Protecting Yield Potential: How Bt Hybrid Corn is performing in South Carolina

Bt corn remains one of the most effective tools for managing key insect pests like corn earworm and fall armyworm. However, shifting pest pressure and resistance to some Bt toxins make it critical to continuously validate performance under South Carolina conditions.

Insect pressure—particularly from corn earworm and fall armyworm—continues to evolve, with increasing evidence of reduced susceptibility to Bt traits. As resistance develops, hybrid performance becomes more variable, making local data essential for hybrid selection and insect management strategies. This project provides growers with region-specific performance data to guide seed decisions and protect yield potential.

Fall armyworm

Corn earworm

Methods

Field trials were conducted at Pee Dee REC (Florence) and Edisto REC (Blackville) using replicated plots of Bt and non-Bt hybrid corn. Hybrids evaluated included:

• Dekalb: non-Bt, VT2P (Cry1A.105 + Cry2Ab2), and and Trecepta (Cry1A.105 + Cry2Ab2 + Vip3A)

• Pioneer: non-Bt, Optimum Intrasect (Cry1Ab + Cry1F), and Optimum Leptra (Cry1Ab +

• Cry1F + Vip3A)

Trials were planted at an early planting window (April) and a kate planting window (June).

Unique to this study was the measurement of corn earworm pupal weight, providing insight into sub-lethal effects of Bt toxins and potential resistance development.

Fall armyworm larvae and injury on corn planted at Edisto REC in Blackville, SC. Photo credit: Francis Reay-Jones

Results

While final results are still being compiled, the study is designed to:

• Quantify differences in insect injury across trait packages

• Evaluate whether Bt hybrids still suppress larval survival

• Determine yield advantages under different planting dates and pest pressures

Preliminary observations suggest that sub-lethal effects (e.g., reduced pupal weight) may be diminishing, indicating possible resistance trends—an important signal for long-term trait durability. 

Data collection included:

• Stand counts (V4)

• Fall armyworm injury ratings (V8)

• Corn earworm injury (kernel area damaged)

• Corn earworm pupae collection and weight (to assess survival and sub-lethal effects)

• Final grain yield

The next steps for this trial will be to finalize yield and injury data across all locations, deliver hybrid-specific recommendations prior to 2027 seed purchasing decisions, and integrate findings into broader insect management strategies, including UAV-based spraying for stink bugs.

For growers, this work reinforces that trait selection alone is no longer sufficient—hybrid choice must be paired with active pest management.

This information is from the 2025 research project, Simulating Defoliator Injury Thresholds, Stem-Feeder Injury Thresholds, and Natural Pest Population Thresholds. The lead was University of Clemson researcher Dr. Jeremy Greene. Project sponsored by the South Carolina Corn Board.