Effects of Different Application Rates of Cyantraniliprole on Control of Colorado Potato Beetle on Potato, 2017

The CPB has the ability to build up resistance to chemicals; therefore, it is important to test new chemistries and to monitor the efficacy of existing compounds. The experiment reported here compared two different lots of Verimark 20 SC applied at two rates and two gpa. Those were applied as an in-furrow application at time of planting. Admire Pro was used as an industry standard. The experiment was conducted in Presque Isle, ME in 2017 and replicated four times following RCB design. Plots for experiments 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.

Machine-cut ‘Atlantic’ seed was planted 25 May. A four-row Lockwood (Model 425) planter placed seed in an open furrow every 12 inches and delivered 14-14-14 fertilizer at the rate of 1,100 lb per acre. The rows were covered, placing the seed piece approximately three inches below the surface. Treatments nos. 2, 5, and 8 were applied at 5 gpa (TeeJet Nozzle TP8001VS), whereas treatments 3, 4, 6, 7, and 9 were applied at 20 gpa (Teejet nozzle TP8004VS). Tractor speed was 1.5 mph. The crop was treated with Bravo ZN at 5- to 7-day intervals based on recommendations from the University of Maine Cooperative Extension throughout the season for late blight control.

The numbers of insects were counted 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 was taken from 10 ft from the each of the inside two rows, for a total of 20-row ft. 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 Loam, pH 6.0. The total monthly rainfall for Jun, Jul, and Aug was, respectively, 3.86, 2.36, and 1.88 inches, and the mean temperature was 60, 65, and 63°F.

All treatments resulted in lower CPB numbers beginning on the third evaluation date compared with the untreated control plots (Table 1). Both lots and rates of Verimark showed season long control with a single in-furrow application. Applying chemicals at higher rates and higher gpa resulted in better CPB control. Admire Pro reduced CPB numbers, but to a smaller extent compared with Verimark applied at higher rate and higher gpa. All treatments reduced defoliation compared with the untreated check (Table 2). Yields were also generally higher on all treated plots than on the untreated check plots, although there was considerable variation among the treatments (Table 2). No phytotoxicity symptoms were observed following any of the insecticide treatment applications.

This research was supported by industry gifts of pesticide products and money.