Corn Rootworm Larval Control in Iowa, 1993

Abstract

Abstract Rootworm planting-time, soil-insecticide test plots were established at 6 locations in 1993. Soil types were: Ames and Rhodes, silty clay loam; Nashua, loam; Newell and Waukee, clay loam; and Sutherland, silty clay. All plots were planted on areas that had been planted to trap crop (late-planted corn, heavy stand) the previous year. A RCB design, with 4 replications for the root-protection trials (registered and numbered products) and 8 replications for the yield trials (registered and EUP products) 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 10 gpa at 23 psi. Chemical phytotoxicity was checked in early Jun by taking stand counts from 1/1000 acre and measuring extended leaf heights on 10 consecutive plants. Rootworm larval feeding was evaluated in late Jul and Aug 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. To determine treatment differences, data were analyzed using ANOVA and means were separated with Ryan’s Q test (REGWQ).