More Bt hybrids are available, some with new traits, but does that mean you're killing more bugs for your buck? Reaping high rewards with the bug-busting Bt hybrids takes homework.

The biggest factor in determining which hybrids to grow is always yield, says Joe Lauer, agronomist at the University of Wisconsin. Lauer conducts yield trials on more than 500 hybrids each year at 13 locations across the state.

As a group, Lauer says Bt hybrids for European corn borer (ECB) yield well — usually at or above average. However, he's not yet sold on the yields for the relatively new corn rootworm (RW) Bt technology.

“To make the RW Bt pay you need a very specific situation where you're growing continuous corn or you've had significant problems with corn rootworm in the past,” says Lauer.

After one year of RW Bt hybrid testing, only a few performed well.

“The first year out of the blocks, the Bt RW event, in general, has yielded average to below average in university trials across the Midwest,” Lauer says. “Farmers should choose hybrids with above average yields.”

In Wisconsin trials, the average range between top and bottom ranked hybrids is 78 bu./acre. If half of that is the difference between an average hybrid and a top hybrid, Lauer says you could easily be giving up 20-30 bu./acre by choosing the wrong genetics.

A hybrid can only yield as well as its parent genetics, says Jon Tollefson, entomologist at Iowa State University, but for farmers with high-rootworm pressure, a RW Bt may be a good buy.

In three rootworm trials across Iowa last year, Tollefson tested a YieldGard RW Bt hybrid that averaged a 34 bu./acre advantage over the untreated check crop with similar genetics. In a high-rootworm pressure, high-heat, low-moisture stress situation the difference was even greater — 44 bu./acre. But, in a field trial where there was only low-to moderate-rootworm pressure, the YieldGard hybrid showed no statistical difference from the check hybrid.

“If you actually have rootworms, then it would be worth the money to invest in the rootworm Bt technology,” says Tollefson.

Kevin Steffey, entomologist at the University of Illinois, points out that if farmers don't study their fields, they may spend extra money on a non-existent problem.

“Bt corn for rootworm control, soil insecticides and insecticidal seed treatments are all designed to protect the root system from rootworm larval damage,” Steffey says. “You can make a decision to use Bt corn for rootworm control based on the counts of adult rootworms from the previous year. That's the recommendation we've made for decades.”

Steffey says a little scouting is all it takes to make the right decision. During mid-July to late August in corn on corn, growers should count the number of rootworm beetles per plant and compare those numbers to existing thresholds. If the field is below threshold, a grower doesn't need to spend money on rootworm control the next year.

“No insecticidal seed treatments, soil insecticides or RW Bts are required,” says Steffey “On the other hand, if the field is above threshold, growers can determine what's best to use based on the beetle counts.

“If a field is way above threshold, you'd be better off using a soil applied insecticide or a Bt rootworm hybrid. But for light-to moderate-rootworm pressure, the higher rate seed treatment does fine,” he says.

Steffey says in three decades of three independently conducted studies in corn on corn in three different states — Iowa, Illinois and Indiana — 50% of the fields didn't show enough rootworm pressure to cause enough damage to offset the cost of control.”

Insects Controlled By Available Bt Traits
European corn borer Southwestern corn borer Southern cornstalk borer Corn earworm Fall armyworm Stalk borer Western bean cutworm Black cutworm Western corn rootworm Northern corn rootworm Mexican corn rootworm Market Choices hybrid
Herculex I (All Herculex hybrids are Liberty Link) C C S C C C X
YieldGard Corn Borer C C C S S S
YieldGard Corn Borer with Roundup Ready C C C S S S X
YieldGard Corn Borer with Liberty Link C C C C S S X
YieldGard Rootworm C C C X
YieldGard Rootworm with Roundup Ready C C C X
YieldGard Plus C C C S S S C C C X
C=Control, S=Suppression
Market Choices hybrids - The Market Choices program identifies those hybrids that are fully approved for food and feed use in the United States and Japan, but are still awaiting the necessary approvals in the European Union. Growers that plant Market Choices hybrids must use appropriate markets for this grain including feedlots, feed mills, on-farm feeding, or work with grain handlers who agree to accept the grain. Growers should contact their local seed dealers and grain handlers for more stewardship details.
SOURCES: DOW AGROSCIENCES AND MONSANTO

In other words, Steffey says, “Just because you have bugs doesn't mean it always pays to fight them. If you do, they may cause more damage to your wallet than your corn.”

If you live in an area where the western corn rootworm variant lays its eggs in soybean fields, you can set up yellow sticky traps and make decisions based on thresholds in those fields, too, says Steffey.

Todd DeGooyer, trait technology manager for Monsanto, says he believes there's a benefit to the rootworm trait.

“YieldGard Rootworm technology delivers some important benefits to growers and we are witnessing strong root protection out of the technology again this season,” he says. “I think it's important that farmers see how it works on their farm.”

While you can scout your fields to determine if you should plant a RW Bt, the decision to plant an ECB hybrid is entirely based on your field's past corn borer pressure. If you historically have economic levels of corn borers, planting an ECB Bt can make sense, says Steffey.

According to Bob Navratil, technical information manager for NK Brand Seeds, there's a 7.7 bu./acre yield advantage with an ECB Bt over a non-treated conventional hybrid. “Year in and year out we've seen a benefit that exceeds the cost of the seed premium with NK Brand YieldGard Bt hybrids,” says Navratil. “Every grower might not see a 7.7 bu. difference, but in 88% of 3,000-plus rated comparisons we saw corn borer damage and measured a yield advantage.”

He adds that ECB Bts are a boon because corn borers have been hard to control with other methods.

Brent Wilson, technical information manager for Pioneer Hi-Bred International, says that while genetics should always be first priority, growers need to understand that ECB hybrids control different insects.

The Bt proteins are slightly different. Wilson says where you are located and what your pest pressures are should influence your hybrid choice. Pioneer sells both types of hybrids, including those with Monsanto-licensed YieldGard traits or those with Herculex I traits developed in collaboration with Dow AgroSciences. (See chart.)

“It comes down to the total package,” says Wilson. “Farmers need to ask, ‘Does the hybrid have the yield potential that I want for my acres? Does it have the agronomic traits that are important to my growing environment? And, does it have the insect protection that I really need to control the insects in my area?’”

With increasing interest surrounding the spread of western bean cutworm in his home state of Iowa, Wilson says Herculex is getting attention because YieldGard ECB doesn't control the secondary pest.

“You can select either a YieldGard ECB or a Herculex I hybrid and both are going to provide tremendous control of European corn borer and southwestern corn borer — their primary targets,” says Stephen Smith, agronomy service manager for Mycogen Seeds, which sells Herculex hybrids. “However, as you look at the different insects each controls, the Bts begin to differentiate themselves. If you're interested in black cutworm or western bean cutworm, the Herculex I hybrid will provide protection where YieldGard ECB hybrids will not.”

Currently, Monsanto is the only company that has an approved rootworm trait and, consequently, the only company licensing RW Bts and an ECB/RW stack, known as YieldGard Plus. Dow AgroSciences and Pioneer expect to have Herculex RW and a stacked trait of Herculex I and Herculex RW, called Herculex XTRA, for 2006, pending approvals. Syngenta expects to have its own NK Brand RW traits approved during that same time frame.

Monsanto's DeGooyer says the company is looking at the synergistic effect of using the ECB and RW traits together, in its product YieldGard Plus.

“Growers have increasingly told us that they enjoy the flexibility of stacked traits and YieldGard Plus offers a new tool with above and below the ground protection against these corn pests,” he says, “We think farmers will see the value of using it to protect their corn.”