Corn Rootworm Larval Control, 1997

Abstract

Abstract Rootworm, soil-insecticide test plots were established at 6 IA locations in 1997. Soil types were: Ames and Slater - silty clay loam; Cedar Rapids, Crawfordsville, and Sutherland - silty loam; and Nashua - loam. The Slater location had been continuous corn for several years. All other plots were planted on areas that had been planted to trap crop (late-planted corn, high plant population) the previous year. No-till tests were conducted at Crawfordsville and Sutherland. Insecticide treatments were tested in 1 or more of 3 different types of tests; (1) “experimental tests” - registered and developmental insecticides, (2) “yield tests” - only registered and EUP insecticides, (3) “cultivation tests” - registered and developmental insecticides applied at planting and/or post-emergence. A RCBD was used for all tests, with 8 replications for the “Sutherland conventional-till and no-till yield” tests, and 4 replications for all others. Planting dates were: “Ames cultivation and yield” 11 May, “Cedar Rapids yield” 6 May, “Crawfordsville experimental” 28 April, Nashua “experimental and cultivation” 6 May, “Slater experimental” 5 May, and “Sutherland yields” 12 May. Furadan 4°F applications dates ranged from 10 to 16 Jun. 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. Regent formulations were applied in-furrow through microtubes placed between the seed-furrow, disk-openers. A steady stream of dilution was delivered 1 gpa with 32 psi. Liquid cultivation-time insecticides were applied with a small-plot bicycle sprayer. Seven-inch basal treatments were applied using two 8002E nozzles, 1 on each side of the corn row, positioned to deliver a 7-inch-wide band around the base of the plants (13 gpa at 22 psi). Broadcast applications of Furadan 4°F were applied to single rows. A boom containing three 8002SV nozzles (19-inch centers) delivered 13 gpa at 30 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. Tygon 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 measuring extended leaf heights on 5 consecutive plants and taking stand counts from 0.0001 acre (experimental test only). Rootworm larval feeding was evaluated in mid to late Jul by digging 3 roots from each treatment row and rating their damage on the Iowa 1-6 scale (1 = no damage or only a few minor feeding scars; 6 = 3 or more nodes of roots completely destroyed). Lodging counts were taken at har-vest 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 also taken in the yield plots at harvest time. Yields were measured by hand harvesting 17.4 row-ft from each treatment at Ames, and machine harvesting 25 row-ft at Cedar Rapids and Sutherland. To determine treatment differences, data were analyzed using ANOVA and means were separated with Ryan’s Q test (REGWQ).