Control of Colorado Potato Beetle with Trigard, 1991

Two fields in Bay Co., MI, were selected for trials using the insect growth regulator Trigard against CPB. ‘Onaway’ potatoes were planted on 17 Apr 1991, and 3 May 1991, respectively, and were managed by growers Brian Hugo and Jim Kryszak. Plots measuring 14 rows wide by 60 feet long were established in each field on 7 Jun in a randomized complete block design with 4 replications. Treatments were: 0.125 lb (AI)/acre (low rate); 0.25 lb (AI)/acre (medium rate); and 0.375 lb (AI)/acre (high rate; and an untreated control. The fields were sprayed on 7 and 19 Jun using a tractor mounted boom sprayer at 25 gal/acre and 40 psi. A maintenance spray program using insecticides effective against adult beetles was started on all plots the second week of Jul, after the summer adults had emerged. A pre-spray count of CPB egg masses, adults, and small and large larvae from one or two plants per plot was taken on 7 Jun. High numbers of large larvae were already present in the Hugo field at this time. Four plants per plot were sampled on 13, 20, 27 Jun and 2 Jul. On 2 Jul a qualitative defoliation rating was given to each plot based on the percent of plants in each of five defoliation categories. Potatoes were harvested from two 10-ft sections of row per plot in 19 Aug, sized and weighed.