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
ManagementWashington Update, Dow-DuPont Earnings, and the Passing…
April 27, 2017
Editors Paul Schrimpf and Eric Sfiligoj talk about the latest Beltway news, crop protection company 1st quarter numbers, and the Read More
BRANDT
CropLife 100Former PotashCorp COO Joins BRANDT Board
April 27, 2017
BRANDT has announced the appointment of another industry veteran to its board of directors. David Delaney, most recently EVP and Read More
Syngenta headquarters in Basel, Switzerland
Crop InputsFortune: Inside China’s $43 Billion Bid for Food …
April 26, 2017
(Via Fortune.com) The worst famine in human history occurred in China from 1959 to 1961. An estimated 34 million people Read More
Syngenta Sign
Crop InputsSyngenta Announces Changes in Board of Directors
April 26, 2017
ChemChina and Syngenta announced changes relating to the new Board of Directors of Syngenta following the closing of the ChemChina Read More
Crop InputsBioSafe Systems Introduces PerCarb Broad-Spectrum Bacte…
April 26, 2017
BioSafe Systems announces PerCarb (Sodium Carbonate Peroxyhydrate), a new alternative to potassium bicarbonate and lime sulfur products for use in Read More
Deere Twitter
EquipmentTop 10 Twitter Pics for #Plant17
April 26, 2017
Despite some wet weather in parts of the Midwest, growers and ag retailers are working feverishly to plant this year’s Read More
Donald Trump
Crop InputsTrump Targets Agriculture with Latest Executive Order
April 26, 2017
(Via UPI.com) President Donald Trump on Tuesday took executive action in an effort to help grow the domestic agriculture industry Read More
AGCO Ratliff featured
EquipmentAGCO Mourns Passing of Company Founder, Industry Vision…
April 25, 2017
AGCO Corp., a worldwide manufacturer and distributor of agricultural equipment and solutions, mourns the passing of founder and former President, Read More
Engenia soybeans
Crop InputsINNVICTIS CROP CARE Introduces VANDAL MOC Soybean Herbi…
April 25, 2017
INNVICTIS CROP CARE, LLC has announced the U.S. EPA registration for VANDAL MOC, a combination of sulfentrazone plus metolachlor. VANDAL Read More
Kochia
HerbicidesINNVICTIS CROP CARE Launches STAVE Post-Emerge Broadlea…
April 25, 2017
INNVICTIS CROP CARE, LLC has introduced STAVE as the newest addition to­ its expanding portfolio. STAVE will be a great Read More
Sonny Perdue
LegislationSonny Perdue Confirmed by Senate as Next Agriculture Se…
April 25, 2017
After months without a secretary of agriculture, the Senate voted Monday evening to confirm former Georgia Gov. Sonny Perdue to Read More
BPIA logo
Seed/BiotechBPIA Files Comments with USDA
April 24, 2017
The Biological Products Industry Alliance (BPIA) has filed comments with the USDA’s Animal and Plant Health Inspection Service (APHIS) Plant Read More
Eric SfiligojHope for Application Equipment Sales
April 24, 2017
The old saying goes that a “rising tide lifts all boats.” If this is indeed the case, then things may Read More
Stewardship video screenshot
ManagementNew Video Raises Awareness of 2,4-D Stewardship
April 24, 2017
A new public service video developed and produced by the 2,4-D Research Task Force, in conjunction with the American Soybean Read More
ManagementAn Inside Look at Award Winning Ag Retailer Gar Tooteli…
April 20, 2017
CropLife Editor Eric Sfiligoj discusses An Inside Look at Award Winning Ag Retailer Gar Tootelian Read More
Students Soybean Field
Industry NewsMACA Announces 2017 Young Leader Scholarship Recipients
April 19, 2017
The Mid America CropLife Association (MACA) Board of Directors selected 11 college students to receive the MACA Young Leader Scholarship Read More
Growmark FS Outlet
SoftwareKnoa Software Solution Helps GROWMARK Boost System Perf…
April 19, 2017
Knoa Software, a leading provider of user experience management (UEM) software, has announced that GROWMARK, Inc., a regional agricultural cooperative Read More
Crop InputsFBN Publishes ‘Voice of the Farmer’ Agricul…
April 17, 2017
Farmer’s Business Network (FBN) released today its “The Voice of the Farmer”, which the company is describing as “a special Read More