Field Corn, Corn Rootworm Larval Control, 1982

Rootworm planting-time, soil-insecticide test plots were established at five Iowa locations in 1982. The experimental design for these tests was a randomized complete block with four replications for yield trials. The root-protection trials had 50-ft, single-row treatments and were planted at Atlantic, Nashua, Sutherland, Ames, and Earling on 30 Apr., 1 June, 4 May, 29 Apr. and 8 May, respectively. The yield trials had 50-ft, double-row treatments and were planted adjacent to the root-protection trials at Atlantic, Nashua, and Ames. Granular insecticide formulations were applied with modified Noble metering units that had been laboratory-calibrated to accurately deliver material at a tractor speed of 3 mph. Banded liquid formulations were applied with the self-contained small plot sprayer that had a Tee Jet 8003E nozzle using a pressure of 20 lb/in2. The applicators were mounted on a Model 71B, John Deere four-row unit planter. The 7-in. banded treatments were applied in front of the press wheels and incorporated with drag chains. Furrow treatments placed the insecticide directly in the seed furrow before it was closed. Rootworm feeding was evaluated by digging 5 roots from each treatment row and rating the damage on the Iowa 1 to 6 scale (1, equal to no feeding and 6 equal to 3 nodes of roots completely destroyed). Lodging counts were taken when the angle between a plant and the ground was 45 degrees or less. Yields were determined by machine harvesting 1/195 acre and converting the data to bu/acre of No.2 shelled corn at 15.5% moisture.