Colorado potato beetle control in potato with tolfenpyrad in combination with adjuvants, 2023

Adjuvants may affect the efficacy of active ingredients. Having effective insecticides is especially important for the CPB because of its high propensity to evolve resistance to chemicals. The experiment was conducted in Presque Isle, ME, in 2023 and replicated 4 times. The experiment followed the RCB design. Plots were four rows wide (12 ft) and 30 ft long. A 10 ft space was left fallow between blocks, and a 6 ft space was left fallow between the plots within the blocks.

Machine-cut ‘Reba’ seed was planted on 24 May. A 4-row Lockwood (Model 425) planter placed seed in an open furrow every 12 inches and delivered 14-14-14 fertilizer at 1,100 lbs. per acre. The rows were mechanically covered, placing the seed piece approximately 3 inches below the surface. On 5 Jul, a single foliar insecticide application was made using a modified Century boom sprayer, 8 Turbo Twinjet (TTJ60-11005) nozzles per plot, 20 gpa at 30 psi, boom height 20-24 inches, and 4.3 mph tractor speed. The crop was treated with Bravo Weather Stik on a 7-day interval based on recommendations from the University of Maine Cooperative Extension throughout the season for late blight control.

The number of insects was counted on 5 plants randomly selected on every plot from each of the 2 inside rows, for a total of 10 plants per plot. Potato defoliation was quantified by visually estimating the percentage of foliage missing on each plot due to beetle damage. When dates of count and application were the same, counts were made before applications of the insecticide. Data were transformed using log₁₀(X + 1) for insect counts and arcsine square roots for defoliation. ANOVA was conducted, and means were compared using Fisher’s LSD test. Means followed by the same letter do not significantly differ from each other (P > 0.05).

The soil is classified as Caribou Loam, pH 6.0. The total monthly rainfall for Jun, Jul, and Aug (through 25 Aug) was respectively 5.38”, 4.06”, and 6.26”, and the mean temperature was 61.2, 71.6, and 63.32 °F.

This experiment was used to determine whether Hydrovant used in combination with either Exponent or Dyne-Amic affects efficacy of Torac 15EC against the CPB. All treatments provided a significant season-long reduction in the CPB numbers (Table 1) and defoliation (Table 2) compared with the untreated control. Beetle counts and defoliation were slightly higher when Torac 15EC was applied in combination with Dyne-Amic and Hydrovant compared with applications in combination with Exponent and Hydrovant or in combination with Exponent and Dyne-Amic. Yields on all treated plots were significantly increased compared with the untreated control, but not affected by the adjuvants.

Phytotoxicity was not observed following the insecticide treatment applications.¹

Dyne-amic: Modified Vegetable Oil Surfactant Blend

Hydrovant: Polyvinyl Alcohol

Exponent: Piperonyl Butoxide (PBO)

Torac 15 EC: Tolfenpyrad

Footnotes