Control of Insects on Potato, 2016*

Testing new chemistries and monitoring the efficacy of existing compounds is extremely important because the CPB has the ability to build up resistance to chemicals. The experiments were conducted in Presque Isle, ME in 2016 and replicated four times (unless otherwise noted). The experimental design was RCB. Plots for experiments reported in Tables 1 and 2 were eight rows wide (24 ft) and 50-ft long. Plots for experiments reported in Tables 3 and 4 were four rows wide (12 ft) and 50-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.

The crop was planted between 25 and 26 May using machine cut ‘Superior’ potato seed. A John Deere 216 two row potato planter was used to make open furrows applying 1,100 pounds of 14–14–14 fertilizer per acre. The seed was hand placed at 12 in. spacing. The rows were mechanically covered, placing the seed piece ∼3 in. below the surface. In-furrow treatments (Tables 1 and 2) were applied at the time of row closure using a custom-built sprayer, one nozzle per row, 8 in. band, 4.0 gpa at 12 psi, and 1.5 mph tractor speed. Foliar insecticide applications were made with a modified Century boom sprayer, eight nozzles per rep, 40 gpa at 35 psi, boom height 20–24 in., and 3.0 mph tractor speed. The crop was treated with Bravo ZN at 5–7 d intervals based on recommendations from the University of Maine Cooperative Extension throughout the season for late blight control.

Insect counts were conducted weekly on 10 plants selected randomly from the center two rows of each plot. When dates of count and application were the same, counts were made prior to applications of the insecticide. Data were transformed using log₁₀(X + 1) for insect counts and arcsine square roots for defoliation. Yield data were not transformed. ANOVA were 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 was classified as Caribou Gravely Silt Loam, pH 6.0. The total monthly rainfall for June, July, and August was, respectively, 3.51, 5.77, and 5.12 in., and the mean temperature was 61, 66, and 65°F, respectively.

The experiment presented in Table 1 (three replications) compared Verimark 20 SC as an in-furrow application at time of planting with two foliar insecticide applications later in the growing season. All treatments resulted in lower CPB numbers compared with the untreated control plots (Table 2). Verimark showed season long control with one in-furrow application. Two foliar applications of Exirel had a similar effect. Blackhawk reduced CPB numbers, but to a smaller extent compared with the other two insecticides. All treatments reduced defoliation compared with the untreated check (Table 2). Yields were also higher on all treated plots than on the untreated control plots (Table 2).

All chemical treatments reduced the CPB population compared with the untreated control after one application, although beetle populations on plots treated with Besiege were higher compared with the plots treated with the other two chemicals (Table 3). The second applications of Exirel and Besiege did not improve control over single applications of the same chemical (Table 3). All chemicals reduced the amount of damage done to the foliage (Table 4). No statistically significant differences were detected among the yields (Table 4).

No phytotoxicity symptoms were observed following any of the insecticide treatment applications.

Author notes