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Weeds at Harvest
By Emily Unglesbee
Thursday, September 16, 2021 10:54AM CDT

ROCKVILLE, Md. (DTN) -- Those scraggly waterhemp plants or that patch of ragweed poking above your soybeans might not look like much right now, but your combine is the perfect machine to help them realize their potential.

"Combines are just really, really good weed-seed spreaders," warned Jared Goplen, an Extension crops educator at the University of Minnesota. "Weeds, and especially herbicide-resistant populations, are a lot easier to manage in small areas within a field or on a fence line as opposed to spread across a field. Anything you can do to prevent a few of those weed seeds spreading over an entire field is worth it."

Even the weed seed that stays in the hopper can be problematic, with export markets increasingly asking for grain free of "foreign material" and invasive weed seeds, Goplen noted.

So, what are your options? "None of the fun ones at this point," Goplen concedes. Pre-harvest weed management boils down to hand-pulling when possible, mowing infested fence lines, combining around big weed infestations, harvesting infested fields last and taking time to clean out equipment between fields.


If your weed infestations are small and manageable -- or you have willing labor on hand -- hand pulling them and removing them from the field is the gold standard of weed seedbank control, Goplen said.

"Even if you can't get them all the way out of the field, just laying them down between the rows will at least keep them out of the combine," he added.

But that's a tough sell with harvest looming and farmers looking at hundreds of acres to cut.

"Mowing weedy patches down is the easiest option for some of these areas," Goplen said. Mowing weed infestations that are heavily concentrated along a fence line and can be reached before harvest is a possibility at this time of year, but scattered patches within a field are trickier.

In some cases, you may need to combine around heavily infested patches in a field -- a time-consuming and sometimes demoralizing task, Goplen said. "So, try to think and plan for that before you're out there in that situation," he said. "Because there is an incredible temptation just to combine through that weed patch."

At this time of year, mowing weeds will not halt a weed infestation totally, as many plants will already have viable seeds produced and ready to germinate. It can only concentrate the weed seedbank to smaller, more manageable areas.

So, as you're mowing, map those areas for next year, Goplen added. "Make a few notes, because you will have a higher weed population in this area of the field next year," he said.

Another option is to simply combine badly infested fields or those carved-out weedy patches last and turn to the next tactic -- cleaning that combine as carefully as possible.


Try to find the time to clean the combine off before you head into another field, Goplen said.

"Some easy steps are to run the combine empty, maybe drive it across a bumpy area to rattle weed seeds out," he suggested.

But, if possible, try blowing the combine off, with special focus on the header. "That's where a lot of weed seed is concentrated," Goplen explained. "Harvest is a busy season, but anything you can do to get the dust and weed seeds off the header and feeder house is the best use of your time."

For more details on how weed seeds can contaminate your grain or create future weed problems, as well as guidance on cleaning your combine, see this University of Minnesota article, penned by Goplen and his colleagues:….

For more details on cleaning out a combine, see this Iowa State fact sheet:….

For DTN stories on the future of weed seed destructor technology in the U.S., see here:….

Emily Unglesbee can be reached at

Follow her on Twitter @Emily_Unglesbee

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