By: Darrell Smith, Farm Journal Conservation and Machinery Editor
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.
That requires identical tillage practices because residue levels affect soil temperature, which influences insect development. Use the same fertility programs, including starter and sidedress fertilizer.
Plant your Bt corn and your refuge at the same time, so both hybrids are in the same developmental stage. "It isn’t necessary to plant a refuge each day you plant corn on consecutive dates," says University of Kentucky Extension entomologist Ric Bessin. "But you should plant at least one refuge for all the Bt corn planted over a four- to seven-day period."
If you’re planting your refuge as a block, consider planting that corn before you plant the rest of the field to the Bt hybrid, Smith suggests. That way, the minimum size for the refuge will be met if weather alters your planting schedule or strategy.
In irrigated areas, the nonirrigated pivot corners are the wrong place for a refuge, points out University of Nebraska Extension entomologist Thomas Hunt. Those plants will be less attractive to corn borers than the irrigated area—and your goal with a refuge is to produce susceptible corn borer moths.
5. Don’t mess up the math. Say you have a 100-acre field and your Bt hybrid requires a 20% refuge. That means you must plant 20 acres of refuge and 80 acres of the Bt hybrid. It does not mean you can plant 100 acres of Bt hybrid in the field and 20 acres of susceptible hybrid nearby.
6. You’re on your own. Refuge management is one situation where you can’t team up with a neighbor. Your refuge must be on your land because you can’t control the management of someone else’s crop, Hunt explains.
7. Stick with your plan. After you devise a refuge management plan, don’t keep it to yourself. Share it with your employees and suppliers.
"Everyone involved with your oper-ation must understand your plan," Ferrie says. "Your crop scout must know where your refuges are, so he can scout them effectively. If he thinks he’s scouting the refuge but is actually scouting the Bt hybrid, he may draw the wrong conclusions about insect populations. Your supplier must know where your refuge is, so it doesn’t get sprayed by accident and eliminate all of your susceptible insects."
The best-laid plans can fall apart during a hectic planting season. "If planting runs late and you wind up switching to earlier-maturing hybrids, you are responsible for any refuge requirements of the new hybrids," Ferrie says.
8. Think twice before you spray. "If you see a tremendous amount of corn borers or rootworms in your refuge and you decide to spray it, you must spray the entire field," Ferrie says. "The refuge is supposed to produce susceptible insects to mate with the resistant ones in the rest of the field. So if you kill those susceptible insects, you have to kill the resistant ones too."
Before you apply any insecticide on a refuge, consult the seed tag, your grower’s guide or your seed company representative to find out which treatments are permitted.
9. Evaluate insect pressure. Refuge-in-a-bag products—in which rootworm-susceptible and resistant seed is packaged together, eliminating the need to plant a separate refuge—can be a great convenience. "The concept works very well with low or moderate rootworm pressure, and there are many areas like that," Ferrie says.
"But with heavy rootworm pressure, some growers get frustrated with the amount of goosenecked corn plants. In those areas, it’s better to plant your refuge in a block and treat it with insecticide."
Refuge-in-a-bag products are also available for corn borer. They eliminate the need to plant a separate refuge in the Corn Belt. However, these products require a 20% block refuge if they are planted in cotton-growing regions of the U.S.
10. Use every tool. Every company provides a wealth of information—on the seed tag, in grower’s guides available from your seedsman and from the company website.
The National Corn Growers Association (NCGA) provides a free Insect Resistance Management calculator at www.irmcalculator.com. The calculator, a collaboration between seed companies and NCGA, features the latest options for refuge design, includes all commercial Bt products and lets farmers run field-by-field refuge planting scenarios. It’s designed to be used in conjunction with seed company stewardship guides.
Smartphone users can also access the tool. Go to www.irmcalculator.com from a hand-held device to be routed to a simplified version of the site.
More Refuge-Planting Tips
There are many resources to help farmers put an effective Insect Resistance Management (IRM) plan in place. "Proper planning ensures growers will continue to benefit from consistent insect protection, while being compliant with IRM requirements, an Environmental Protection Agency mandate," says Joanne Carden, Monsanto Company’s stewardship strategy lead. "Growers should call their seed representative or dealer if they have any questions concerning their refuge plan."
Here are some additional tips for refuge compliance, from the 2012 edition of Monsanto’s IRM Grower Guide:
- Plant the refuge at the same time you plant the Bt hybrid.
- To avoid mixing seed, clean all seed out of hoppers when switching between Bt and non-Bt hybrids.
- Adjacent and separate refuge fields must be planted and managed by the same grower.
- If the corn refuge is planted on rotated ground, the Bt hybrids must also be planted on rotated ground.
- If the corn refuge is planted on continuous corn ground, the Bt hybrid can be planted on either continuous-corn ground or on rotated ground.