Evaluation of Labelled and Experimental Insecticides for Control of Larval Corn Rootworm, 1996

Abstract

Abstract Planting and first-cultivation time insecticide trials were conducted at Clay Center, NE, to evaluate their effectiveness for larval corn rootworm control. Local population consisted of >95% WCR and <5% NCR. All plots were insecticide free from 1993-95. In 1995, plots were planted in trap crop. In 1992, Force 1.5G at 1.2 lb (AI)/acre was applied to all plots. Lorsban 15G at 1.21b (AI)/acre was applied to all plots in 1990 and 1991. The experimental design was a RCB with four replicates. Each treatment replicate consisted of a single row 30 ft long with a 30-inch row spacing. Soil type was a Crete silt loam with a 0-1% slope. All plots were planted on 21 May. Soil temperature at 2 inches was 78° F. Soil moisture at 0-2 inches was 13.2% and 16.5% at 2—4 inches using the gravimetric method. Granular insecticides were applied using 10 inch Almaco smooth belt cones mounted in place of insecticide boxes on a 2-row John Deere 7100 plateless planter. Preweighted amounts of insecticide granules were distributed uniformly around the belt cone by a divider funnel and either directed into the open seed furrow (IF) or a 7-inch band in front of the press wheel and over the open seed furrow and incorporated with a drag rake (TB). A CO2 pressurized backpack sprayer mounted on the planter was used to apply liquid insecticides. A TeeJet #250017 nozzle positioned between the disc openers was used to direct an in-furrow spray of 1.5 gpa at 14.5 psi (LP). On 10 Jun, initial corn rootworm egg hatch was detected and stand counts were taken. First-cultivation time treatments were applied on 17 Jun. Soil temperature at 2 inches was 76-78° F. A mason jar with holes in the lid was used to apply granular insecticides at first-cultivation. Granules were applied basally by shaking the mason jar and immediately incorporated with a garden rake (GC). A CO2 pressurized backpack sprayer with an output of 20 gpa at 30 psi was used to apply liquid insecticides at first-cultivation. Liquid insecticides were broadcast over the top of the plant whorl and insecticide reaching the soil surface was immediately incorporated with a garden rake (LC). Plots were cultivated on 20 Jun. Larval feeding damage was evaluated on 16-17 Jul. Five plants were dug from each treatment replicate and rated using the Iowa 1-6 scale (1, no feeding, to 6, 3 or more nodes of roots completely destroyed). Data were analyzed by ANOVA for RCB with mean separation using DMRT.