 4 flat-fan nozzles (Tee Jet 8001VS) while traveling at 3 mph. See Table 1 for complete treatment details.

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–second instars), and large larvae (third–fourth instars). CPB counts and whole-plot defoliation estimates were performed on 9, 16, 19, 26 Jun, and 5 Jul (2, 5, 8, 12, 21 days after Appl. B). Aphid and potato leafhopper nymph counts were performed on 23 Jun to evaluate performance against piercing-sucking insects. Evaluation data were analyzed in R version 4.3 (R Core Team, 2023). Insect counts were log(x + 1) transformed, and defoliation percentages were arcsine square root transformed prior to statistical analysis. 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”).

This trial was placed in a portion of the Hancock Research Station with typically very high CPB pressure, and this year was no exception. Without the application of effective insecticides, first-generation beetles will typically completely defoliate a plot. All treatment programs in this trial controlled defoliation from CPB significantly better than the untreated control plots, though some treatments were more effective than others (Table 2). First-generation (overwintering) adult CPB counts show modest differences between treatments until second-generation adult emergence on 5 Jul, when the complete defoliation of the untreated plots led to very low CPB counts in those treatments (Table 3). Small larvae populations differed substantially between treatments, with notably low cumulative counts in treatments containing Avaunt eVo (14, 15). Large larvae populations were adequately controlled by most of the treatments, though counts were higher in Trt 4 (Torac without Exponent), the low rate of Plemax (Trt 5), both Rimon treatments (11, 13), the low rate of Coragen (Trt 20), and both Calantha programs (Trt 22, 23). Among the most effective treatment programs were Avaunt eVo + Exponent (Trt 14), Torac + Exponent + Hydrovant (Trt 3), Vantacor (Trt 18, 19), Harvanta (Trt 9, 10), and Elevest (Trt 16, 17). The Rimon treatments (Trt 10, 13, 14) were generally not as effective as others, except for Trt 15, which also contained Avaunt eVo + Exponent and was slightly more effective than Trt 14, which did not contain Rimon. The Torac treatment without Exponent (Trt 4) was not as effective as the Torac treatments with Exponent (Trt 2, 3). Calantha (Trt 22, 23), a novel RNAi-based CPB-specific insecticide, was relatively effective but has only about a week of residual activity so was losing efficacy by 5 Jul (16 days after the last application). Aphid and leafhopper pressure was low, and there were no significant differences between treatments (data not shown).¹

Footnotes