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

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. ‘Pioneer P1151AM’ (contains Optimum AcreMax Insect Protection System for above-ground insects) corn hybrid was planted on 1 May 2018 at the South Central Agricultural Laboratory near Harvard, NE. The corn hybrid received Pioneer Premium Seed Treatment 250 (seed-applied insecticide treatment of Cruiser 250 [0.25 mg ai/seed of thiamethoxam] and Lumivia [0.25 mg ai/seed of chlorantraniliprole]). 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. Soil type was a Crete silt loam. Insecticide compounds, formulations, and application rates are provided in Table 1. 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 23 May. The total number of plants on 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 lodge plants. A plant was considered to be root lodged if it was leaning ≥45° from vertical. Larval feeding damage was evaluated on 10 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 (10 Jul), rainfall totaled 8.87 inches and overhead irrigation, 1.10 inches. The center two rows of each plot were machine harvested on 4 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 1.64 (Table 1). All insecticides significantly reduced larval WCR root injury ratings and early season root lodging compared with the untreated check. There were no significant differences among treatments for extended leaf height, plant density, or yield.

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