Corn rootworm management with in-furrow applied insecticides near Cavour, South Dakota, 2024

A general corn rootworm (NCR/WCR) management efficacy trial using registered insecticides was established on 15 May 2024 at the site near Cavour, South Dakota. Experimental plots were arranged in an RCBD with 4 replications. Each plot was 4 rows wide and 46 feet in length with 30-inch row spacing. Pioneer corn hybrid (9193AM) without rootworm traits seeds were planted using an SRES Step 4 Planter with a seeding rate of 30,800 seeds per acre. The AztecHC 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. Liquid insecticides were applied in-furrow at planting with water as a carrier at 5 gallons per acre. Liquid insecticides were applied using a compressed air R&D sprayers system with solid stream spray tip applied into the open seed furrow after seed drop. Plant stand count (4 Jun) and lodging (14 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). 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 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 16 Jul. Roots were washed and then rated for severity of rootworm feeding injury using the Oleson 0 to 3 root injury scale. Yield assessments in bushels per acre were taken from the center 2 rows of the 4 row plots on 22 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.

The untreated check (UTC) had corn rootworm feeding injury that greatly exceeded the 0.25 economic injury level (EIL) with a rating of 1.9 nodes of injury, 7.6-fold above the EIL (Table 1). All of the insecticidal treatments had significantly less root injury when compared to the untreated. However, the Capture LFR (8.5 oz/acre) treatment nearly exceeded the 0.25 EIL with a rating of 0.24 (Table 1). At this location, there were no significant differences among treatments for plant stand density or lodged plants (Table 1). The high rootworm feeding pressure in the untreated plots did not result in significantly reduced yield when compared to the insecticide treatments. This could be due to adequate rainfall and no wind events that would have increased the number of lodged plants. Although not significant, the Elevest and F4260-1 treatments yielded more than 20 bu/acre more than the untreated control.¹

Footnotes