In-furrow applied insecticides at planting time for corn rootworm management near Bryant, South Dakota, 2023 Open Access

A corn rootworm (NCR/WCR) management efficacy trial was established on 10 May 2023 at the site near Bryant, South Dakota. Four-row-wide experimental plots that were 48 feet in length with 30-inch row spacing were arranged in a randomized complete block design with 4 replications. Plots were planted using non-rootworm traited seed corn hybrid Northrup King (NK953-3220). Seed corn was planted at 30,800 kernels per acre at all locations. The Aztec HC 2.1G and Force 6.5G insecticides were applied at-planting time using the SmartBox metering system. The SmartBox insecticide application meter was adapted to fit the Noble meter mounting brackets on a 4-row SRES corn planter. At planting-time in furrow liquid insecticides were applied at 4 gallons per acre using a R & D sprayers system with solid stream spray tip sprayed into the open seed furrow after the seed drop. Plant stand counts (31 May) and lodging (12 Aug) data were collected from the center 2 rows of each plot at Bryant. 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 the total number of plants in the row divided by those that were at a 30-degree or greater angle. Root rating means were derived from 6 roots dug randomly from the 2 outer rows at growth stage VT on 25 Jul at Bryant. Roots were then washed and rated for severity of rootworm feeding injury using the Oleson 0–3 node injury scale (NIS) root injury scale. Yield assessments in bushels per acre were taken from the center 2 rows of the 4-row plots on 19 Oct at Bryant. 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 due to corn rootworm larval feeding greatly exceeded the 0.25 economic injury level (EIL) at Bryant (1.21) (Table 1). The Capture LFR at 0.49 fl oz/1,000 per row foot, index, and Ethos XB failed to prevent rootworm feeding from exceeding the 0.25EIL at Bryant location (0.29, 0.33, and 0.28). However, the feeding injury did not result in a significant increase in lodged plants or a decrease in yield when compared to the treatments with less than 0.25 NIS. The addition of an insecticide treatment resulted in a 12.7–42.3 of bu/acre less than the untreated plot in 2023 at this location.¹

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