Control of Colorado Potato Beetle in the Red River Valley, Grand Forks, ND, 1994

Potatoes were planted 17 May at the Research Farm of the Red River Valley Potato Growers Association. Plots were four rows wide, 60 ft long, with 38 in rows and 12 in between plants. Plots were separated on all sides by 6.3 ft of cultivated soil. The experiment had a complete randomized plot design with four replications. Egg masses were flagged 15 Jun and checked daily. Thirty percent egg hatch was estimated to have occurred 22 Jun, but heavy rains and wet field conditions delayed first application of insecticidal sprays until 24 Jun. Subsequent spray applications were made 5, 12 Jul, and 8 Aug. Jun and Jul sprays were targeted against first generation larvae, Aug application against summer generation adults. All applications were made using a tractor-mounted boom sprayer, with a single Teejet nozzle over each row. Sprays were applied in 40 gal of water/acre at 40 psi. Egg masses, small larvae (1st and 2nd instar), large larvae (3rd and 4th instar), and adults were counted 27 Jun, 7, 14 Jul, and 10 Aug on 20 randomly selected plants from the two middle rows of each plot. Tuber yields were estimated by mechanical harvesting one row per plot 2 Sept. Defoliation data were recorded at each evaluation and expressed as mean percent of defoliation across sampling dates. The average number of insect counts across sampling dates are presented in the table. Best control resulted from the use of Furadan, Imidan, and Capture. Yield differences among treatments were not significantly correlated with any measure of insect numbers. Parts of the field were saturated for an extended period of time by heavy Jun rains, which adversely affected yields in all plots. Tuber yields ranged from 136.7 to 207.4 cwt/acre.