The European corn borer (Ostrinia nubilalis) is a primary target of Bt corn. A study in North Carolina finds many growers of Bt corn aren’t planting refuge crops, a key strategy in slowing the corn borer’s development of resistance to insecticidal protein found in Bt crops. (Photo credit: Adam Sisson, Iowa State University, Bugwood.org)

By Josh Lancette

A new study from North Carolina found that corn growers in the state are not planting as much refuge crop as needed, potentially leading to increased insect resistance to Bt corn. Published in March in the Journal of Integrated Pest Management, the study also found that current methods for extension professionals to reach out to growers might not be working as well as hoped.

Josh Lancette

Bt crops are plants that have been genetically modified to express a protein produced by the bacterium Bacillus thuringiensis that is toxic to some insect pests when ingested. While Bt crops can be effective resources in an integrated pest management plan, one risk of Bt crops is that insect populations can grow resistant to them if effective management strategies are not used. One popular tactic to prevent insects from becoming resistant to Bt crops is to plant a “refuge” non-Bt crop next to the main Bt crop. The idea is that the refuge crop produces non-resistant insects, which then mate with any resistant insects in the main crop, producing mostly non-resistant offspring. Using a refuge crop is recommended for most Bt crops, with the one exception being Bt corn—the EPA has required growers of Bt corn to use a refuge crop since 2000.

However, in North Carolina, a survey indicated that growers of Bt corn aren’t living up to expectations in regard to refuge crops.

The survey was conducted by Dominic Reisig, Ph.D., an assistant professor at North Carolina State University. In the survey, approximately 300 growers in 16 North Carolina counties in 2014 and about 400 growers from 30 counties in 2016 were asked whether they plan to plant a refuge crop with their Bt corn. The results showed that only 38 percent to 44 percent of growers planned to plant a refuge crop alongside their Bt corn. Of the remaining growers, 22 percent to 29 percent were uncertain about whether they were going to plant a refuge crop.

Interestingly, even though many growers did not plan to plant a refuge crop, a majority of growers understood the importance of refuge crops and even considered it necessary.

Why the discrepancy? The answers aren’t clear, but Reisig has a few suggestions.

“Some of the resistance to planting refuge may be due to a lack of understanding about how important refuge crops are,” said Reisig in a press release. “But it’s also likely to be a function of the fact that many of the farms in counties with low refuge crop compliance are smaller operations. Growers may simply be trying to get more crop yield from their acreage—though there is little evidence of short-term benefit and ample evidence of long-term risk from Bt-resistant pests.”

Supporting the theory that not planting a refuge isn’t due to a lack of knowledge only, in 2014 Reisig gave two surveys, one before a presentation on the logic and necessity of refuge crops and one after, and found that while understanding of Bt crops increased because of the presentation, the number of growers who planned to plant a refuge did not. Furthermore, the increased understanding disappeared in the survey given in 2016 (which was given without a presentation).

“While I could boost grower knowledge in the short term using the oral presentation, this knowledge was gone two years later,” says Reisig. “Growers did not indicate that they would plant more non-Bt refuge after the presentation or two years later. Also, while growers are educated on planting non-Bt refuge by mailings, billboards, information on the maize seed bags, et cetera, by the seed industry, refuge plantings have been steadily decreasing over time. So, new and creative extension methods are needed beyond teaching about refuge using verbal presentations in county meetings.”

While Reisig is unsure of what those new methods are, he does have a couple suggestions for increasing grower compliance with refuge crop laws and recommendations.

“First, growers from areas with less intensive plantings of field crops tend to plant less non-Bt refuge,” says Reisig. “So, they could be targeted to increase compliance. Secondly, I also surveyed growers concerning some actions that could be done to increase refuge. Out of four options, two actions focused on financial incentives were popular, while two actions focused on punishment for noncompliance were not. So, we could incentivize growers to plant refuge.”

“I would like to work with industry to develop ways to partner to increase refuge compliance. I would also like to work with social scientists that may have some ideas on this subject. Too often in extension, we focus on giving out information, hoping to change practices. This was not successful in my study, and I don’t know how to do it at this point!”

Josh Lancette is manager of publications at the Entomological Society of America.