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Battling Stubborn Weeds

Tue, Mar 19th, 2013
Posted in All Agriculture

Herbicide-Resistant Weeds in Minnesota and What You Need to Know

Farmers battle weeds in their fields every year. With the introduction of new herbicides and other tools to the market in the last 20 years, many farmers believed they had the weapons they needed to fight these unwanted plants.

But the weeds are doing what they always do—adapting and fighting back.

It turns out weeds have weapons of their own, including the ability to become resistant to a variety of herbicides. Herbicide-resistant weeds are not a new phenomenon. Weeds and other pests have always adapted to the ever-changing environment. These cases of herbicide resistance, though, were often more isolated and on a smaller scale than what many farmers face today.

The Minnesota Soybean Growers Association is holding a series of free seminars around Minnesota to help farmers learn more about weed resistance issues and to help them create a plan for their farm. Called Profitability Optimization Dialog (POD) seminars, these events bring university researchers and industry experts together with farmers for awareness and education.

The seminars will feature University of Minnesota weed researcher Dr. Jeffrey Gunsolus as well as University of Tennessee weed scientist Dr. Larry Steckel. Steckel will discuss the significant challenges farmers from Tennessee and other states are facing when it comes to herbicide resistant weeds.

“We know there are issues emerging in Minnesota and the Dakota’s, and farmers in other parts of the country are dealing with pretty substantial problems,” says Kurt Krueger, a farmer from Rothsay, Minnesota and Minnesota Soybean Growers Association director. “We want to get on top of this issue here so that it doesn’t become a bigger issue.”

Three POD seminars are scheduled for late March. Dates and locations include:

March 26

Mahnomen, MN

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March 27

Willmar, MN

Holiday Inn Convention C enter

March 28

North Mankato, MN

Best Western Hotel

All events run from 8:30 a.m. to 3:00 p.m. with registration beginning at 7:30 a.m. The afternoon will focus on grain handling and technology. The seminars are free and lunch is provided. Please RSVP to the Minnesota Soybean office at 888-896-9678 or register on-line at www.mnsoybean.org.

Though many think of herbicide resistance as an issue limited to southern states, these weeds have made their way to Minnesota as well. Farmers within the state typically deal with three types of resistant weeds: water hemp, giant ragweed and common ragweed.

Even if a farmer has not yet experienced this issue, herbicide-resistant weeds can spread very rapidly.

“Many farmers think they will be able to catch the weeds and treat them before they get out of hand,” said Jeffrey Gunsolus, University of Minnesota professor and extension weed specialis . “However, weeds spread very quickly, often exponentially. If the weeds are missed for even one or two years, they become more established and much more difficult to deal with.”

“There’s a growing awareness of weed resistance among the farmers I talk with,” said Rothsay, Minnesota farmer Kurt Krueger. “We’re recognizing the need to have a diversified treatment approach.”

A lack of diversification in weed-control techniques takes some of the blame for the growth of resistant weeds around the country. Some herbicides, such as glyphosate, give farmers the ability to fight weeds with one strike. Glyphosate can also be used year after year on a variety of crops, giving weeds a better chance of developing resistance.

The spread of resistant weeds across the country is troubling for farmers and others in the ag industry.

Gunsolus encourages farmers to think of their weed-control options as tools in a tool box, and herbicide-resistant weeds remove some of those tools. Ultimately, diversification is the key, he said. Instead of focusing on one method of pest control, it is important for farmers to use a variety of agronomic principles to best protect their crops.

He recommends starting with a pre-emergence herbicide. Applying herbicide at the time of planting introduces new chemistry to the soil right away and will help reduce weed density. Hindering weed growth from the beginning gives the crop a better chance to establish itself without fighting the weeds for nutrients. The crop itself can then help reduce weed growth, as the crop canopy will prevent the weeds from receiving sunlight. “Shading is free weed control,” said Gunsolus.

Pre-emergence herbicide will make a post-emergence herbicide more effective because growth of the weeds will be delayed. This will give the farmer a larger window to spray the weeds when they are smaller and more susceptible to herbicides. Gunsolus estimates that approximately 30 percent of Minnesota farmers used pre-emergence herbicide in the 2012 growing season but he expects that number to increase in future years.

Farmers must also rotate, not only with crops but with weed-management techniques as well. Introducing new crops into the rotation, like alfalfa, is also a good idea, said Gunsolus.

Gunsolus encourages patience when trying different weed-management options. “Farmers may not see immediate gains when using a variety of techniques but they will see improved conditions in the longer term,” he said.

For now, the next step in the fight against resistant weeds is education. Get to know your weeds before they find you. Learn to identify them and the methods that can be used in combination to hinder their growth. Otherwise, by the time a farmer finds a resistant weed in his or her field it may be too late.

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