Efficacy and Yield of Null and CRW Traited Hybrids With and Without Insecticides for CRW Control, 2017

Corn rootworm (NCR/WCR) management efficacy trials were conducted in 2016 to evaluate insect-resistant hybrids and granular insecticide combination treatments near Cavour, and Colman, South Dakota. The experimental plot was arranged in an RCBD with four ~50-ft-long replications. Treatments were established at planting time using four rows spaced 30 inches apart. Each hybrid tested was planted with no insecticide as well as with Aztec and Index. Granular Aztec HC insecticide was applied with the SmartBox delivery system. SmartBox meters were adapted to fit small bottles and a plate was attached to the bottom side of unit to fit in Noble meter mounting brackets on a 4-row Kinze corn planter. The SmartBox meters and liquid application equipment were calibrated before treatment application. In-furrow treatments were placed directly into the open seed furrow between double-disk openers. The trial was conducted within two corn germlasm groups (Dekalb and Pioneer). The Dekalb hybrid group evaluated consisted of 1) VT Double PRO RIB Complete ‘DKC45-66RIB (VT2P)’ (check with no CRW Bt) and 2) SmartStax RIB Complete (SS), Monsanto/DeKalb ‘45-65RIB’. The pioneer hybrid group consisted of 3) Pioneer Optimum AcreMax Xtra (AMX) ‘P9526AMX’ and 4) Pioneer Optimum AcreMax XTreme (AMXT)’P926AMXT. The Pioneer AMX hybrid uses a single mode of action and the AMXT has two modes of action against rootworm larvae. Corn seed was planted at a rate of ~ 31,000 kernels per acre. Six roots per replication were randomly dug from the two outer rows, washed, and rated using the Iowa 0 to 3 root injury rating scale. A combine was used to harvest the center two rows of each plot for a yield assessment. Data were analyzed using PROC MIXED/PDIFF in SAS version 9.2 option with Saxton’s lettering macro (Table 1).

Corn rootworm feeding damage to roots of untreated VT2P corn exceeded the 0.25 EIL at Colman (1.60) and Bryant (1.71) sites. When Aztec HC was applied to these non-CRW hybrids, damage to the roots was significantly reduced from over 1.5 nodes of injury to 0.08 at both Colman and Bryant. No significant yield differences were measured at either location. Even with a moderately heavy rootworm feeding injury scores (1.6 and 1.71) associated with the check treatment (VT2P), the number of bushels per acre was not significantly reduced at either location in 2017 compared with the same treatment where root injury and lodging was largely managed by use of an insecticide application.

A portion of this research was supported by industry gifts.