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

Featured Stories

FertilizerFall Fertility 2014: Forecasting Fertilizer Use
September 7, 2014
Great crops this year have tapped the soil, and fall work is definitely called for, but how challenging will that get? Read More
CropLife 100CHS To Build $3 Billion Fertilizer Plant In North Dakota
September 5, 2014
The fertilizer plant in Spiritwood will be the single largest investment in CHS history, as well as the single largest private investment project ever undertaken in North Dakota. Read More
CropLife 100Pinnacle Acquires East Kansas Chemical
September 2, 2014
Ranked 82nd on the CropLife 100, East Kansas Chemical will operate as part of Pinnacle's Performance Agriculture brand. Read More
CropLife 100Pinnacle Acquires California-Based Retailer
August 29, 2014
Pinnacle Agriculture Holdings will acquire Kerman Ag Resources, Inc., which will operate under Pinnacle's Performance Agriculture brand. Read More

Trending Articles

CropLife 100CHS To Build $3 Billion Fertilizer Plant In North Dakota
September 5, 2014
The fertilizer plant in Spiritwood will be the single largest investment in CHS history, as well as the single largest private investment project ever undertaken in North Dakota. Read More
EquipmentNew Holland Acquires Miller-St. Nazianz
September 3, 2014
The assets of Miller acquired as part of the transaction will become part of New Holland Agriculture, a CNH Industrial brand, building on a successful four-year partnership between the two companies. Read More
CropLife 100Pinnacle Acquires East Kansas Chemical
September 2, 2014
Ranked 82nd on the CropLife 100, East Kansas Chemical will operate as part of Pinnacle's Performance Agriculture brand. Read More
MAGIE 2014 ShowStopper
EquipmentJohn Deere Again Wins MAGIE ShowStopper Award
August 25, 2014
For the second consecutive year, John Deere was honored at the Midwest AG Industries Exposition (MAGIE) for its new R4045 sprayer. Read More
ManagementExpert To Discuss Farmland Value, Rent At Farm Science Review
August 18, 2014
While cropland values in Ohio increased in the past two years, they have remained flat in 2014, declining in some cases, according to an Ohio State University agricultural economist. Read More
EquipmentAdvance Your Technology IQ At MAGIE
August 13, 2014
The Midwest AG Industries Exposition (August 20-21) is the place you need to be to see, study and evaluate how new advances in the equipment, operations, crop protection and fertility sectors can help your business prosper. Read More

Latest News

CropLife 100Pinnacle Acquires Kansas-Based Cedar Ridge Supply
September 16, 2014
Cedar Ridge Supply will operate as part of Pinnacle's Performance Agriculture brand. Read More
StewardshipSecretary Vilsack Highlights Innovative Conservation Ef…
September 15, 2014
Nearly $16 million in Conservation Innovation Grants (CIGs) will be awarded to 47 organizations to help develop cutting-edge ideas to accelerate innovation in private lands conservation. Read More
Seed/BiotechSyngenta Responds To Cargill Lawsuit
September 15, 2014
Syngenta believes that the lawsuit is without merit and strongly upholds the right of growers to have access to approved new technologies. Read More
Equipment2014 Farm Science Review Launches Mobile App
September 15, 2014
Smartphone and tablet users planning on attending the 2014 Farm Science Review can now download this year’s customized mobile application. Read More
CropLife 100Southern States Coop Grower Sets Georgia Soybean Yield …
September 15, 2014
Georgia farmer Randy Dowdy's soybeans yielded an astonishing 110.66 bushels per acre, crushing the previous record of 82 bushels-per-acre. Read More
NIMITZ Treated vs Untreated pepper plant
InsecticidesNIMITZ Nematicide Approved By EPA
September 12, 2014
NIMITZ is a novel, non-fumigant nematicide with simplified application features, user safety and an active ingredient with a unique mode of action. Read More
InsecticidesMarrone Bio Innovations Receives Patent For Chromobacte…
September 11, 2014
The patent is the first step for MBI in developing a commercially viable product to inhibit infestations of corn rootworm larvae across America and other regions. Read More
HerbicidesDow AgroSciences: Keeping The Pipeline Stocked
September 11, 2014
Dow AgroSciences is embracing product diversity to drive the company’s future. Read More
CropLife 100CHS Is Official Partner Of New St. Paul Ballpark
September 10, 2014
The new ballpark in St. Paul, MN, officially became CHS Field with Twin Cities-based CHS Inc. revealed as the naming rights partner. Read More
EquipmentHagie Honors Farming Stewardship Leaders
September 10, 2014
The Iowa Farm Environmental Leader award recognizes Iowa farmers as environmental leaders that are committed to healthy soils and improved water quality. Read More
Precision AgPlantBeat: Your Plants’ Pulse In The Palm Of Your Han…
September 10, 2014
A new agronomic monitoring and recommendation service from Phytech could rewrite the book on real-time plant health status monitoring. Read More
StewardshipCCAs Making Headway With 4R Program In Lake Erie Wester…
September 9, 2014
Certified Crop Advisers are implementing the 4R Nutrient Stewardship Certification program in Lake Erie's Western Basin to improve water quality. Read More
MicronutrientsMicronutrients Going Macro
September 9, 2014
Between 2014’s fantastic growing conditions and a heightened awareness on plant nutrition, the major players in micronutrients are gearing up for another big year. Read More
Crop InputsFMC Announces Cheminova Takeover
September 8, 2014
FMC Corporation today announced that it has signed a definitive agreement to acquire Cheminova, a wholly owned subsidiary of Auriga Industries. Read More
HerbicidesValent’s Fierce XLT Herbicide Receives EPA Approv…
September 8, 2014
Valent U.S.A. Corp. announced today that Fierce XLT Soybean Herbicide is now federally registered for preemergence weed control in soybeans Read More
Eric SfiligojIndustry Consolidation Set To Increase Going Forward
September 8, 2014
As the agricultural marketplace moves into fall, one observer predicts the pace of consolidation will grow at all levels. Read More
LegislationCropLife America Leaders Address Regulatory Landscape, …
September 8, 2014
As CropLife America enters its 81st year, the organization’s leaders have seen another period of rapid and visible policy and public issue activity. Read More
FertilizerFall Fertility 2014: Forecasting Fertilizer Use
September 7, 2014
Great crops this year have tapped the soil, and fall work is definitely called for, but how challenging will that get? Read More