Ready to Resist

insect-, herbicide- and disease-tolerant crops
What would you do with one silver bullet that allowed complete control over a single pest that plagues your fields? Would you use it against insects, weeds, diseases or nematodes? See the Farm Journal Pulse results at right to learn what your fellow farmers said. While silver bullets are hard to come by, there are other resilient options you can load in the chamber against pests.

Billions of dollars are spent on corn and soybean breeding research each year to address the worst pests. Because of this research, insect-, herbicide- and disease-tolerant crops save millions of bushels annually. However, nature is constantly at work to stay one step ahead of scientists, and as soon as a new solution is found researchers work diligently to preserve it and find additional solutions before resistance evolves. Learn more in the following pages about the research underway to outsmart pests today and what’s coming in the future.

Farm Journal Pulse

 

 

 

 

 

 

 

 

 

 

 

 

 

Former “Billion-Dollar Bug” is Mounting a Comeback

Prior to Bt technologies farmers lost $1 billion annually to corn rootworm (CRW)—in the form of chemical costs or actual yield loss. That’s $11 per acre based on USDA’s recent 89.1-million-acre count. With resistance developing to traits that once killed the pest, it might just nibble its way back to a billion-dollar price tag.

“Back in the day, CRW control was unbelievable,” says Tim Reinhart, corn and soybean farmer in Champaign, Ill. “We’re seeing more pockets where we should have complete control and don’t—it’s concerning.”

CRW poses a double threat: The adult snips corn silks and, if unchecked, could prevent successful pollination and kernel development. The larvae munch on roots, which leads to risk for disease and plant stress. With resistance on the rise, it’s time to find a solution.

“The first documented case [of CRW resistance] was reported in Iowa in 2011 to Cry3Bb1 [corn rootworm I],” says Dalton Ludwick, post-doctoral researcher at Virginia Tech who works with USDA. “Now we have documented issues in Iowa, Illinois, Minnesota, Nebraska and North Dakota.”

Researchers suspect resistance has spread to other states and just hasn’t been formally documented yet. The first case of resistance was actually discovered in 2009 but took two years of research to confirm.

“Typically, if we see resistance it’s because the same trait has been used year after year, such as in northeast Iowa where it was first detected,” says Marlin Rice, Syngenta product biology technical manager. “Rotating to another trait or crop helps break that cycle, which greatly diminishes the risk of resistance.”

In lab studies, researchers proved it only takes up to four years of pressure to select for CRW resistance on three of the four proteins on the market. When the pest develops resistance to a protein, the Bt technology within a specific hybrid can be rendered ineffective or crippled.

“All available hybrids with pyramided traits for CRW use either Cry3Bb1 [Monsanto] or mCry3A [Syngenta] in combination with a second toxin, either Cry34/35Ab1 [Pioneer and Dow AgroSciences] or eCry3.1Ab [Syngenta],” says Joseph Spencer, insect behaviorist at the Illinois Natural History Survey at the University of Illinois. “This means where resistance is present in the population, there might be at best only one effective toxin at work.”

There are essentially only two modes of action used in the four proteins. The Cry3Bb1, mCry3A and eCry3.1Ab represent one mode of action and display the greatest amount of resistance, according to Ludwick. The Cry34/35Ab1 protein took longer to show resistance in lab testing.

“The Cry34/35Ab1 [Herculex] is a unique protein complex; it’s a combo of two proteins that work together inside the insect,” says Clint Pilcher, Corteva Agriscience integrated solutions manager. “This dual protein complex may lend itself to being more durable than other CRW proteins.”

Monsanto is poised to release SmartStax Pro with a third mode of action. The company partnered with Corteva Agriscience so the trait can be developed in its corn lines as well.

“We’re still waiting for a couple regulatory approvals,” says Tom Clark, Monsanto global insect trait platform lead, corn and soy technology. “We can’t give an exact date but our plan is to hopefully launch within a couple of years. We don’t expect this to be our final CRW product; we’ll continue to research solutions.”
The new trait, Corn Rootworm III, is formally referred to as MON87411. Monsanto is using RNAi technology to create this trait, which includes Cry3Bb1 and glyphosate tolerance, and is doing resistance testing before launch, per the norm for new traits.

