Weedmanagementonthemindsofs.cfm Weed management on the minds of soybean farmers
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Weed management on the minds of soybean farmers

"Because glyphosate herbicides have been used so much, it has led to some problems with weed resistance. Five years ago glyphosate herbicide worked for everyone and now that isn't always the case," said Bryan Young, Southern Illinois University associate professor of plant, soil and agricultural systems.

By Jennifer Bremer

The threat of glyphosate-resistant weeds continues to be on the minds of soybean farmers across the country.

Continual changes in cropping systems is something today's farmers deal with much easier than the farmers of yesteryear. While many farmers in the Midwest have had to deal with glyphosate-resistant weeds, northeast Iowa farmer Greg Alber has not experienced these problems with weeds in his soybean fields yet.

"We haven't had any glyphosate resistance yet. We have used a burn down and then one pass of glyphosate herbicide system for over 10 years," he explained. "It works great for us."

Southern Illinois University associate professor of plant, soil and agricultural systems Bryan Young said weeds have mostly been managed through glyphosate dominant systems since 1998. "The only other technique that worked to near the same success in weed management was cultivation," he said.

While glyphosate systems continue to be the main tool in weed management, Young said many farmers are having to come up with a new mode of action as weeds become glyphosate resistant.

"Because glyphosate herbicides have been used so much, it has led to some problems with weed resistance," he said. "Five years ago glyphosate herbicide worked for everyone and now that isn't always the case."

Young advises farmers to have a more diverse system and be ready to use something different in order to limit resistance.


With no-till production becoming more popular in recent years, farmers have had to rely more heavily on herbicides to kill out weeds before they start to grow.

Alber has used no-till for all of his 650 acres of beans in Buchanan County since 1993. "The burn down becomes very important prior to planting. Then we generally don't have to apply the glyphosate herbicide until about July 4," he explained.

He has been pleased with this system, as it gives him a window of time to get other things done before needing to spray again; and he has always gotten good weed protection with this system.

"July is the driest month, with slow weed growth, so anything that is growing at that point is then killed by the one-pass spray and it also seems to prevent further weed growth," he said.

No-till has been an important part of his farming operation because of the energy and time savings. Alber said he saves money on fuel and equipment, while also preventing erosion and being a good conservationist.

Scouting crops for pest and weed problems is a daily occurrence at his farm. With aggressive scouting, he has been able to protect his crops from major problems.

Young agreed no-till production has led to better equipment and seed technologies to help farmers save money.

Weed management

"Weed management is the number one issue with growers and it seems to be more of a problem in soybeans," said Young. "We need to diversify how we control weeds, especially because of the new resistance."

Young said the number one weed problem for soybean producers in the eastern Corn Belt states is marestail. Over 5 million acres have problems with marestail and some marestail is even becoming glyphosate resistant.

"Waterhemp seems to be the number one weed problem in Iowa, Missouri and Illinois," said Young. "Glyphosate-resistant waterhemp has been found in Illinois, Missouri, Kansas, Minnesota and Texas, which makes controlling it more challenging."

He said the glyphosate-resistant waterhemp does not seem to be an isolated issue, rather a rapidly spreading issue that is expected to be found in more soybean producing states.

"Once we see the problem, then it is important to find a reactive solution," he added.

Alber said his number one weed problem is giant ragweed. While he hasn't seen problems with glyphosate-resistant ragweed, Young said the resistance is becoming widespread throughout most soybean regions.

Application timing

Young said incorrect herbicide application timing is the main problem farmers have when weeds are not controlled properly.

"Farmers need to make herbicide applications sooner, when weeds are smaller, in order to gain better control," he said. "This often takes regular scouting in order to stay on top of the problem."

Besides timing, knowing which herbicide to use is important, as well. Continual advancements in technologies with new soybean seed traits causes management to continue to change, also. Young suggests using residual herbicides ahead of new systems to help with the tough-to-manage weeds.

"If weeds are controlled before they are beyond 4 inches in height, they are easier to manage," he said. "Problems have to be dealt with differently if glyphosate resistance is not discovered soon enough."

Young said the best way to control weeds is always through a program approach and, if a glyphosate program won't work because of resistance, then farmers should seek help from a professional, regarding weed management.

"Start with a clean and effective burn down program, use strong residual herbicides and be sure to apply herbicides at the proper time," he said. "By following a good system, weeds should not be an issue when it comes to soybean yields."

Even though Alber hasn't had problems with glyphosate-resistant weeds, he does realize that the time will come in the near future when he will have to learn how to manage those weed issues in order to continue to raise soybeans that yield more than 50 bushels per acre.

Jennifer Bremer can be reached by phone at 515-833-2120 or by e-mail at jbremer@hpj.com.

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