Evaluation of Liquid and Granular Insecticide Formulations at Planting For Larval Corn Rootworm Control, 2018B

The objective of the study was to evaluate the effectiveness of liquid and granular insecticide formulations applied at planting for larval WCR control under irrigated, continuous corn production. ‘DeKalb DKC64-35RIB’ (contains VT Double PRO RIB traits for above-ground insects) corn hybrid was planted using 35,700 seeds/acre on 1 May 2018 at the South Central Agricultural Laboratory near Harvard, NE. The corn hybrid received a seed-applied insecticide treatment of clothianidin at 0.25 mg AI/seed. During 2017 the trial site was planted to corn (late-planted) and pumpkin (insecticide free). The experimental design was an RCB with four replicates. Plot size was 4 rows × 68–72 ft length with 30-inch row spacing. Row length of each plot was measured and used for plant density and yield calculations. Soil type was a Crete silt loam. Insecticide compounds, formulations, and application rates are provided in Table 1. All plots, with exception of one set of plots that was treated with Force 3G (two Force 3G treatments, with and without starter fertilizer), received 5 gal per acre of 10-34-0 starter fertilizer at planting. Liquid insecticide treatments were mixed and applied with the starter fertilizer. Starter fertilizer and starter fertilizer–liquid insecticide mixtures were applied in-furrow (IF) with a compressed air system at 5 gpa. Granular insecticide formulations were applied IF via SmartBox application system. Plant density was determined on 22 May. The total number of plants in the center two rows of each plot was counted and converted to plants per acre (PPA). Initial WCR egg hatch was first documented on 29 May. Extended leaf height (ELH) of 20 randomly selected plants in the center two rows of each plot was recorded in inches on 14 Jun. Initial adult WCR emergence was observed on 25 Jun. The total number of root lodged plants in the center two rows of each plot due to larval WCR feeding was recorded on 29 Jun and converted to percent root lodged plants. A plant was considered to be root lodged if it was leaning ≥45° from vertical. Larval feeding damage was evaluated on 9 Jul. Five randomly selected plants were dug from each plot (three from row 1 and two from row 4), washed, and rated for corn rootworm injury using the 0–3 node injury scale (0 = no feeding, 1 = one node of roots pruned to within 1.5 inches of the stalk, 2 = two nodes of roots pruned to within 1.5 inches of the stalk, 3 = 3 or more nodes of roots pruned to within 1.5 inches of the stalk). From planting (1 May) to larval feeding damage evaluation (9 Jul), rainfall totaled 8.87 inches and overhead irrigation, 1.10 inches. The center two rows of each plot were machine harvested on 18 Oct. Percent moisture and lbs of grain were recorded and corrected to 56 lbs/bu at 15.5% moisture to evaluate yield. Data were analyzed by PROC MIXED with mean separation using differences of least square means (P = 0.05).

Mean root injury ratings (0–3 scale) for the untreated check averaged 1.42 (Table 1). With exception of Capture LFR, all of the insecticide treatments applied at planting significantly reduced root injury levels and enhanced final grain yields compared with the untreated check. The use of liquid fertilizer with Force 3G had no significant effect on any of the variables measured. Furthermore, all of the insecticide treatments significantly reduced root lodging compared with the untreated check. There were no significant differences among treatments for extended leaf height or plant density.

This research was supported by industry gifts of pesticide and research funding.