University of Illinois researchers are also investigating the promise of two naturally-occurring resistance genes in corn. One interacts with nematodes in the soil and tells them to attack the rootworm larvae. The other is related to the plant’s ascorbate synthesis pathway that produces free radicals that injure feeding insects.

“We were screening [corn lines] for insect resistance. There were not many, but we found some,” says Martin Bohn, corn breeder in the Department of Crop Sciences at the University of Illinois. “We had to look into lines from Argentina, Brazil and the Caribbean Islands to find it.”

Until alternate forms of resistance come to the market, farmers will have to use tried-and-true methods to manage the pest.

“Crop rotation is the best option. If you can’t rotate, plant something with two modes of action. If you can’t do that, use a single mode of action and a soil-applied insecticide—that’s the bare minimum,” Ludwick says. “If you can’t do that, and have CRW present, you’re out of luck.”

Reinhart keeps resistance manage-ment top of mind. “We use SmartStax on our corn-on-corn acres and are ready with insecticides if we see a lot of beetles,” he says.

While only five states have officially documented resistance, it’s likely present in other states. Since it only takes up to four years of pressure for the pest to become resistant to most of the proteins, the rest of the U.S. is a ticking time bomb.

Not All Bt Traits Offer the Same Control

Corn rootworm (CRW) isn’t the only pest that demands control. Prior to CRW resistance, corn borer control came in the form of a Bt trait in 1996.

“I think with corn rootworm traits, the initial expectation was that the traits would blow corn rootworm out of the soil because of what we saw with European corn borer—the first Bt trait,” says Marlin Rice, Syngenta product biology technical manager. “The European corn borer trait was the silver bullet, a high dose trait, and after more than 20 years it has no documented resistance.”

Alternatively, CRW traits are low-dose traits. This means you’ll occasionally have survival or unexpected injury from large populations of the pest.
Both traits—CRW and corn borer—were created using biotech. Bt stands for Bacillus Thuringiensis, a bacterium found in the soil with natural insecticidal properties. There are hundreds of strains of Bt.

“We identify Bt proteins that are very specific to certain insects, isolate that gene and insert it into the corn genome,” says Clint Pilcher, integrated solutions manager, Corteva Agriscience.

 

EPA designated “red zone” is  at risk for developing Bt resistant populations of corn rootworm.

Soybean Weed Control Starts with the Seed

In 1996, Roundup Ready soybeans revolutionized the way you could farm. Weed issues became virtually non-existent, herbicide programs were cheaper and yields soared. But all good things come to an end and glyphosate resistance finally emerged, bringing with it yield loss, more expensive herbicide bills and weedy, ugly fields.

As new and growing weed resistance looms, it’s important to know your options, especially in soybeans. While herbicide-tolerant trait packages have revolutionized farming in the past, their benefits can quickly fade with improper use.

Today’s weed control options in soybeans include: Roundup Ready 2 Yield soybeans, Roundup Ready 2 Xtend soybeans and LibertyLink soybeans. New products pending approvals are Enlist E3 soybeans, GT27 soybeans and MGI soybeans.

“The most driving weed control needs are on the soybean side because we have so many herbicide options in corn,” explains Duane Martin, Syngenta commercial traits manager. Think about it, waterhemp, marestail, Palmer amaranth are all broadleaf weeds, and broadleaf herbicides have always been available in corn.

“I planted 100% corn this year just to avoid dealing with the headache of weeds in soybeans,” Reinhart says. “We’re going to try one of the new soybean traits next year to use chemicals that have been fabulous in corn.”

While research is underway to find new herbicide modes of action that could be accompanied with a trait, they are years from commercialization—if ever found. With that in mind, it’s critical to protect traits and herbicides so they last as long as possible.

