Evaluation of in-furrow applied insecticides for corn rootworm management near Colman, South Dakota, 2023

The corn rootworm (NCR/WCR) management efficacy trial was established on 9 May 2023 at the site near Colman, South Dakota. Experimental plots were arranged in a randomized complete block design with 4 replications. Each plot was 4 rows wide with 30-inch row spacing between rows and 48 feet in length. A non-rootworm traited seed corn hybrid Dekalb (DKC44-98RIB VT2P) was planted using an SRES Step 4 Planter with a seeding rate of 30,800 kernels per acre. The Aztec HC 2.1G and Force 6.5G insecticides were applied at planting using the SmartBox metering system. The SmartBox insecticide application meter was adapted to fit the Noble meter mounting brackets on the planter. At planting, in-furrow liquid insecticides were applied at 4 gallons per acre using a compressed air R&D sprayers system with solid stream spray tip sprayed into the open seed furrow after seed drop. Plant stand count (31 May) and lodging (15 Aug) data were collected from the center 2 rows of each plot. Stand was determined by counting the number of plants in 17.5 feet of row (1/1,000th of an acre) and percent lodging was calculated as the total number of plants in the rows that were at a 30-degree or greater angle then divided by total number of plants. Root rating means were derived from 6 roots dug randomly from the 2 outer rows at the VT growth stage on 20 July. Roots were washed and then rated for severity of rootworm feeding injury using the Oleson 0–3 root injury scale. Yield assessments in bushels per acre were taken from the center 2 rows of the 4 row plots on 18 Oct. Plant stand, root rating, lodged plants, and yield were analyzed using analysis of variance means separation according to Duncan’s new multiple range test in the ARM research management software.

Corn root injury in the untreated control was significantly worse than the insecticide treatments due to corn rootworm larval feeding and greatly exceeded the 0.25 economic injury level (EIL) (1.7) (Table 1). Capture LFR (0.49 fl oz/1,000/ft) had a rating of 0.28, but the other treatments had minimal root injury from larval feeding. The insecticide-treated plots in this study had 15–44.5% lodging. The Ethos Elite LFR was the only insecticide treatment that had a greater percentage of lodged plants when compared to the untreated control. However, it yielded 23.7 bushels/acre more than the untreated control and it had the 4th highest yield of any treatment. Numerically, the Force 6.5G insecticide had the least amount of rootworm injury (0.09) and the highest yield (172.5) when compared to the other treatments. The Ethos XB and Force EVO insecticide-treated plots had 3.3 and 4.3 lower yields than the untreated control. Although yield was not significant among the treatments, the other insecticide treatments exceeded the untreated control by 10.8–35 bushels acre.¹

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