Field Corn, Corn Rootworm Larval Control, 1985

Soil insecticide trials at planting time and first cultivation were conducted at Mead, Neb., for corn rootworm control. The test plots were in trap crop during 1984 (no insecticide) and had been used periodically for multiclass insecticide trials for at least 10 yr prior to 1983. The soil type was a silty clay loam. The experimental design for each test was a randomized complete block with 4 replications. Each replication consisted of single-row treatments that were 35 ft long and 30 inches apart. Planting-time application equipment consisted of modified V-belt seeders mounted on a model 80 John Deere—flex planter. Preweighed amounts of insecticide granules were placed on the V-belts and directed into seed furrow or banded over the row in front of the press wheel. Noble—granular insecticide metering units mounted on a hand-powered bicycle ipplicator were used to apply soil insecticides at first cultivation. Granules were banded directly over the plant whorl and then immediately incorporated by ihe cultivator. Corn was planted 6 May, and first-cultivation treatments were applied 6 Jun. Soil moisture conditions were excellent when insecticides were lpplied. Initial corn rootworm egg hatch was detected 24 May. Stand counts were taken on 30 May and 15 Oct in all plots. Plant evaluations were made on SO May in planting-time tests to determine whether any insecticide treatments adversely affected corn development. Plants were considered abnormal if :hey were stunted or exhibited deformed growth patterns (i.e., buggy whipping). Feeding damage was evaluated (8 to 11 Jul) by digging 5 roots from each ireatment row and rating the damage by means of the Iowa 1-6 scale (1, no feeding, to 6, 3 or more nodes of roots completely destroyed). Lodging counts vere taken in October. A plant was recorded as lodged if the angle between the soil surface and the plant stem was ≤67.5 degrees. Data were subjected to in analysis of variance, and an LSD test was used for mean separation where statistical differences occurred