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Storms & Stewardship

Monday, February 1, 2010
filed under: Weeds

Growers across the country are accustomed to the uncertainty that comes with all the variables in producing crops. The tough weather of 2009 drove that home for sunflower growers in the Upper Midwest. Adding to the woes of weather is the ever-present pressure from tough weeds and diseases.

While no one can control the weather, there are ways to control the problems of weeds and diseases. The Clearfield® Production System knocks back the biggest threats, but resistant weeds are beginning to emerge. Protecting this important technology through good stewardship practices will ensure that resistant weeds and diseases stay out of sunflower fields for growers across the country.

‘Cold & Wet’ Creates Challenges

A late spring, cool summer and early frost created a serious set of challenges for Upper Midwest sunflower growers this past season. From start to finish, many growers have been obliged to shift their practices to accommodate the forces of nature.

Dr. Kirk Howatt has been a weed researcher in cereals and oilseed crops at North Dakota State University for 10 years. He counseled many growers struggling with timing the regular functions of growing and harvesting sunflowers in 2009. “Even my own plots were seven to 10 days late for planting this year,” Howatt notes. “Development lagged behind all season.”

With pockets of frost hitting the region after Labor Day, plants had no chance to dry down to the recommended 30 to 35% moisture for preharvest herbicide application. Late-season treatments were tough to fit in because of delayed development and weather, thus increasing disease and weed pressure.

“Diseases and weeds thrived after initial frosts, allowing continued inoculum and seed production,” Howatt says. “I had some growers [who] felt like the only thing that really grew this year was Sclerotinia. . . . The lack of those end-of-season glyphosate treatments could lead to a bumper crop of spring weeds.”

The Clearfield Advantage

Howatt has been impressed with the impact of the Clearfield Production System on sunflower in North Dakota. Clearfield plus a soil-applied component can manage early emerging weeds, making the window for postemergent applications both broader and more flexible.

“With larger flushes of weeds like we may well see in the coming year, the Clearfield portfolio of products is a big help,” he observes. “Not only does it provide good control of both broadleaf weeds and grasses, but the control can be achieved without losing marketability of nontransgenic varieties.”

Eastern North Dakota farmer Anthony Thilmony stopped growing sunflower in the late 1990s and early 2000s because eastern black nightshade and marsh elder clogged his fields, and his choices for control were few and far between. With the introduction of Clearfield sunflower, Thilmony found a solution to his growing weed problem.

“When Clearfield sunflower [hybrids] were introduced, I tried them the first year and was totally impressed with control of the two main weeds I’m worried about; and this allowed me to keep sunflower in our rotation,” Thilmony says.

A Historic Discovery & Beyond

The introduction of Clearfield sunflower provided growers with their first opportunity to control most broadleaf weeds with postemergent herbicide applications. As part of the Clearfield Production System, BASF Crop Protection introduced Beyond® herbicide, a member of the imidazolinone chemical family and an ALS inhibitor.

When Beyond herbicide is applied to Clearfield sunflower at the two- to four-leaf stage, growers see both contact and residual activity on broadleaf weeds and grasses, including kochia, marsh elder, cocklebur, Canada thistle, foxtail, volunteer cereals and non-Clearfield wild or volunteer sunflower. Beyond is labeled for use up to the eight-leaf stage, but performance is best when applied at the earlier stage.

Beyond also works well in no-till settings, which may be increasingly important after delayed seasons like 2009. Applications of Beyond may help growers get control of weeds and grasses that would otherwise survive because they were not tilled under preplant.

Because it is a highly effective system for controlling a wide variety of weeds, resistance to ALS inhibitors looms large as a threat to crops. Researchers have already found populations of kochia, pigweed, marsh elder and nightshade in North Dakota that are resistant to ALS inhibitors. To keep this problem from spreading, today’s growers must practice technology stewardship to ensure that the benefits of the Clearfield Production System are available for generations to come.

Clearfield Sunflower Stewardship

If wild sunflower and other weeds become herbicide-tolerant, the effectiveness of these technologies for weed control will diminish. That’s why growers using the Clearfield Production System need to be vigilant about responsible use of the products. Good stewardship practices range from crop rotation to the use of non-ALS chemistries for herbicide resistance management.

The following are best practices for Clearfield sunflower stewardship:

• Always grow Clearfield sunflower in rotation with other non-Clearfield crops, such as wheat, corn or sunflower. Rotating crops breaks the cycle of continuous sunflower production and allows for use of alternative mode-of-action chemistries and different tillage options.

• Use alternative (non-ALS) mode-of-action herbicides such as a growth regulator or photosynthesis inhibitor with activity on sunflower in the rotational crop. The alternative mode-of-action helps control volunteer Clearfield sunflower and other ALS-resistant weeds. It also reduces the selection pressure of ALS-inhibiting herbicides from continuous dependence on the chemistry.

• Limit the sole reliance on ALS herbicides to no more than two out of four years in the same field. Whenever possible, use sequential herbicides or tank-mix partners with multiple modes-of-action on targeted weed species in the sunflower crop and in rotational crops.

• Do not plant Clearfield sunflower on land with a history of heavy wild sunflower pressure. This helps reduce the threat of outcrossing Clearfield sunflower with wild sunflower.

• Control emerged wild sunflower in the field prior to planting Clearfield sunflower by using non-ALS burndown herbicides on no-till or minimum-till fields, or by tillage in conventional-till fields. Spraying glyphosate prior to planting eliminates any wild sunflower in the area that may be resistant to ALS-inhibiting herbicides, while also reducing the reliance on ALS herbicides in controlling wild sunflower.

• Spray a preplant or preemergence herbicide earlier in the season, prior to spraying Beyond herbicide. A soil-applied grass herbicide like Prowl® H2O can be used before spraying Beyond to increase weed control on targeted weed species and add another mode-of-action to the sunflower program to help prevent herbicide-tolerant weeds.

NDSU’s Kirk Howatt continues to evaluate Clearfield seed varieties that will allow for improved control of troublesome weeds with Beyond. But until that time, he urges Clearfield sunflower growers to incorporate stewardship practices to keep weed populations low and herbicide efficacy high.

“We can’t control the weather,” Howatt notes. “So we have to control the way we use the trait.”

Ryan Bond and Chris Wharam, technical market manager and technical service representative, respectively, for BASF Crop Protection, contributed information for this article.

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