Comparing 2 Soil Systemics and 2 Foliars in 10 Regimes for Control of Pyrethroid-Resistant Colorado Potato Beetle, 1987

The trial was located at the Northwest Experiment Station, Crookston, Minn. The major objective of the 1987 insecticide trials was to compare at-plant-and-time-of-emergence soil systemic treatments in dryland sites (Crookston, Minn., and Grand Forks, N. Dak.) and irrigated locations (Park Rapids and Brooten, Minn.). Soil systemic treatments were present at each site with various combinations of foliars. CPB are at least 100-fold resistant to Pydrin and 40-fold resistant to Ambush + Pounce at this location. Plots were 4 40-inch rows 25 ft long. Treatments were replicated 4 times and were arranged in a randomized complete block design. B-size Norchip seed was planted on 5 May and planting treatments of Temik and Thimet applied over the row. The soil was a clay type, permitting granules to fall into soil openings along the planting ridge. Soil moisture was very good. Emergence treatments were applied on 29 May when potato plants were 2 inches high. Soil was cultivated over the emergence treatment. Wintering CPB adults were present in higher than normal numbers on this date. Foliars were applied on 20 and 28 Jun, 10 and 22 Jul, and 8 Aug according to an experimental plan of 1, 3, and 5 foliars. Foliars applied over the emergence soil systemic were applied 20 Jun and 8 Aug. Adult emergence from an adjacent potato plot threatened to overwhelm these studies in July (note adult defoliation column in table). Thus, we waited for modest second-generation oviposition and then treated the entire study with 0.5 lb (AI)/acre of Penncap-M on 24 Jul. Three applications of fungicide were applied independently of insecticides. Yields were taken from the center 2 plot rows, graded #1 and B-size, weighed, and recorded.