Start with the seed decision. “Growers need to consider their weed problems when selecting herbicide-tolerant seed,” says Rex Liebl, BASF global product development, herbicides. “When you look at the principles of integrated weed management, one of the most important elements is to mix or rotate modes of action, so you’ll have the option to use something different the second year on your troublesome weeds.”

Overuse of a small handful of herbicides, or a single herbicide, increases risk of resistance. For example, if you use glyphosate in soybeans and again in corn, you could be giving resistance a foothold in your fields.

“It’s all about how you put a weed control plan together,” says Arlene Cotie, Bayer senior development manager. “It’s the herbicide use pattern that creates herbicide-resistant weeds, not the traits.”

Resistance has been around since the 1960s, long before the invention of any kind of herbicide tolerance or native or biotech traits.

“I’m younger than some of these herbicides, but not by much,” says Mark Dahmer, Corteva Agriscience technical portfolio strategy leader. “I wish I could tell you how long the current and upcoming chemistries will last but we just can’t. The real issue is how we manage each field, each weed and any escapes. That is what will determine the herbicide, and herbicide trait’s, durability.”

 

More Options With Herbicide Tolerance

Breeding Pushes Disease Tolerance Envelope

Breeding advances brought an era of advanced disease control. The future of disease tolerance will use advanced breeding with targeted approaches that help maximize corn and soybean yield potential.

“The top five diseases in corn we focus on are anthracnose stalk rot, gray leaf spot, Northern corn leaf blight, Goss’s wilt and Southern rust,” says Jared Webb, DeKalb product development manager.

In soybeans, breeders focus on: white mold, phytophthora, sudden death syndrome and frogeye leaf spot.

“Disease tolerance is something we pay close attention to and select for,” says Shane Meis, Wyffels Hybrids director of research. “But we have to make sure yield isn’t sacrificed for disease tolerance. That perfect mix is the genetics that maintain high yield and have disease tolerance.”

Corn and soybean breeding advances result in a 1% to 2% yield gain each year—and at least part of that can be attributed to enhanced disease tolerance. While there still is a considerable number of crosses performed at random and then evaluated for performance, molecular markers, double haploid breeding and advanced gene editing speed the process at which advances are made and go to market.

“Today we still do traditional testing, but we really look at it from a molecular level,” says Kevin Cavanaugh, Beck’s Hybrids director of research. “We use molecular markers that are associated with resistance to certain diseases to screen parent lines. Most corn breeding programs use marker programs.”

Say you live in an area with high risk for gray leaf spot, researchers can use what they know about the corn genome to see if an inbred (single parent line) has natural resistance. If it does, and they’re breeding for your geography, they’ll keep that parent in the mix to make sure you have a certain level of disease resistance.

“One thing that’s really helped to identify and maintain resistance is double haploid breeding,” Meis says. “We’re testing with something that is fully inbred, genetically fixed, which means resistance will definitely occur in subsequent generations.”

Traditional breeding can identify resistance but lose it the following generation during the inbreeding process because resistance wasn’t genetically fixed. Double haploids don’t change from one generation to the next, so resistance will be present in the plant every time.

Finally, the most futuristic of breeding possibilities, gene editing programs such as CRISPR, could help bring products to market faster and with fewer regulatory hurdles. This technology allows researchers to make quick, efficient, GMO or non-GMO (depending on their goal) changes to the genome. It essentially involves inserting desirable or deleting undesirable parts of the genome.

“There are so many possibilities in gene editing, and we’re trying to leverage those,” Webb says. “The breeding cycle can take up to eight years though, so we have a few years before we’ll see the fruits of those efforts.”

As a result, traditional breeding for disease tolerance is still important. “We do 950,000 genetically unique soybean line tests each year because you have to look at a large number to see the best yield advances,” says David Thompson, Stine Seed national marketing and sales director. “With that number of products you’ll find solutions for diseases and other issues, without sacrificing yield potential.”

As disease tolerance improves, yield potential will only increase. Take a look at each of your fields and select hybrids or varieties that fit your disease pressure to maximize yield, while minimizing some of the need for added costs such as fungicide.

 

New Soybean Traits Gain Ground

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