Efficacy of Neonicotinoid Insecticides Controlling Aphids and Colorado Potato Beetle in Potatoes Grown Under Central Pivot Irrigation, 2018

The objective of this study was to evaluate the efficacy of registered insecticides for control of several species of aphids, including the green peach aphid (Sulzer) and potato aphid Macrosiphum euphorbiae Thomas, and the Colorado potato beetle Leptinotarsa decemlineata Say, in potatoes grown under central pivot irrigation in the Columbia Basin of Oregon. ‘Ranger Russet’ potatoes were planted into single rows on 32-inch (81.28 cm) centers with 9-inch (22.86 cm) plant spacing on 20 Apr 2017. Plots were 4 rows wide and 25 ft long (7.6 m) with a 5 ft (1.5 m) buffer between plots. The potato crop was established by withholding water until emergence and then irrigating with 1-inch (2.5 cm) overhead irrigation using a standard center-pivot irrigation system to replicate commercial growing practices in the region. Each treatment was replicated 4 times, and plots were arranged in an RCB. Potato seeds used in the seed treatment were treated by placing tubers in a Yardmax 4.0 cu. ft (113.27 l) concrete mixer. In-furrow treatments were applied using a backpack sprayer with TeeJet AI8002 nozzles at 40-psi solution and 30 gpa (280.6 liter/h); rows were immediately covered afterwards. Potatoes emerged on 16 May. Aphids were counted, by shaking 10 plants per treatment plot, into small 8-inch wide (20.32 cm) × 6-inch depth (15.24 cm) buckets (Table 1). Colorado potato beetles were sampled by selecting 10 random plants per treatment plot; adults, larvae, and egg masses were counted but due to low numbers, data were pooled together. Insect counts started at plant emergence and continued through the season ending at 84 days after emergence (DAE). Data were log-transformed (mean + 1) and were arcsine-transformed prior to the ANOVA and F-protected LSD (P ≤ 0.05) to distinguish treatment mean differences.

In general, none of the treatments statistically differed from the untreated check throughout the trial, although numerical differences were observed. There was low aphid pressure during the trial ranging from 0 to 0.15 aphids/plant. First aphids were found 28 DAE in the untreated check. A week later, aphids were found in all treatment plots regardless if they were seed or in-furrow treated. Colorado potato beetle egg masses, larvae, or adult numbers ranged from 0 to 0.10 Colorado potato beetle/plant. They were found in the untreated check plots 28 DAE. A week later, they were found in the seed treatment plots; two weeks later, they were found in the in-furrow–treated plots. No statistical differences were observed among treatments, although numerical differences were observed (Table 2).

This research was supported by industry in kind-gifts.