Field evaluation of a reduced rate of carbaryl spray on rangeland grasshoppers (Orthoptera: Acrididae)

A modified formulation of carbaryl insecticide was aerially applied to contiguous 65-ha plots of rangeland in South Dakota in 1989. The application rate contained 25% less active ingredient than the standard formulation used in the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) rangeland grasshopper program. The experimental plan was a four-replicate randomized block design with the experimental plots grouped by pretreatment grasshopper densities. Reduced rates of application resulted in control statistically equal to the standard carbaryl rate. Within 7 days of treatment, grasshopper populations were reduced by 95% or more for each of the treatments. The four dominant grasshopper species, comprising 81.5% of the overall population, were each significantly reduced by all of the treatments after one week.