Maximizing Corn Yields: Bt vs Non-Bt Hybrids in Statewide Large-Plot Trials

By Dominic Reisig

Bt corn growers are required to plant 20% of their total corn acres to non-Bt corn for resistance management. An important question is do growers lose yield on the 20% of the acres they plant to non-Bt corn? In addition, recent economic analysis from Georgia indicated that growers pay an average of $14 to 28 more for Bt hybrids than non-Bt hybrids. If growers lose yield planting non-Bt corn will the seed savings offset potential losses?

Previous work in the state has focused on small-plots comparing non-Bt hybrids and Bt hybrids at the Tidewater Research station in Plymouth, at research stations in North Carolina, South Carolina and Georgia (results published soon!), and in the OVTs. Across these trials we found that timely planted Bt and non-Bt hybrids from similar genetic backgrounds yield the same. In contrast there is a slight yield penalty to planting a non-Bt corn hybrid when it is planted beyond the last recommended planting date.

Therefore, according to data from 3 sets of multi-year experiments, growers who select a high-yielding non-Bt hybrid and plant it on time, will not lose yield compared to if they planted a Bt hybrid. But what if we put this into the hands of growers? How would non-Bt hybrids stack up?

Graduate student Alexis Alsdorf, recently collaborated with NCCE county agents across the state to test the efficacy and yield of non-Bt hybrids and Bt hybrids in large plot trials. We chose a non-Bt and Bt hybrid pair from both Dekalb and Pioneer. These were planted, maintained, and harvested on grower farms using grower equipment during 2022 and 2023 in 55 total fields spread across North Carolina from the mountains to the sea.

Bt hybrid efficacy was as expected. Feeding was mainly by corn earworm and was equal between both years. The hybrid expressing Cry and Vip Bt traits (DKC65-99) had very little feeding by corn earworm, the hybrid expressing Cry Bt traits (P1197YHR) and its’ non-Bt pair (P1197LR) had moderate feeding, while the non-Bt hybrid DKC67-70 had the most feeding. Note that corn earworm is resistant to the Cry Bt traits.

However, yields did not follow feeding patterns. Results were different between years, with yields tending to be higher in 2023. Importantly, yields were equal between non-Bt and Bt hybrid pairs in each year. DKC65-99 and DKC67-70 yielded the same in both 2023 and 2022. Similarly, P1197YHR and P1197LR yielded the same in both 2023 and 2022.

This matched the results from the 3 sets of multi-year experiments in small plots. Growers who select a high-yielding non-Bt hybrid and plant it on time, will not lose yield compared to if they planted a Bt hybrid. In fact, they could save on seed costs on the 20% of acres they planted to non-Bt.

We encourage growers to work with their corn seed provider to select appropriate high-yielding non-Bt hybrids for their 20% refuge acres.