Field Corn, Corn Rootworm Larval Control, 1987

Abstract

Abstract Planting-time, soil insecticide test plots were established at 7 Iowa locations in 1987. The experimental design was a randomized complete block with 4 replications for the root protection trials and 6 replications for the yield trials. All treatments were applied to 50-ft rows spaced 30 inches. The yield trials had double-row treatments. All other trials had single-row treatments. Granular insecticide formulations were applied with modified Noble metering units that had been laboratory-calibrated to deliver material accurately at a tractor speed of 4 mph. The applicators were mounted on a 4-row John Deere Max-Emerge 7100 integral planter equipped with ripple coulters. Each row was constantly monitored to ensure that insecticide was correctly applied at all times. Drag chains were used for incorporation. Liquid insecticide formulations were applied immediately after planting with a small-plot sprayer mounted on a bicycle wheel applicator and pressurized with a CO2 canister. Liquids were applied in a 7-inch band over the row with a Teejet 8003E nozzle at 23 psi to deliver 10 gal/acre. A rake dragged lightly over the soil surface was used for incorporation. 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 directed the insecticide to both sides of the corn row directly in front of the cultivator sweeps. Liquid insecticides were applied just prior to cultivation with the small-plot bicycle sprayer. In mid July, rootworm feeding was evaluated by digging 5 roots from each treatment row and rating the 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). Chemical phytotoxicity was checked by taking stand counts from 1/1000 acre for each treatment and measuring the height of 10 consecutive plants from each treatment. Lodging counts were taken at harvest time. A plant was considered lodged if the angle between the plant and the ground was —45 degrees or less. Yield trials were machine harvested. Roots dug from the yield trials were taken from a 15-ft area at the end of each replication. This area was not included in the harvest sample. Data were analyzed by means of analysis of variance procedures. Economic damage was observed in all tests (check root rating >3.00). No phytotoxicity was noted with any of the insecticide treatments.