Refuge is not optional when it comes to Bt corn
In the scurry of planting season, cleaning out the planter to put in a 20% refuge can seem like a hassle. Failure to comply with refuge standards is not only illegal according to Environmental Protection Agency (EPA) guidelines, but it also puts technology at risk. Target insect pests have the opportunity to build resistance faster as use of Bt technology increases. If farmers don’t abide by refuge requirements, the possibility of developing resistance only heightens.
“I think of resistance as an arms race of us against the insects,” says Moneen Jones, assistant research professor at the University of Missouri.
Prior to Bt technology, farming involved a rigorous scouting schedule, spraying chemicals and still suffering insect damage despite best efforts. Failing to plant a refuge might put farmers back in the same boat.
A refuge provides a habitat for target insects to feed, mate and reproduce without being exposed to the Bt trait. Many insects die when they constantly feed on Bt traits, but those that survive will reproduce and have a higher change of creating offspring resistant to the Bt trait. If a refuge is available, there’s less chance for two resistant insects to mate, slowing the resistance process.
“When you ignore refuge, the only person who’s being hurt is the farmer themselves,” Jones says. “It just creates resistant insects faster and decreases yield.”
How do you know if your refuge is compliant? Each hybrid has the potential to have a different refuge requirement. Refuge requirements depend on number of traits, target insect and geography. More traits equal less refuge.
For example, if you’re only fighting one trait, such as corn earworm, the insect can build resistance faster. However, it’s harder to become resistant to two modes of action at the same time, so refuge requirements are less in that case.
Study the chart below to refresh your memory on common trait lineups and their corresponding refuge. Double check labels and ask your seed dealer to be certain.
You reap what you sow, and skipping refuge can expedite insect resistance. Careful stewardship helps preserve technology for future generations.
Refuge Requirements for Cotton
For Southern farmers, refuge requirements are often more strict. Cotton bollworm, also called corn earworm, is a bigger threat than in the upper Midwest.
“There is a greater risk of that insect developing resistance because it finishes two life cycles on Bt crops (corn and then cotton),” explains Jeff Gore, associate professor of research and Extension at Mississippi State University.
There is no structured refuge for cotton since studies prove there is enough natural non-Bt refuge for bollworm to reproduce, so Bt cotton traits get a break. Corn, however, has no natural refuge and requires a higher percent of structured refuge in areas where cotton is also grown. Hybrids with a single Bt trait require 50% structured refuge, and hybrids with two traits require 20% structured refuge.
“The reason for higher refuge all surrounds corn earworm,” Gore explains. “They complete their development on corn and move to cotton and soybeans and increase the selection pressure to Bt traits.”
Even with Bt, corn earworm/bollworm populations run rampant and cause significant damage, specifically to cotton. Most people spray insecticide one to two times each season to fight bollworms. Those who don’t might lose 100 lb. to 350 lb. of cotton per acre, Gore adds.
While corn earworm/bollworm does significant damage to cotton, there is no evidence they cause issues in corn. As a result, farmers who only plant corn are sometimes reluctant planting higher refuge.
“Across the southern U.S., compliance is generally low,” Gore says. “It’s getting higher, but corn farmers don’t see the benefit because the primary targets in corn are corn borers.”