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Used Combines Could Be Spreading Palmer Amaranth Seeds

You may get a whole lot more than you bargained for when you buy a used combine.

Palmer amaranth seeds lodged in a combine may travel across state or county lines with that harvester, warns Kevin Bradley, a weed scientist at the University of Missouri. “Know where your feed, seed, and equipment come from,” he says. “It is not by accident that you see Palmer amaranth growing around hay bales, feedlots, and near places where you have cleaned out your combine,” he says.

Bradley warns that Palmer amaranth is “not a weed for the faint of heart.” It is aggressively moving from the southern U.S. into the Midwest. The plant became resistant to glyphosate herbicide about four years ago. Each plant can produce as many as 300,000 seeds per plant and can grow up to 7 feet in height.

Worse yet, the summer annual can reduce soybean yields by as much as 79%.

If you have purchased a used combine from an area that might contain weed seeds like Palmer amaranth, completely clean out the harvester before heading to the field. A combine can hold almost 200 pounds of grain and material other than grain (MOG), even after the machine is allowed to “run empty” for several minutes, engineers at Purdue University discovered. Cleaning a combine can be quite the formidable task taking a minimum 45 minutes for a quick clean-out that basically consists of opening access doors followed by blowing off with compressed air, adds Dan Ess from Purdue University.

Purdue University offers a combine clean-out publication, which can be accessed by going to

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