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

CropLife 100South Dakota Wheat Growers To Add Grain-Agronomy Facility
September 26, 2014
Planned to be constructed in Kennebec, the facility will be located along the soon-to-be rehabilitated line of heavy-rail service from Chamberlain to Presho. Read More
FertilizerCF Industries Confirms Merger Of Equals Discussions With Yara International
September 23, 2014
CF Industries Holdings, Inc. has confirmed that it is in preliminary discussions with Yara International regarding a potential merger of equals transaction. Read More
Seed/BiotechUSDA Approves Enlist Following Rigorous Review
September 18, 2014
Dow AgroSciences now awaits EPA registration of Enlist Duo herbicide, the companion herbicide to the Enlist traits, which is expected in the near future. Read More
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

Trending Articles

Equipment2014 Product Of The Year Voting
September 19, 2014
Many new products were introduced to the ag retail marketplace this year. From this group, CropLife IRON and its consulting partners have selected five finalists for the Product of the Year award. Please cast your vote today to help us determine the winner. 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
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

Latest News

Syngenta
Crop InputsSyngenta Launches Plant Breeding Academy
October 1, 2014
Syngenta announces the release of its Breeding Academy, a global initiative designed to enable the continued development of scientists at Syngenta and beyond. Read More
FertilizerFertilizer Outlook And Technology Conference Set For No…
September 30, 2014
Conference participants can expect to gain perspective on the outlook for agriculture and major fertilizer materials and inputs from industry experts. Read More
MicronutrientsVerdesian Acquires Micronutrient Supplier
September 30, 2014
Verdesian Life Sciences has acquired QC Corp., a producer and supplier of granular and dry micronutrients and ferrous sulfate products. Read More
Eric SfiligojHearing From Young Ag Voices
September 30, 2014
Potential future leaders in ag retail had the chance to shine at the recent Mid America CropLife Association meeting. Read More
WebinarsUpcoming Webinars
September 30, 2014
Register for one of our upcoming Webinars or access our archive of past Webinars to view recordings of presentations that may be of interest to you. Read More
Crop InputsSyngenta Appoints New Chief Operating Officer
September 29, 2014
Jon Parr will succeed retiring COO John Atkin at the end of the year. Read More
CropLife 100South Dakota Wheat Growers To Add Grain-Agronomy Facili…
September 26, 2014
Planned to be constructed in Kennebec, the facility will be located along the soon-to-be rehabilitated line of heavy-rail service from Chamberlain to Presho. Read More
CropLife 100GROWMARK Announces Vice President Appointments
September 25, 2014
Two individuals have been appointed Vice President positions on the GROWMARK executive team. Read More
FertilizerFertilizer Industry Organizations Join Global Alliance …
September 25, 2014
The Fertilizer Institute, the International Plant Nutrition Institute and the International Fertilizer Industry Association are encouraging the industry to promote the proper use of fertilizer products to minimize their environmental impact. Read More
Precision AgARA Organized Precision Forum Hits Capitol Hill
September 24, 2014
The Coalition for the Advancement of Precision Agriculture (CAPA) hosted its inaugural Precision Ag Forum, Sept. 18, in Washington, D.C. Read More
FertilizerFactors To Consider When Placing Fertilizer With Seed
September 24, 2014
The type of crop, fertilizer source, row spacing and soil environment all affect how much fertilizer can be safely applied with seed. Read More
FertilizerSidedressing Manure Into Corn Has Promising Results
September 24, 2014
Applying manure to growing crops can boost yields, reduce nutrient losses and give livestock producers another window of time to apply manure to farm fields. Read More
FertilizerWhen To Sample Manure For Analysis
September 24, 2014
Because the goal is to collect a sample that represents the manure actually being applied, the best time to sample is during loading or field application. Here's why. Read More
Syngenta
Seed/BiotechSyngenta Faces Second Lawsuit Over Agrisure Viptera Cor…
September 23, 2014
A second company has sued Syngenta AG over sales of genetically modified corn seed not approved by China. Read More
StewardshipCover Crops Field Guide For Farmers Expanded
September 23, 2014
Farmers interested in planting cover crops to improve soil health now have an updated and expanded resource in the second edition of the Midwest Cover Crops Field Guide. Read More
HerbicidesArysta LifeScience Launches Contest For Wheat Growers
September 23, 2014
The Flush after Flush Photo Finish contest encourages farmers across the U.S. to participate through Instagram or Twitter using the hashtag #FlushAfterFlush. Read More
FertilizerCF Industries Confirms Merger Of Equals Discussions Wit…
September 23, 2014
CF Industries Holdings, Inc. has confirmed that it is in preliminary discussions with Yara International regarding a potential merger of equals transaction. Read More
StewardshipProgram To Examine Ag-Related Practices, Policies To Pr…
September 22, 2014
A panel discussion on October 14 will include a significant discussion on key issues and solutions related to all aspects of harmful algal blooms. Read More