Drop Those Volunteers

The term "Bt" could stand for "big trouble" in the years ahead if growers aren’t careful in their use of biotech corn, says a Purdue University entomologist.

Corn varieties containing Bacillus thuringiensis, or Bt, genes to control corn rootworms and corn borers — and genetically modified to withstand Roundup herbicide — could become more susceptible to rootworms unless growers keep soybean fields free of volunteer corn and continue planting refuge acres, says Christian Krupke.

"We need to stay a step ahead of rootworm resistance development," he says. "If there’s one thing we know about insects, it’s that they figure out a way to adapt to whatever we throw at them."

Rootworms are a major threat to corn crops, costing growers about $1 billion a year in yield losses and control expenses. For example, about 30 percent of Indiana’s estimated 6.45 million corn acres were planted to multi-trait biotech varieties this year, including the Bt/Roundup "triple stacks."

While transgenic varieties have helped growers boost corn yields, those varieties could unintentionally produce stronger, tougher-to-control rootworms when growers rotate their cornfields to soybeans the following year, Krupke says. Rootworms feeding on volunteer corn — maverick plants that grow from seed produced by the previous year’s crop — are exposed to Bt but at less-than-toxic levels.

"What we found was that in areas where triple stack corn was planted in 2006 and soybeans in 2007, we had a great deal of volunteer corn in some of those fields," Krupke says. "Most of that volunteer corn showed up as being Roundup Ready and as having the Bt gene for rootworm.

"The problem is that the Bt, for whatever reason, isn’t expressed at the same level as Bt that you’d get in off-the-shelf corn," he continues. "So you get a lot of rootworm larvae eating that volunteer corn, and they are able to survive on it. That’s a concern because now you’re getting insects exposed to sub-lethal doses of Bt that survive to mate and lay eggs and possibly develop stronger offspring. That is exactly what we don’t want."

Volunteer corn is considered a weed and is usually controlled with herbicides. Controlling that corn becomes more difficult when it is both resistant to glyphosate, the active ingredient in Roundup, and growing in Roundup Ready soybeans. In recent years about 90 percent of Indiana soybean acres have been planted to Roundup Ready varieties.

"Most soybean growers have relied on Roundup as their No. 1 — and sometimes only — weed control for a long, long time," Krupke says.

Growers have several herbicide options for controlling volunteer corn, says Bill Johnson, Purdue Extension weed scientist.

"To control volunteer Roundup Ready corn in soybeans, farmers should use Assure II, Select Max, Fusion, or Raptor tank-mixed with glyphosate," Johnson says.

Another factor that could hasten rootworm resistance to Bt corn is improper or insufficient planting of refuge corn. Planting refuges alongside Bt corn crops is required by law.

"A refuge is anything that is not Bt corn," Krupke says. "So when you plant Bt corn for rootworm or corn borer, for every 80 acres you plant of the Bt you have to plant 20 acres of the refuge.

"The thought behind the refuge is that you have some insects in that refuge that are never exposed in their lifetime to Bt," says Krupke. "They never have an opportunity to develop resistance to it. The only way insects develop resistance is by exposure. The more you expose them, the greater the pressure is for them to be resistant. So you want to generate some insects that are never exposed to Bt so that they will mate with the ones that are exposed to Bt to dilute the chances of those offspring being resistant."

Killing all rootworms by planting 100 percent of acres in Bt corn is neither the objective, nor is it possible, Krupke says. "If you expose the entire rootworm population at the same time to Bt, the insects will either have to become resistant or go extinct," he explains. "We have made zero species of insects extinct, so you can figure out which way it is going to go."

Even in cornfields where refuge acres were planted, Krupke and fellow Purdue entomologists have found troubling signs.

"We’ve looked at the relative sizes of rootworm beetles coming out of the transgenic and refuge corn and found some large females coming out of the transgenic blocks," Krupke says. "That is important because large females tend to lay more eggs and are preferred by the male beetles because they lay more eggs."

Growers need to remain vigilant when they plant Bt corn to ensure the technology is around for a long time, Krupke says. "If we don’t do the things that we need to do, then we’re eventually going to have products that are not effective against rootworm," he says. "The two primary things would be to continue planting the refuge and, in areas where you are rotating corn with soybeans, clean up any volunteer corn that you have in the field. You need to do the latter because volunteer corn is a host, and that’s where rootworms can develop. There will be a lot of eggs in those first-year soybean fields that were in corn the year before."

