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

A corn rootworm (NCR/WCR) management efficacy trial was established on 16 May 2023 at the site near Cavour, South Dakota. Experimental plots were arranged in an RCBD with 4 replications. Plots were 4 rows wide and 48 feet in length with 30-inch row spacing. Plots were planted using a Pioneer corn hybrid (9624AM) without rootworm traits. Seeds were planted using an SRES Step 4 Planter with a seeding rate of 30,800 seeds per acre. 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 the planter. In-furrow liquid insecticides were also applied at planting with a rate of 4 gallons per acre using a compressed air R&D sprayers system with a solid stream spray tip sprayed into the open seed furrow after the seed drop. Plant stand counts (1 June) and lodging (17 September) 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). Percent lodging was determined by counting the total number of plants in the rows that were at a 30-degree or greater angle and then dividing by the total number of plants in the row. Root rating means were derived from 6 roots that were dug randomly from the 2 outer rows at growth stage VT on 18 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 23 October. 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. The UTC had corn rootworm feeding injury that greatly exceeded the 0.25 economic injury level (EIL) at 1.57 (Table 1). The Capture LFR (0.98 and 0.49 fl oz/1,000 row-ft) and Ethos Elite LFR exceeded the 0.25 EIL by 1.24, 1.56, and 1.48 times (Table 1). The Capture LFR (0.49 fl oz/1,000 row ft), Ethos XB, and Ethos Elite LFR treatments yielded significantly better than the Aztec HC, MBI-306, and Xpedient Plus treatments. Aztec HC, MBI-306, and Xpedient Plus had numerically lower yield than the untreated check plots (1.2, 1.1, and 1.17 times lower). During 2023 at the site near Cavour, the rootworm feeding injury that exceeded the 0.25 root injury rating did not necessarily result in decreased yield, and in some cases treatments with higher root injury yielded greater than those with lower ratings. This suggests that other biotic or abiotic factors may have influenced yield.¹

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