The purpose of refuges is to enable some susceptible insects to survive. Mating with Bt-resistant insects prevents a resistant race from developing.
Refuge management will help your hybrids work effectively and keep you in compliance with regulators
No one likes the fact that new technology usually comes with a price tag called a "learning curve." But who wouldn’t want to simplify their pest management system and boost yields at the same time by using a Bt hybrid? The good news is, once you understand the concept of "refuge," the rest is all downhill.
Though hybrids containing the Bacillus thuringensis (Bt) protein simplify pest control by eliminating the need for most soil-applied and foliar insecticides, they create a need for refuges. These consist of a certain number of acres planted to non-Bt hybrids, which are essential to
preventing insects from developing resistance to Bt hybrids. Pesticide resistance—by weeds, diseases and insects—is the biggest agronomic issue facing producers in 2012, says Farm Journal Field Agronomist Ken Ferrie. "The better stewards we are of Bt hybrids, the longer we’ll be able to use them," he says.
A certain percentage of insects is resistant to any pesticide, Ferrie explains. "Back when we applied soil rootworm insecticides, in a band about 7" wide and 4" deep, they protected only the area around the crown root of a corn plant," he says. "Many rootworms survived; the few that were naturally resistant to the insecticides mated with the many susceptible insects, so resistance was not passed on as easily. But with Bt hybrids, all the insects that survive are naturally resistant. When we plant these hybrids, we are selecting for resistant insects."
Planting refuge areas to a non-Bt hybrid ensures that susceptible insects survive, so resistance does not become a problem. Besides that practical aspect, the Environmental Protection Agency makes planting a properly sized refuge a legal requirement for using Bt hybrids.
With resistance at stake, noncompliance is cause for concern, Ferrie says. But some farmers negate the value of their refuge by failing to plant sufficient acres, failing to design their
refuge correctly or not managing it properly after planting.
"Problems are more accidental than intentional," Ferrie says. "But some farmers don’t realize that they aren’t in compliance."
Refuge management can be complicated. Acreage requirements for Bt hybrids range from 5% to 20% in corn-growing areas and from 20% to 50% in cotton-growing areas. Hybrids containing two resistance modes of action for the same insect might require a smaller refuge. Hybrids containing resistance to two pests require a refuge for each insect.
Here are some tips to make your refuge management successful:
1. It’s your responsibility. "Start by choosing the best-yielding genetics for your farm," Ferrie says. "If those hybrids come with Bt traits that you need, that’s a bonus. But sometimes the best-yielding hybrids come with traits you don’t actually need on your farm. In that case, you still are responsible for planting the required refuge."
2. Work with your seed supplier. "Good seedsmen understand the requirements for their hybrids, and they can help you plan your refuges," Ferrie says. "Your seed company representative will know the distance requirements for hybrids and various ways to lay out the refuge.
"He or she can advise you on what hybrid to plant in order to complement your resistant hybrid. I’ve seen farmers run into problems when they purchase a refuge hybrid with flowering dates different from the Bt hybrid they planted in the rest of the field."
3. Choose the best hybrid for a refuge. Your refuge hybrid should have similar agronomic characteristics to your Bt hybrid, especially early vigor, maturity and plant height, says
Michael Smith, senior North American product stewardship manager for Pioneer Hi-Bred. That way, it will be as attractive to adult insects as your Bt hybrid. It will also let you harvest both hybrids at the same time.
4. Manage hybrids identically. You want the Bt hybrid and your refuge hybrid to be equally appealing to insects, Smith emphasizes.
- March 2012