EFFICACY OF GRANULAR AND LIQUID INSECTICIDES AGAINST CORN ROOTWORM LARVAE, 2000

Abstract

An experiment was conducted at the Virginia Tech Kentland Research Farm in Montgomery County, VA, to determine the effectiveness of several granular and liquid insecticides, applied in-furrow or T-band at planting, against western corn rootworm larvae on Pioneer variety ‘3394’ corn. The experiment was conducted in a 5-acre, continuous cornfield with a McGary and Purdy dark gray silt loam soil type. Plots of 30 x 10 ft (four rows wide) were arranged in an RCBD, with all insecticide treatments and an untreated check replicated four times. An Almaco, 2-row Max-Emerge planter was used to plant the plots on 12 May at the rate of 28,000 seeds/acre on 30-inch rows. Insecticide granules were applied in front of the presswheels either directly in the seed furrow or in a 5-inch wide T-band over the furrow, depending on the treatment. The standard granular insecticide applicator was removed from each row unit and replaced with a wooden holder that held an inverted pint canning jar (Mason) used to dispense the insecticide granules. Attached to the underside of the wooden holder was a plastic funnel and tube through which the insecticide granules flowed. A single opening, drilled into the lid of each jar, was calibrated in the laboratory to deliver insecticide granules accurately at a speed of 3 mph. The possibility of mixing one or more insecticides was avoided by using a separate jar and lid for each treatment. At the start of application, a jar containing the appropriate insecticide was inverted and placed in each of the wooden holders. This method helped minimize soil compaction because the tractor made only one up and back pass per plot. The liquid insecticide Regent 4SC was applied in-furrow at a rate of 0.13 lb (AI)/acre using a backpack sprayer calibrated to deliver 20 gpa at 40 psi. The sprayer setup involved a two-nozzle spray boom with each nozzle inserted into its own clear plastic delivery tube. Immediately before application of the liquid insecticide, the regular in-furrow tubes for the granular insecticides were replaced with the liquid delivery tubes. The roots of ten consecutive corn plants, five from each of the center two rows, were dug from each plot on 11 Jul and washed of excess soil before damage ratings were made. Corn rootworm damage ratings were based on the Iowa 1–6 scale (1 = no feeding damage, 6 = three or more root nodes completely destroyed). Stand counts were determined in each plot on 17 Jul by counting the number of stalks per 20 row-ft. A two-way ANOVA and Fisher’s protected LSD were used to analyze differences among treatments in root damage ratings and stand counts.