Ground Application of Dimilin 1.0% Bran Bait to Rangeland Grasshoppers, 1991

A 160-acre pasture near Belle Fourche, SD was chosen for evaluating the efficacy of Dimilin (diflubenzuron) 1.0% bait to rangeland grasshoppers. Major forage species in the site were cool and warm-season perennial grasses. Basal coverage by all plants ranged from 50 to 70%. The site was divided into 16 contiguous plots of ten acres. Pre- and posttreatment densities were assessed by grasshopper counts in 40, 0.1 m2 rings arranged in a circle in the center of the plot. Before the treatments, Aulocara elliotti were 50% 2nd and 30% 3rd instars, M. confusus were 10% 3rd, 20% 4th and 50% 5th instars, and M. bivittatus were 60% 2nd instars. These three species respectively constituted 60, 15, and 10% of the grasshopper population in the site. Treatments were replicated 4 times in a RCB. The 16 plots were grouped into four blocks using 1-day pretreatment counts. The bait was applied on 14-15 Jun. The delivery system consisted of a Brie-Mar Model 60 bran applicator mounted on a pickup truck and provided a 13 m swath. Grasshopper counts were conducted 7, 14, 21, 28, and 60 DAT. Natural change in grasshopper densities was determined by counts from untreated plots. Posttreatment survival rates based on pretreatment counts on the same treated plots were adjusted for natural population fluctuations by a modified Abbott's formula and expressed as percent grasshopper reduction. Prior to treatment, the average grasshopper density in untreated plots was lower than that in plots to be treated.