Evaluation of Dimilin 1% Bran Bait for Grasshopper Control on Rangeland, 1990

A 150-acre area of rangeland near Edgemont, S. Dak. was chosen for evaluating efficacy of Dimilin (diflubenzuron) 1.0% bran bait against rangeland grasshoppers. The vegetation in the test site was dominated by cool and warm season perennial grasses. Percent basal coverage by all plant species ranged from 45-60%. The test site was divided into 9 contiguous plots of 12 acres. Pre- and posttreatment grasshopper densities were assessed by counting grasshoppers in 40, 0.1 m2 rings located in the center of each plot. Before application of treatments, Aulocara elliotti were 20% second, 40% third and 25% fourth instars, and Ageneotettix deorum and Amphitornus coloradus were 70% second and 30% third instars and the 3 species respectively constituted 53, 22 and 10% of the grasshopper population in the study site. Treatments were replicated 3 times in a randomized complete block design. The 9 plots were grouped into 3 blocks with grasshopper population estimates recorded using 1 d pretreatment counts. Dimilin bait was applied at 1.0 and 2.0 lb of bran flakes/acre rates from a Brie-Mar Model 60 bran applicator mounted on a pickup truck on 19 Jun and calibrations were based on a 13 m swath. Posttreatment counts were conducted 7, 14, 21 and 28 DAT. The natural change in grasshopper densities was determined by counts from untreated plots. Percent survival based on pretreatment counts on the same treated plot was adjusted for the natural population fluctuations by a modified Abbott's formula and expressed as percent grasshopper reduction.