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You Are Here Sunflower Magazine > Herbicide-Tolerant Hybrids’ Big Impact


Sunflower Magazine

Herbicide-Tolerant Hybrids’ Big Impact
April 2012

The advent of the Clearfield® production system in 2003, together with the entrance of ExpressSun® hybrids in 2007, promised to be the latest and greatest in sunflower growers’ ongoing battle in weed control. Some sunflower breeders speculate the technology eventually will be present in all new domestic market hybrids.

The technology likely helped save acres that would otherwise have been lost due to pesky broadleaf weed problems and utter frustration on the part of the grower. “We were in danger of losing major portions of the sunflower production regions that were backing out of sunflower because of no weed protection,” observes Bruce Due, agronomist with Mycogen Seeds, whose company has offered Clearfield hybrids since the technology became available. “Growers were simply having too great of yield loss and harvest problems due to the weed issues.”

Kent McKay, BASF technical service representative, could not agree more.

National Sunflower Association crop surveys indicated that common cocklebur, marshelder and wild sunflower were causing major issues in both oil and confection sunflower fields. “Having the Clearfield technology definitely has helped keep these significant weed problems controlled — and it shows in not only yield, but in seed quality” says McKay.

Due says it was about having options that weren’t there before. Clearfield hit the market and offered an avenue for post-emergent weed control and flexibility — not only at preplant, but to go in afterward to control those later-emerging problems. Growers would no longer be losing yield to overpowering weeds.

“The ExpressSun market share has grown every year since the introduction in 2007-2008,” notes Bob Weigelt of DuPont. “A number of growers tell me they would not be growing sunflower if they did not have ExpressSun technology.”

Whether the grower uses Clearfield or ExpressSun hybrids, with all new technology, there is a learning curve. As with any new tool, it needs to be understood and used appropriately to be effective and reduce herbicide resistance problems. Many recommendations surrounding these technologies have been discussed in previous articles in The Sunflower. Yet even after several seasons and countless acres utilizing the relatively new technology, there are still issues worth examining.

Mother Nature always adapts. The herbicide-tolerant hybrid is a tool — not a complete weed control program in and of itself. Nature tends to find ways to overcome. It’s important to use these herbicide-tolerant hybrids and their companion herbicides in combination with other herbicide modes of action and/or cultural methods like crop rotation and even occasional tillage. Protecting this important technology through good stewardship practices will ensure that resistant weeds and diseases stay out of sunflower fields for growers across the county.

• Be mindful of resistant weeds. Kochia, at one time almost completely controlled, continues to be the main ALS-resistant weed problem throughout the sunflower-producing geography. Using a “pre” product like sulfentrazone and/or utilization of glyphosate in a burndown pass should always be done as part of the overall system. When it comes to kochia and other troubling weeds, there always needs to be a “Plan B.”

It can get tricky when it comes to ALS chemistries like the imidazolinones and sulfonylureas. Some kochia is susceptible to both, some is resistant to IMIs but not SUs, some is resistant to SUs but not IMIs, and some is resistant to both.

North Dakota State University weed scientist Kirk Howatt says it’s important for each farmer to be aware of his own weed populations — and which ones have developed resistance. “In North Dakota especially, you can pretty much expect at least some of the plants in a field to have ALS resistance,” Howatt notes. “That’s why it is crucial to incorporate multiple methods of control, such as some form of tillage or applying a soil residual product with the preplant burndown.” This mindset extends beyond the sunflower season. Attack these difficult weed problems in a given field in the years before sunflower is grown there.

• Keep a close eye on wild sunflower. Mycogen’s Due says the technology is working right now; but he’s concerned about its longevity when considering wild sunflower as a major threat. “Wild sunflower may be an alarm waiting to go off,” he says. “I see it in so many areas where it starts out small and then quickly becomes a serious problem.”

Due and others in the weed science community know that because nature always wins over in the end, the herbicide-resistance technology is at risk. Even if wild sunflower appears to be mild or confined to the perimeter of a field, it should be dealt with in a timely manner. All it takes is for adjacent wild sunflower to bloom and pollinate at the same time as the commercial field for the risk of cross-pollination to become a very serious problem. The same would hold true for volunteer sunflower.

