Insect screening results: multiple insect resistance in 59 commercial corn hybrids-2022

Authors: Ni, Xinzhi; TOEWS, MICHAEL - University Of Georgia; BUNTIN, G. DAVID - University Of Georgia

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 12/5/2022
Publication Date: 12/28/2023
Citation: Ni, X., Toews, M.D., Buntin, G. 2023. Insect screening results: multiple insect resistance in 59 commercial corn hybrids-2022. In: D.J. Mailhot, D. Dunn, and G. Ware (eds), Georgia 2022 Corn, Sorghum, and Summer Annual Forages Performance Tests. Georgia Agricultural Experiment Stations Annual Publication. pp. 24-27.

Interpretive Summary: not required.

Technical Abstract: Commercial corn hybrids were screened for ear- and kernel-feeding insect resistance under field conditions at Tifton, GA, and the results are summarized in the following table. A total of 59 transgenic Bt hybrids were included in this year’s trial; 12 hybrids were rated Very Good (VG), the highest rating for multiple insect resistance in 2021; 16 were Good (G); 14 were Fair (F), and 17 were Poor (P) as shown in Table 1. Of all 59 hybrids in this trial, seven have Roundup Ready trait (denoted by RR or GT in seed names), three have SmartStax™ (SS), two have YHR (also known as Optimum® Intrasect™), 26 have VT2P or VC trait (Genuity Viptera Double PRO®), four have TC or TRE (Trecepta Technology), and one has the VT2P trait with refuge in bag (RIB). RIB hybrids are a blend of 95% transgenic seeds with 5% non-transgenic seeds as a strategy for management of insect resistance to Bt genes. But regulations require that in cotton-growing areas, which includes Georgia, all Bt corn hybrids both pure Bt transgenic corn seed and the RIB products have a 20% non-Bt seed planting as a refuge. Please see the bag tag and seed dealers for details about the Bt corn refuge requirements. For all value-added traits in this report, RR or GT denotes for herbicide Roundup tolerant technology, and the SS traits combined multiple transgenic technologies to control both above- and below-ground insect pests, as well as for herbicide tolerance. The YHR traits include a combination of two insect protection traits – Herculex® I and YieldGard® Corn Borer. The VT2P or VC traits contain a stack of two Bt genes that target foliar- and ear-feeding lepidopteran pests. TC or TRE was built on the proven VT2P Technology, which gives extra control against corn borers and other above ground pests. Flowering time of all entries was between 53 and 60 days after a relatively late planting (April 23, 2022) due to precipitation in April. In comparison to 2021 (61-65 days after planting), the earlier flowering in 2022 reflected the relatively warmer weather conditions before pollination at the Tifton location. Because no trial was performed in 2020 due to the pandemic of COVID-19, the data from 2019 and 2021 were used for multiple year performance assessment in Table 1. Overall insect damage on corn ears in 2022 was relatively low when compared to the observed damage in 2019 and 2021. The six types of ear- and/or kernel-feeding insects in order of damage severity were: corn earworm and fall armyworm, stink bugs, the pink scavenger caterpillar, maize weevil, and sap beetles. Corn earworm and fall armyworm damage was measuring by the length (cm) of feeding damage penetrated from the tip of the ear toward the base. Feeding penetration by natural infestation of these lepidopteran pests (from the means of the five sampled ears per plot) was between 0 and 2.03 cm per ear, which was much less than the damage observed in 2021 (0-2.2 cm). Kernel-feeding insect damage was assessed by percentage (%) of damaged kernels per ear. The number of kernels per ear were estimated by multiplying the number of kernels per row by the number of rows from a representative ear for each plot. Because of kernel feeding insect damage was low, maize weevil, stink bug, sap beetle, and pink scavenger caterpillar damage was combined, which was ranged between 0.18-1.47% of the damaged kernels in 2022. The data related to insect damage were subjected to the principal component analysis using ear and kernel damage. In addition, corn rootworm and corn borer damage were not detected at the Tifton trial in 2022. Corn husk tightness and extension are considered important traits for ear- and kernel-feeding insect resistance, thus, husk features of the sampled ears were examined. Husk tightness was assigned using a scale of 1 to 5, in which 1 = very loose and 5 = very tight. Average ratings for husk tightne