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2010 weed watch

By Staff | May 28, 2010

Common lambsquarter.

By KRISS NELSON/Farm News staff writer

The era of using glyphosate alone to tackle weed problems is becoming a thing of the past, as more weeds are starting to show tolerance to the herbicide.

“We’ve been spoiled by some herbicides and it’s time to start paying more attention to what is out there,” said Bob Hartzler, professor of agronomy and Iowa State University Extension weed specialist.

Hartzler said growers are on the edge where glyphosate-resistant weeds will be showing up on more acres and, unfortunately, the easy days of weed control with just a few simple applications of a glyphosate are close to over.

Hartzler said waterhemp and giant ragweed are just a few of the weeds producers should be on the lookout for due to them having been officially documented to be glyphosate-resistant in Iowa.


Each of those weeds, Hartzler said, have pollen with the glyphosate resistance that can blow for long distances and he is anticipating a widespread problem in the near future with those pests.

“It’s time to start paying attention to weeds like we did in the 1980s,” Hartzler said.

Jim Day, agronomy manager for Pro-Cooperative based in Pocahontas, said some of the weeds that he finds producers in northwest Iowa are battling include wild buckwheat, lambsquarter, waterhemp, giant ragweed and common ragweed.

Wild buckwheat, he said, is a pest growers there have been battling for years and expects that it became more widespread during the time when many acres were dedicated to the federal conservation reserve program. It is continuing to become a bigger problem, he added.

Lambsquarter is a particular weed, Day said, that was practically eliminated at one time, but is beginning to cause more challenges in controlling it.

Day doesn’t think some of those weeds such as lambsquarter and wild buckwheat are necessarily becoming tolerant to glyphosate, but could be showing resistance to the herbicide.

“They’re not as susceptible to the herbicide,” said Day. “It’s taking more product to kill them.”

Although he has seen a significant change in how those weeds are controlled, he said they are still easily manageable.

“They are certainly manageable with the right time, right surfactant and tank mix,” said Day.

Jim Gienger, agronomy manager for Mid-Iowa Cooperative, based in Beaman, said his producers in that area are facing many of the same issues with weeds including lambsquarter, waterhemp and giant ragweed.

“Every year we are not seeing the performance we’d like,” said Gienger. “We’re just not getting the control.”

The control issues of those weeds, Gienger said, could be a simple issue of timing.

Timing, he said, is an issue. Was the field sprayed at the wrong time of day to catch the weed when it is more susceptible?

One thing that Gienger, Day and Hartzler agree on is that producers need to be doing more than just a few glyphosate applications each year and all recommend that a pre-emergent herbicide is helpful as well as tank mixes and to scout for weeds.

“Try a foundation herbicide or tank mix with something for two modes of action,” said Gienger.

“Scout, see what you got and spray accordingly,” said Day. “For the last 10 years we’ve just been using glyphosate and we are just going to build up resistance and there’s going to be trouble.”

Hartzler said scouting and learning from our neighbors in other states is helpful in controlling weeds as well.

“Implement an effective scouting program. Driving by the field isn’t an efficient way to scout,” said Hartzler.

Hartzler added that although it is too late as the weeds have gone to seed by this time, but harvest time is a great time to see what weeds survived throughout the season and to take notes to remember which plan for controlling next year.

Another tip is to get out into the field a few weeks after spraying and see what, if any, weeds are showing tolerance against the herbicides.

Contact Kriss Nelson by e-mail at jknelson@frontiernet.net.

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