Corn Rootworm Larval Control with Counter in 15- and 30-Inch Row Centers, 1997

This experiment was designed to test the efficacy of Counter 20 CR in 15- and 30-inch row centers at both full and half labeled rates. The experimental design was a split plot with four replications. Row center was the whole-plot treatment and insecticide was the subplot. The test was planned as conventional-till on 5 May into an area that had been planted to a rootworm trap crop the previous year (silty loam soil type). Treatments in the 3-inch row centers consisted of four rows 10 ft wide by 30 ft long. Treatments in the 15-inch row centers consisted of eight rows (10 ft wide) by 30 ft in length. Fifteen-inch row centers were accomplished by splitting the 30-inch centers with a second pass of the planter. Granular insecticide formulations were applied with modified Noble meter-ing units mounted on a 4-row John Deere 7100 planter (30-inch row centers). Seeding rate was 26,100/acre for 30-inch centers and 33,200 for 15-inch centers (16,600 each pass). The Noble insecticide metering units were field calibrated at both seeding rates and set accordingly. Insecticide was applied at the same oz (AI)/1000 row-ft rate, for each row-center treatment, regardless of seeding rate. Rootworm larval feeding was evaluated on 15 Jul by digging 3 roots from the center two rows of each treatment 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). Lodging counts were taken on 22 Oct. A plant was considered lodged if the angle between the base of the plant and the ground was 45° or less. ANOVA was used to examine treatment main effects and interactions with row spacing. Means were separated with Ryan’s Q test (REGWQ).