Howatt adds that while wild sunflower may not be a large weed issue in North Dakota, it is more of an issue in Kansas, Nebraska and parts of South Dakota. So, growers in different production regions need to be mindful of the “problem weeds” in their particular area.

• Total control may not be possible. A sunflower grower can now keep certain weeds at bay for the growing season, while greatly reducing weed seed production and the spreading of a problem weed. Total control, though, needs to be kept in perspective as part of a multi-year program approach, utilizing materials like glyphosate and clopyralid in rotation crops. The herbicide-tolerant hybrid system can certainly be beneficial as part of the overall goal of weed population reduction, while still being able to produce a profitable crop like sunflower.

Howatt says diversity helps preserve the available weed control tools in Clearfield and ExpressSun technology. Weed resistance to ALS and glyphosate herbicides typically develops independently, so rotation of crops with different herbicide-resistance technology could help break up the cycle of weed resistance. “To preserve the longevity of the technology behind herbicide-resistant crops, whether it’s ALS or glyphosate, the key is to combine modes of action on your overall herbicide plan.” So take advantage of all weed control tools, whether they be seed technology, herbicide, tillage or cultural in nature, he says.

Grower Perspectives

South central North Dakota grower John McCrory offers a unique perspective since he plants half of his 1,500 acres of high-oleics into ExpressSun and the other half with Clearfield varieties. He says the herbicide-tolerant hybrids have allowed him the option of going in to get those weeds (e.g., kochia and marshelder) that pop up mid-season and compete with the sunflower. The technology also provides better-than-expected control of the pesky cocklebur. “The benefits of this technology greatly outweigh any drawbacks if there were any — and we haven’t found any yet,” McCrory affirms.

Go a little further south to Chad Vander Vorst’s farm near Strasburg, N.D., where they saw their best ’flowers in years in 2011. He eased into ExpressSun hybrids starting in 2009 with about half of his crop. That increased to three-fourths of his acreage in 2010. The way the system addressed the Canada thistle problems convinced Vander Vorst to go 100% ExpressSun in 2011 on his roughly 1,200 acres. What sealed the deal was when the newer ExpressSun hybrids also came with downy mildew resistance, making them the “total package” to meet his needs.

Growers pay close attention to the weed history of their fields in order to tackle the known problems. Gary Knell, who farms near Hazen, N.D., switched to ExpressSun hybrids three years ago. Areas where he would classify as “problem fields,” he deals with kochia, buckwheat and a variety of broadleaf weeds. “Our first concern was a possible yield drag with the new technology. But it’s not a problem. We use it as our ‘insurance policy,’ ” Knell remarks. “We like the option for mid-season application to take out the late-emerging kochia.”

Northwestern North Dakota grower Charlie Sorenson now plants all 500 of his oil sunflower acres using the ExpressSun technology. Back in 2009 he planted half his acreage with ExpressSun hybrids, hoping to see results — especially in dealing with kochia. “I used it on ground that I normally wouldn’t grow sunflower on because of the weed history,” Sorenson says. “We had kochia problems that [were] increasing on certain fields. Now, we no longer have to worry about those fields.” He adds that wild sunflower has also been kept at bay and he’ll continue to use the ExpressSun hybrids as a “sort of insurance policy.”

Tom Bargen, who farms in southeastern Nebraska, has been growing sunflower for more than 20 years. His operation has been strictly no-till since the late 1980s, and he grows only non-GMO crops. So his weed management needs are somewhat complex. Bargen manages his weed issues with Clearfield hybrids. He also notes an added bonus with Clearfield — one which may not be based in science, but rather with observation on his acres: less pressure from the Dectes (longhorned beetle) insect. “We don’t really know why,” Bargen says. “What might be happening is that with fewer weeds, we have less host plants for the pesky bugs.”

Growers in varied regions benefit from the technology that tackles a broad range of weeds. Ron Meyer, Colorado State University extension agronomist based in Burlington, says that both the Clearfield and ExpressSun technologies have made a significant impact in the High Plains.

Many things in agriculture cannot be controlled, but growers must control the way they use this trait in order to preserve its integrity and efficacy. As these technologies continue to evolve, the grower should continue to benefit from companies offering new, fine-tuned ExpressSun and Clearfield varieties available for planting each season.

— Sonia Mullally

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