Abstract
Abstract An experiment was conducted in Orange County, Va., to determine the effectiveness of several commercial and experimental granular insecticides against corn rootworm larvae. The field used in this experiment has been in continuous corn for more than 20 years. The predominant soil type for this field is a Manassas silt loam, with some areas of Penn silt loam and Rapidan silt loam. The experimental design involved a randomized complete block wtih 4 replications. Plots were 30-ft long and consisted of 2 rows spaced 30 inches apart. A John Deere, 2-row Max-Emerge planter was used to plant all plots on 7 Jun at a plant population density of 26,000 plants/acre. Insecticide granules were applied in front of the press wheels either directly in the seed furrow or in a 5-inch T-band over the furrow, depending on the treatment. Prior to application, the regular granular insecticide applicators were removed from each side of the planter in order to accommodate 2 wooden boxes designed to hold inverted pint canning jars (Mason) for dispensing the insecticide granules. Attached to the underside of both wooden boxes was a plastic funnel and tube through which the insecticide granules flowed. A single opening, drilled into the lid of each jar, was laboratory-calibrated to deliver insecticides 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, 2 jars containing the appropriate insecticide granules were inverted and placed in the box holders. This method helped minimize soil compaction because the tractor made only 2 pass/plot. Stand counts were made on 29 Jun, by determining the number of corn plants in 3 separate, 3.3-row ft sections/ plot. The roots of 5 consecutive corn plants were dug from each plot on 19 Jul and washed of excess soil. Corn rootworm damage ratings were based on the Iowa 1-6 scale (1—no feeding; 6—3 or more root nodes completely destroyed).
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