Production Blog

Weeds On the Warpath

Pam Smith
By  Pam Smith , Crops Technology Editor
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Survivors next to dead weeds are a clue that you may have a herbicide-resistant weed problem. (Photo by Pamela Smith)

DECATUR, Ill. (DTN) -- Kristopher Klokkenga would like to hire a few good men or women -- anyone willing to swing a hoe. The Emden, Illinois, farmer reached out to DTN recently in hopes of finding (and hiring) the crew we featured last year to physically remove some weeds. Maybe we should start an online match site for weed warriors.

I've already spotted hoe crews at work in my travels across Illinois and Indiana. The giant ragweed looked like Christmas trees in many Indiana soybean fields last week. I'm just waiting for someone to nominate waterhemp as the state something in Illinois. Marestail could nose in as a distant second in the race for most persistent and resistant.

In a recent DTN poll, we asked how big of a problem weed resistance to herbicides has become. Only 11% of the respondents said they didn't have any problems; 18% said they had problem weed, but weren't sure the populations were resistant; 58% said weed resistance has become more problematic in recent years; 13% said they face nightmare situations.

The majority of the spraying for weeds is done for this year and now is a good time to evaluate how well your weed control programs worked and what changes might be necessary for next year. Iowa State University posted a good blog on what to look for here:…

When evaluating weed control, the first step is to properly identify the escapes. As soybeans enter reproductive stages, herbicide treatments for waterhemp are limited to a couple of Group 14 herbicides and resistance to PPO-inhibitors has been much more frequent of late.

University of Illinois weed scientist Aaron Hager wrote in a recent bulletin about the increasing incidence of multiple resistances in his state. "Waterhemp resistant to PPO-inhibiting herbicide can be controlled with glyphosate, and glyphosate-resistant waterhemp can be controlled by PPO-inhibiting herbicides. However, there are no effective herbicide options to control waterhemp resistant to both glyphosate and PPO-inhibitors in conventional or glyphosate-resistant soybean varieties. ALS-inhibiting herbicides are ineffective, and 2,4-DB will not improve control. As this stage of the season, hand removal is what is left to control multiple-resistant waterhemp," he said.

Read the rest of Hager's report and find a list of preharvest intervals for herbicides here:…

Pamela Smith can be reached at

Follow her on Twitter at @PamSmithDTN



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