(Source: Purdue University)
 

Leave a Reply

Latest News
EmployeesOABA Program Develops Future Generation Of Agribusiness…
September 29, 2016
The Ohio AgriBusiness Association will select up to 25 promising leaders to participate in a leadership enhancement program early next Read More
ManagementThoughts on CropLife America and the PSM Appeal
September 29, 2016
Editors Paul Schrimpf and Eric Sfiligoj talk about the recent CropLife America annual meeting and the successful appeal of the Read More
Corn Field
Industry NewsMarrone Bio Innovations’ SVP And Chief Sustainability O…
September 29, 2016
Marrone Bio Innovations, Inc., a leading provider of effective and environmentally responsible pest management and plant health products, announced today Read More
Young Corn Field
StewardshipStudy: Ohio Farmers Doing ‘A Good Job Of Managing…
September 27, 2016
Leaders from Ohio’s largest grain farming organizations announced today that Ohio farmers are doing their part in effectively managing phosphorus Read More
Growmark FS Outlet
Industry NewsGROWMARK To Purchase Suncor’s Share Of UPI
September 26, 2016
GROWMARK and Suncor have reached an agreement in which GROWMARK will purchase Suncor’s 50% interest in UPI, Inc. in Ontario, Read More
Corn Field
Eric SfiligojFacing Ag Industry Challenges
September 26, 2016
At the 2016 annual Mid America CropLife Association (MACA) meeting in September, a pair of crop protection company representatives discussed Read More
Syngenta Seedcare Institute
Seed/BiotechSyngenta Opens New North America Seedcare Institute In …
September 23, 2016
Syngenta unveiled its new Seedcare Institute in Stanton, MN, during a recent grand opening celebration. More than 150 industry leaders, Read More
StewardshipMonsanto Invests $1.6 Million In System To Quantify Gre…
September 23, 2016
The USDA – Natural Resources Conservation Service (USDA-NRCS) recently awarded the National Corn Growers Association (NCGA) and its Soil Health Read More
Pipe rack
LegislationCourt Sides With Ag Retailers On PSM
September 23, 2016
The D.C. Court of Appeals has ruled the Occupational Safety and Health Administration violated the Occupational Safety and Health Act when Read More
ManagementPacific Coast Fertilizer Announces Interest In Longview…
September 22, 2016
Pacific Coast Fertilizer LP (PCF) announced at the Cowlitz Economic Development Council board of directors meeting its interest in developing Read More
Young corn plants in soil
UncategorizedCool Planet Raises Additional $9 Million To Commerciali…
September 22, 2016
Cool Planet has announced the first close of a new financing round to commercialize the company’s Cool Terra Engineered Biocarbon Read More
Crop InputsJim Loar Promoted To President And CEO Of Cool Planet
September 22, 2016
In a move that reflects and reinforces the company’s commitment to the agricultural market, the Cool Planet board of directors Read More
BlendersNorth Dakota Coop Debuts Dry Fertilizer Plant
September 22, 2016
North Central Grain Cooperative has begun operations at a new dry fertilizer plant at its Rolla, ND, site. It is Read More
Crop InputsMonsanto, Bayer Officials Defend Proposed $66 Billion M…
September 21, 2016
Top officials for Monsanto and Bayer defended their proposed $66 billion merger before skeptical senators on Tuesday, insisting that the Read More
ManagementUpcoming Shows & Recent Events
September 19, 2016
Editors Paul Schrimpf and Eric Sfiligoj talk about upcoming trade shows and events and review the Mid America CropLife Association Read More
Industry NewsVerdesian Life Sciences Appoints New CEO
September 19, 2016
Verdesian Life Sciences, a plant health and nutrition company, today announced that its board of directors has named Kenneth M. Avery Read More
Corn
Crop InputsEPA Settles With Syngenta For Alleged Multi-Regional Pe…
September 19, 2016
The U.S. EPA has announced a multi-region settlement with Syngenta Crop Protection, LLC (Syngenta) in Greensboro, NC, for alleged violations of Read More
ManagementMerger Mania
September 16, 2016
Editors Paul Schrimpf and Eric Sfiligoj discuss this week’s mega-ag mergers of Bayer and Monsanto and Potash and Agrium. Read More