Corn Rootworm Larval Control, 1996

Field: Agricultural and Biological Sciences (Life Sciences)

Abstract Rootworm, soil-insecticide test plots were established at 3 IA locations in 1996. Soil types were: Ames, silty clay loam; Cedar Rapids, silty loam, and Sutherland, silty loam. Plots were planted on areas that had been planted to trap crop (late-planted corn, high plant population) the previous year. The Sutherland location was planted no-till; the other 2 locations were conventional tillage. The tests with insecticide treatments were of 3 different types: (1) “experimental tests”—registered and numbered insecticides applied at planting time, (2) “yield tests”— only registered and EUP insecticides applied at planting time, (3) “cultivation tests”—registered and numbered insecticides applied at planting and/or cultivation time. A RCBD was used for all tests, with six replications for the “Cedar Rapids yield” test, and four replications for all others. Planting dates were: “Ames cultivation” 1 May, “Ames yield” 6 May, “Cedar Rapids yield” 22 May, and “Sutherland experimental” 8 May. 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 plantar. Planting-time liquid formulations were applied with a compressed-air delivery system built directly into the planter. The 2SC formulations were applied with a 8003E nozzle, delivering 13 gpa at 22 psi. Regent 80WG treatments were applied at 1 gpa using a #15 disk orifice placed inline and 16 psi. A steady stream of dilution was delivered in-furrow through a tube placed between the seed-furrow, disk-openers. 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, and positioned to deliver a 7-inch wide band around the base of the plants; 13 gpa at 25 psi. Broadcast applications of Furadan 4F 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 (experimental test only). Rootworm larval feeding was evaluated in late Jul by digging 3 roots from each treatment row and rating them 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 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 17.4 ft (0.001 acre) from each treatment at Ames, and machine harvesting 30 ft (0.0017 acre) at Cedar Rapids. To determine treatment differences, data were analyzed using ANOVA and means were separated with Ryan’s Q test (REGWQ).