Corn Rootworm Larval Control, 1994

Abstract

Abstract Rootworm planting-time, soil-insecticide test plots were established at 3 IA locations in 1994. Soil types were: Ames (Chapin), silty clay loam; Nashua, loam; and Sutherland, silty clay. Plots were planted 9, 2 and 3 May, respectively, on areas that had been planted to trap crop (late-planted corn, high plant population) the previous year. A RCBD with 4 replications for the experimental and cultivation tests and 8 replications for the yield trials was used. All treatments were applied to single 50-ft length rows with 30-inch row spacing. Granular insecticide formulations were applied with modified Noble metering units mounted on a 4-row John Deere 7100 planter. Planting-time liquid formulations were applied with a compressed-air delivery system built directly into the planter; 8003E nozzles delivered 13 gpa at 23 psi. Liquid cultivation-time insecticides were applied with a small-plot bicycle sprayer. Two 8002E nozzles, 1 on each side of the corn row, were positioned to deliver either a 7 or 15-inch band width around the base of the plants; 13 gpa at 25 psi. Broadcast (30-inch band) applications of Furadan 4F were applied to single rows. A boom containing three 8002 nozzles (19-inch centers) delivered 13 gpa at 32 psi. One untreated buffer row was left on each side of a “broadcasted” row. Granular cultivation-time insecticide applications were made with electrically-driven Noble units mounted on the tool bar of a 2-row, rear-mounted cultivator. Plastic tubes, positioned directly in front of the cultivator sweeps, directed the insecticide granules to both sides of the corn row for basal treatments. Chemical phytotoxicity was checked in early Jun by taking stand counts from 1/1000 acre and measuring extended leaf heights on 10 consecutive plants (experimental tests only). Rootworm larval feeding was evaluated in Jul by digging 5 roots from each treatment row and rating them on the Iowa 1-6 scale (1 equal to no damage or only a few minor feeding scars, and a 6 rating equal to 3 or more nodes of roots completely destroyed). Lodging counts were taken at harvest time. A plant was considered lodged if the angle between the base of the plant and the ground was 45° or less. Stand counts were taken in the yield plots at harvest time. Yields were measured by hand harvesting 1/1000 acre from each treatment at Nashua and Chapin, and machine harvesting 25 row-ft at Sutherland. To determine treatment differences, data were analyzed using ANOVA and means were separated with Ryan’s Q test (REGWQ).