Corn Growers Need Multifaceted Plan to Control Weed Resistance

Weed resistance is creeping across the Corn Belt, making it essential for growers to continually evaluate their weed control needs. From learning about the latest herbicide technologies to closely monitoring fields for unexpected breakouts, staying ahead of resistant weeds can feel like a full-time job.

Fortunately, the right weed-management strategy can lift much of the burden off of growers’ shoulders, helping them save time, money and worry. But to find the best management solution, they must first understand the problem weeds in their fields.

Getting to Know Tough Weeds

Broadleaf weeds like giant ragweed, waterhemp and Palmer amaranth continue to make headlines as they invade cornfields and reduce yields. Each weed has its own story, including the reasons why it’s so difficult to control.

Giant ragweed can germinate deep in the soil and emerge below the treated zone in the soil profile. Waterhemp and Palmer amaranth, both species of pigweed, can deposit up to 1 million seeds per plant into the soil. As a result, weed populations can increase rapidly and take over crops, thereby reducing yields.

But these species aren’t the only yield-robbing weeds plaguing growers’ fields. For example, marestail, one of the first glyphosate-resistant weeds identified in U.S. row crops, produces seeds that can be transported by wind, which results in the weed spreading rapidly. Morningglory seeds, on the other hand, have extremely hard coats, allowing them to remain viable in the soil for more than 50 years.

The Dangers of Maintaining the Status Quo

Tough weeds, combined with reduced tillage programs that growers have adopted to sustain their soil, put a lot of pressure on herbicides to deliver effective, complete control. But overusing these same herbicides without a programmed approach may eventually lead to resistance, which oftentimes isn’t easy to detect in the early stages of development.

"It’s important for growers to always monitor their weed-management practices, because subtle weed escapes in a field can be a signal that there may be resistant weeds emerging," says Dane Bowers, Syngenta technical product lead.

While a few escaped weeds won’t cause significant problems initially, the plants continue to produce seeds each year, Bowers points out. "In the second year, those plants become more visible; and by year three, the grower will have a major issue," he says. "Escaped weeds produce seed, contributing to the weed seed bank and leading to a long-term weed control problem for growers."

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Taking a Proactive Approach

Even though glyphosate resistance is expanding, managing resistant weeds in corn is achievable when growers, such as Philip Nelson in Windom, Kansas, are proactive about their weed-management strategy. "Pigweeds have greatly affected our herbicide choices," Nelson says. "In fact, we now apply herbicides ahead of time to keep the weeds from growing. It’s getting really hard to kill a pigweed at any stage of growth, but you can still kill the sprout and keep it from becoming a problem."

"It’s important for growers to always monitor their weed-management practices, because subtle weed escapes in a field can be a signal that there may be resistant weeds emerging."

The need to control tough weeds is one reason growers use a powerhouse product like Acuron^® brand herbicide. First introduced to growers in 2015, Acuron contains three effective modes of action and four active ingredients, including a new chemistry at the time of its launch—bicyclopyrone. Together, these ingredients work together to control weeds before they emerge.

"My toughest weed to control is giant ragweed," says Ken Kurtenbach, a corn grower from Lindsay, Nebraska. "It grows fast, is mostly glyphosate-resistant and just gets out of hand with no-till. Acuron has performed exceptionally well on giant ragweed. There is absolutely no comparison between Acuron and other things I have applied before."

Independent research trials also show a clear Acuron advantage. In six 2015 university trials across four different states, Acuron consistently outperformed other competitive herbicide products. "We saw a notable yield advantage over competitive herbicides in these trials, including SureStart^®, Verdict^® and Corvus^®," says Gordon Vail, Ph.D., Syngenta technical product lead. "While we’re still finalizing the results of 2016 trials and on-farm use, the weed control from Acuron continues to be best in class."^*

Becoming More Flexible

In 2016, Syngenta introduced Acuron Flexi herbicide to give growers effective weed control with added flexibility. With three active ingredients, including bicyclopyrone, and two effective modes of action, Acuron Flexi delivers a multitargeted approach to weed control. Although Acuron Flexi doesn’t contain atrazine or glyphosate, it can be tank mixed with these herbicides, making it a valuable solution for growers whose use of atrazine is limited.

"I use Acuron Flexi in areas where I cannot use atrazine," says Tony Bomkamp, a grower whose farm is located along the Lower Wisconsin Riverway, where the use of atrazine is prohibited. "It has done a wonderful job controlling weeds, especially giant ragweed. Acuron Flexi keeps all the weeds out of my fields, and I only have to apply it one time."

Managing tough weeds is a dynamic problem that’s always shifting and evolving. Weeds continue to invade non-native areas, developing resistance to different herbicides along the way. Fortunately, companies like Syngenta are developing the tools and technologies that can help growers manage problem weeds.

"Globally, Syngenta invests $4 million every day in research geared to solve growers’ toughest challenges," Vail says. "Weed resistance is certainly one of those challenges that we, along with our reseller partners in the field, will continue to help growers manage."

*Trial Information: Locations—Rowher, Arizona; Ames, Iowa; Dekalb, Illinois; Perry, Illinois; Rochester, Minnesota; Waseca, Minnesota. Universities involved—University of Arkansas, Iowa State University, University of Illinois and University of Minnesota. Plot size—minimum of 10 feet by 30 feet. Application rates and timing—Acuron @ 2.5 to 3 qt/A, Surestart II @ 1 to1.5 qt/A, Verdict @ 16 to 18 oz/A and Corvus @ 5.6 oz/A as pre-emergence herbicides with or without atrazine. Weeds present—ivyleaf, morningglory, cocklebur, common and giant ragweed, common lambsquarters, and giant foxtail.