Efficacy of Soil Insecticides Against Western Corn Rootworm, 1993
Authors: Youngman R. R. , Kuhar T. P. , Laub C. A. , Nixon K. H. 
Published: December 2017

An experiment was conducted in Augusta Co., VA, to determine the effectiveness of several experimental and commercial granular insecticides applied in-furrow or T-band, as well as in-furrow application of an experimental liquid insecticide, against western corn rootworm larvae. The experiment was conducted near the center of a no-till cornfield consisting of a predominant Frederickson clay loam soil. The field had been in continuous corn production since 1988. Also, no granular insecticides had been applied to the field at planting since 1988. Plots of 40 × 5 ft (2 rows wide) were arranged in a RCBD with all insecticide treatments and an untreated check replicated 4 times. An Almaco, 2-row Max-Emerge planter was used to plant the plots on 28 May at a population density of 26,100 seeds/acre. Insecticide granules were applied in front of the press wheels either directly in the seed furrow or in a 5-inch wide T-band over the furrow, depending on the treatment. The regular 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 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, 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 1 pass per plot. The experimental liquid insecticide, TD 2328 (diazinon), was applied directly in-furrow at 2 rates: 0.49 lb (AI)/acre and 0.73 lb (AI)/acre using a backpack sprayer. The sprayer setup involved a 2-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 lubes for the granular insecticides were replaced with the liquid delivery tubes. Both rates of the liquid insecticide treatments were applied using 20 gal water/acre at 40 psi. Root ratings and stand counts were made in all plots on 10 Jul. The roots of 5 consecutive corn plants were dug from each plot and washed of excess soil before ratings were made. Corn rootworm damage ratings were based on the Iowa 1-6 scale (1 = no feeding damage; 6 = 3 or more root nodes completely destroyed). Stand counts consisted of counting all of the cornstalks along a 20 row-ft section in each plot. The treatment plots were hand-harvested on 14 Sep by cutting all cornstalks from two, 16.4 row-ft sections per plot. All stalks were cut within 1 to 2 inches above the soil surface and then weighed in the field using a milk scale to determine the wet weight at harvest. Immediately after a sample was weighed, 10 cut stalks were removed from the pile and chopped into 2- to 3-inch pieces using a Troy-Bilt® Tomahawk® Chipper/Shredder. A 2.2-lb subsample of shredded material was removed from each plot and dried at 130 to 140°F for 48 h at the VPI&SU Agronomy Farm. A 2-way ANOVA with Fisher’s protected LSD was used to analyze differences among treatments.