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
Soybean field
Crop InputsNufarm Teams Up With John Deere Financial
January 19, 2017
Nufarm and John Deere Financial have teamed up to help farmers grow a better tomorrow. This program helps make purchases Read More
Sonny Perdue
LegislationTrump Formally Picks Perdue As Agriculture Secretary
January 19, 2017
U.S. President-elect Donald Trump officially announced Sonny Perdue as his choice for secretary of agriculture on Thursday, selecting a former Read More
ManagementPresident Trump, Wisconsin Review, and a Dow-DuPont Upd…
January 18, 2017
Editors Paul Schrimpf and Eric Sfiligoj reflect on a new administration, a recent winter show, and crop protection company mergers. Read More
Industry NewsBayer, MS Technologies Get China Approval For Balance G…
January 18, 2017
MS Technologies and Bayer have received import approval from China for Balance GT soybeans. The new Balance GT Soybean Performance Read More
Werner Baumann, Bayer AG, and Hugh Grant, Monsanto
Industry NewsReport: Monsanto, Bayer CEOs Among Latest to Make Trump…
January 18, 2017
The chief executive officers of German chemical giant Bayer AG and U.S. seed behemoth Monsanto, Werner Baumann and Hugh Grant, Read More
Giant Ragweed
HerbicidesStudy: Focusing On Weed Seedbank Can Help Manage Herbic…
January 18, 2017
Researchers writing in the latest issue of the journal Weed Science provide important insights on the control of herbicide-resistant giant Read More
Management3 Financial Trends To Watch In Agriculture
January 17, 2017
I recently had the opportunity to attend a meeting of credit managers for Midwest ag supply and input companies, in part Read More
Andersons Retail Store
CropLife 100The Andersons To Close All Retail Stores; Shutdown Does…
January 16, 2017
In a stunning announcement to the Toledo area, The Andersons Inc. said on Sunday that it would close its two Read More
Trimble TMX-2050 In-Cab Display
Eric SfiligojPrecision To Lead Agriculture In 2017?
January 16, 2017
Another new year is upon us! And I’m certain I speak for many in the agricultural world when I say Read More
Corn
Eric SfiligojThe Mood From Madison? In A Holding Pattern
January 16, 2017
Last week, I had the chance to attend the annual Wisconsin AgriBusiness Classic show in Madison, WI. It’s been a Read More
Syngenta Sign
Crop InputsAccenture Helps Syngenta Transform Its Global Logistics
January 13, 2017
Syngenta, a leading agriculture company, has collaborated with Accenture to design and implement a new digital logistics operating model across Read More
Fall Creek Seth Harden The Nature Conservancy
StewardshipLocal Farmers’ Watershed Initiative: Continuous Improve…
January 13, 2017
The goal in the Big Pine Watershed Project is to more intentionally do what local farmers and responsible ag retailers Read More
HerbicidesEPA Expands Enlist Duo Herbicide Registration To 34 Sta…
January 13, 2017
The U.S. EPA has expanded the geography for application of Enlist Duo herbicide from 15 to 34 states. This means Read More
Olson Ag Enterprise
CropLife 100Wilbur-Ellis Acquires Nebraska Seed Retailer
January 13, 2017
Wilbur-Ellis’ Agribusiness, a recognized leader in precision agriculture technology and the distribution and marketing of plant protection, seed and nutritional Read More
ManagementDeere-Precision Planting Update and the Ag Secretary Wa…
January 12, 2017
Editors Paul Schrimpf and Eric Sfiligoj provide the latest on the court date for John Deere/Precision Planting and the quest Read More
Monsanto sign
Seed/BiotechMonsanto, NRGene Form Agreement For Big Data Genomic An…
January 12, 2017
Monsanto Co. and NRGene have announced that the companies have reached a non-exclusive, multi-year global licensing agreement on NRGene’s genome-analysis Read More
AGCO Custom applicator
SprayersAGCO, Asmark Institute To Offer Training For Beginning …
January 11, 2017
AGCO Corp. and the Asmark Institute are collaborating to offer a new training program dedicated to educating and developing custom Read More
ManagementAg Land Values In Limbo In 2017
January 10, 2017
Several factors will come into play in 2017 that will determine the direction of land values. Randy Dickhut, senior vice Read More