Corn Rootworm Control, 1988

Abstract

Abstract Planting-time soil insecticide test plots were established at 6 Iowa locations in 1988. Two locations also were used for cultivation-time tests. The experimental design was a randomized complete block with 4 replicates for the root-protection trials (registered and experimental products) and 6 replicates for the yield trials (registered products only). All treatments were applied to 50-ft-long rows on 30-inch spacing. The root protection trials had single-row treatments; yield trials had double-row treatments. Granular insecticide formulations were applied with modified Noble metering units that had been calibrated to deliver material at 4 mph. The applicators were mounted on a 4-row John Deere Max-Emerge 7100 integral planter. Each row was monitored constantly to ensure that insecticide was being correctly applied at all times. Drag chains were 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 positioned directly in front of the cultivator sweeps directed the insecticide to both sides of the corn for basal treatments. Banders positioned directly above the plant whorl provided whorl treatments. The inclusion of soybeans in our trials resulted from grower testimonials reporting the prevention of rootworm damage by applying ground soybeans. Soybeans were gound to a size similar to that of insecticide granules and applied at 11.2 lb/acre, the highest rate possible. The low bulk density of soybean meal caused the drop tubes to clog at higher rates. In early Jul, 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 1/1,000 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° or less. Yield trials were machine harvested. Roots also were evaluated for larval damage in the yield trials by digging them from a 15-ft area at the end of each treatment. This area was not included in the harvest sample. Even though many parts of Iowa experienced drought conditions later in the growing season, there was sufficient moisture at all 6 locations following planting to establish good stands. At least 1/2 inch of rain fell at all locations within 2 wk after plot establishment. To determine treatment differences, data were subjected to ANOVA.