Rootworm larval management using traited corn hybrids near Colman, SD, 2023

Corn rootworm (NCR/WCR) management efficacy trials were established on 9 May 2023 at Colman site in South Dakota. Experimental plots were arranged in an RCBD with 4 replications, with each plot being 48 feet in length and 4 rows wide with 30-inch row spacing. Plots were planted using an SRES Step 4 Planter with a seeding rate of 30,800 seeds per acre. For this experiment, we used non-rootworm-resistant seed corn hybrids (Dekalb [DKC50-88RIB: VT2Pro (VT2P)]; Channel [196-71VT2PRIB: VT2Pro (VT2P)]), and the following corn rootworm-traited hybrids: (Dekalb [DKC50-87RIB: SmartStax (SSRIB)]; Channel [199-11SxtRIB: SmartStax (SSRIB)]; Dekalb [DKC101-33RIB: SmartStax Pro w/ RNAi Technology (SSPRIB)]; Channel [198-82SSPRIB: SmartStax Pro w/ RNAi Technology (SSPRIB)]; Dekalb [DKC101-33RIB: VT4PRO (VT4PRIB)]; Channel [200-40VT4PRIB: VT4PRO (VT4PRIB)]) (Table 1). Plant stand counts (1 Jun) and lodging (17 Sept) 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 by counting the total number of plants in the row that were at a 30-degree or greater angle and then dividing that by total number of plants in the row. Root rating means were derived from 6 roots dug randomly from the 2 outer rows at growth stage VT on 18 Jul. Roots were washed and then rated for severity of rootworm feeding injury using the Oleson Root Injury scale of 0–3. The Oleson Root Injury scale is based on the proportion of nodal roots pruned to 1.5 inches or less. Yield assessments in bushels per acre were taken from the center 2 rows of each plot on 23 Oct. Plant stand, root rating, lodged plants, and yield were analyzed using ANOVA and means separation according to Duncan’s new multiple range test in the ARM research management software.

Corn root injury from rootworm feeding in the Dekalb and Channel untreated checks (VT2PRIB) exceeded the ~0.25 EIL at Colman (Table 2), with 1.25 and 1.56 nodes of root injury, respectively. The Dekalb and Channel seeds rootworm-traited hybrids (SSRIB, SSPRIB, and VT4PRIB) had a rating of 0.06–0.20. The Dekalb SSRIB hybrid was the only rootworm-traited hybrid that had 0.20 nodes of injury, which is near the 0.25 EIL. Sever pruning from rootworm larvae occurred on the SSRIB, but most of the roots were not pruned to 1.5 inches or less. Both SSPRIB and VT4PRIB had some larval feeding to roots that was over 1.5 inches; therefore, it could not be included as feeding injury. The Dekalb SSRIB had a 2% increased bu/acre compared with the untreated. This was the only hybrid tested with a yield above the non-rootworm VT2PRIB hybrid. There was no significant lodging of corn plants in the plot from rootworm feeding. Overall, the corn rootworm-traited hybrids were not significantly damaged by rootworm larvae. The 1.25 nodes of injury on the VT2PRIB Dekalb hybrid did not contribute to a significant number of lodged plants or decreased yield. However, the Channel seed non-rootworm-traited hybrid (VT2PRIB) had a significantly lower number of bu/acre harvested (28%, 17%, and 22%) compared to SSRIB, SSPRIB, and VT4PRIB hybrids. These rootworm-resistant hybrids are still an effective tool for managing corn rootworm larval feeding in South Dakota at the field site near Colman, SD.¹

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