Northern and Western Corn Rootworm Adult Emergence and Root Injury Ratings Associated with Labeled and Reduced Soil Insecticide Application Rates in Aurora, Sd, 1994

Abstract

Abstract A dryland continuous corn site in east central SD was selected to measure northern and western corn rootworm adult beetle emergence from corn plots treated with planting-time soil insecticides. In addition to beetle emergence, treatment efficacy in preventing larval root feeding injury was also evaluated. Treatments included labeled and reduced application rates of 3 compounds arranged in a RCBD with 4 replications. Individual treatment plots consisted of single 15.2-m long rows spaced 96.5 cm apart. All insecticide treatments were applied in-furrow at planting time by directing granules between double-disk openers and into the open seed furrow. Delivery of granules was regulated using Noble metering units mounted on a specially adapted Kinze 4-row corn planter. All units were calibrated on the planter before insecticide applications. Plant injury evaluations consisted of extricating 5 roots per plot examining them for feeding injury, and rating them in accordance with the Iowa State 1 to 6 scale. Prior to rootworm beetle emergence, two 0.6 m wide by 1.0 m long by 15.2 cm high cages were placed (equidistant from each other and the end of the plot) over each treatment row. The exterior rectangular frame base of each cage was constructed of 26-gauge galvanized steel and the top was made of aluminum screening material (45-mesh per cm2). Screens were supported by galvanized steel strips that terminated at a central point (approximately 20.3 cm) above the frame to form a screened pyramid. All interior screen margins and seams were sealed with silicone rubber caulking material. The pyramidal shape of cage tops was designed to exploit the natural negatively geotactic response (crawling upward) of newly emerged beetles. A plastic cylindrical capture device was positioned at the apex of each screened pyramid to catch beetles as they crawled upward on the screened cage top, and an inverted aluminum screen cone was fastened to the bottom side of each capture device to prevent beetles from returning into the cage. Cages were monitored at 2-d intervals for the entire beetle emergence period. Monitoring consisted of collecting all beetles for the respective treatments from each replicate, and returning them to the laboratory for processing. Laboratory processing consisted of identification of emerged adults by sex and species respective to treatments. All data (root injury ratings and adult emergence) were analyzed with SAS’s General Linear Models procedure and means were compared using DMRT.