(F67) CORN (FIELD): Zea Mays L., 'Pioneer 3394' Western corn rootworm (WCR): Diabrotica virgifera virgifera LeConte R. R. Youngman Department of Entomology Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0319 Phone: (540) 231-9118 Fax: (540) 231-9131 Email:
[email protected], C. A. Laub Email:
[email protected], T. P. Kuhar Email:
[email protected], T. A. Dellinger Email:
[email protected], EFFICACY OF GRANULAR AND LIQUID INSECTICIDES AGAINST CORN ROOTWORM LARVAE, 1999: An experiment was conducted at the Virginia Tech Kentland Research Farm in Montgomery Co., VA, to determine the effectiveness of several granular and liquid insecticides, applied infurrow or T-band at planting, against WCR 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 a 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 device which 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 granules was inverted and placed in each of the wooden holders. This method helped minimize soil compaction because the tractor made only one 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 gal water/acre 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 infurrow tubes for the granular insecticides were replaced with the liquid delivery tubes. The roots of five consecutive corn plants were dug from each plot on 7 Jul and washed of excess soil before damage ratings were made. WCR damage ratings were based on the Iowa 1-6 scale (1=no feeding damage, 6=three or more root nodes completely destroyed). A two-way ANOVA and Fisher's protected LSD were used to analyze differences in root ratings among treatments. The treatment source of variation for root damage ratings was highly significant (P < 0.0001) according to ANOVA. The root ratings in the check plots averaged 5.20, which was significantly higher than the root ratings for all the insecticide treatments. Root ratings among the insecticide treatments ranged from a low 2.80 for Aztec 2.1G (T-band) and Force 3G (in-furrow) to a high of 3.35 for Regent 4SC (in-furrow). No insecticide phytotoxicity was observed in any plot.
