Like applied pesticides, bacillus thuringiensis, known as Bt traits, protects crops from insect infestations. And just like applied crop protection products, certain management practices must be followed to preserve Bt traits as a viable pest control option.

Planting a refuge is mandatory to remain in compliance with Bt insect resistance management plans and delay the development of insect resistance to Bt technology. In cotton-growing counties where integrated refuge products are planted, a separate structured refuge must be planted. Farmers who do not to follow refuge requirements are risking Bt resistance development.

“The biggest problem for resistance management is a lack of compliance with refuge requirements,” says Francis Reay-Jones, professor of entomology and IPM coordinator at Clemson University. “For Bt corn hybrids that express two or more Bt toxins for above-ground pests, the size of the non-Bt refuge should be 20% of the total corn planted, located within or adjacent to the Bt field, or within a half mile of the Bt corn.” 

Reay-Jones, who holds a doctorate in entomology from Louisiana State University, says that in areas that require a structured refuge, planting refuge is one of the only management options available to delay Bt resistance.

“Other than deciding not to plant a Bt crop, planting a non-Bt refuge is the only method available to delay the development of resistance. The development of resistance in target pests is a major threat to Bt crops,” he says.

By planting a non-Bt refuge next to Bt corn, when insects feed on the non-Bt crop, they remain susceptible to the Bt traits. If an insect survives after feeding on Bt corn, the large majority of. insects available to mate with are Bt susceptible, making it less likely the offspring of those insects will carry Bt trait resistance.

Bt resistance comes with its fair share of consequences, such as plant injury and Bt technology becoming a less effective management strategy. Reay-Jones says when target pests develop resistance to a Bt toxin there is an increased level of plant injury and the Bt technology becomes less effective as a management strategy. Implementing management practices to limit the risk of resistance and preserve Bt technology is critical.

“Currently, there are a limited number of Bt toxins that are used in both Bt corn and cotton,” Reay-Jones says. “Resistance has already been documented to several Bt toxins in corn earworm populations in the southern U.S., and only a single Bt toxin provides very good levels of control, and it is currently available commercially in both corn and cotton. Good stewardship of Bt traits by planting non-Bt refuge is essential to preserve the efficacy of Bt technology.”

When planting Bt corn, an insect-resistance management program is required, which includes planting a refuge. The size of the refuge, distance of refuge from the Bt crop, and insecticide usage guidelines all depend on the Bt traits chosen for use in the field. Refer to seed technology use guides or stewardship agreements for specific refuge configuration options and compliance requirements.

For more information about Bt resistance management, and to find out if your county requires structured refuge, visit https://iwilltakeaction.com/insects/corn/principles-of-resistance.