Evaluation of Seed-Applied and Liquid and Granular Insecticide Formulations at Planting For Larval Corn Rootworm Control, 2018 Open Access

The objective of the study was to evaluate the effectiveness of seed-applied, liquid, and granular insecticide formulations applied at planting for larval WCR control under irrigated, continuous corn production. ‘Munson 6699VT2P RIB’ (contains VT Double Pro RIB Complete Corn Blend traits for above-ground insects) corn hybrid was planted at 32,100 seeds per acre on 30 Apr 2018 at the South Central Agricultural Laboratory near Harvard, NE. 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 × 69–75 ft length with 30-inch row spacing. Row length of each plot was determined 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. The corn hybrid seed received either a seed-applied insecticide treatment of Poncho 500 (clothianidin at 0.5 mg AI/seed), Poncho 1250 (clothianidin at 1.25 mg AI/seed), or left untreated. Seed-applied insecticides (SAI) were applied to seed commercially. Plots that received and in-furrow insecticide treatment (liquid or granular) were planted with seed that did not receive an insecticide seed treatment. Liquid insecticide formulations were applied IF in a 5 gpa water solution via compressed air system. Granular insecticide formulations were applied IF via SmartBox application system. Plant density was determined on 21 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 (30 Apr) 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 20 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 node injury scale) for the untreated check averaged 1.09 (Table 1). Only Aztec and Force significantly reduced larval WCR root injury ratings compared with the untreated check. All liquid and granular insecticides applied at planting-time significantly reduced percent root lodged plants compared with the untreated check. Seed applied insecticides did not reduce root injury of percent root lodged plants compared with the untreated check. Only Ampex (both rates) and Aztec resulted in significantly higher yields 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.