MINNEAPOLIS — An aggressive southern weed called Palmer amaranth apparently has turned up in Minnesota for the first time, University of Minnesota Extension experts said Wednesday.

Palmer amaranth has been spreading northward in recent years from the south, where it’s been a frustrating scourge for farmers. The weed can shoot up as high as 7 feet, and just one plant can produce 500,000 to 1 million tiny seeds. Herbicide is increasingly futile against it, and the weed’s thick stems and deep roots make it hard to kill by hand. It has already turned up in Iowa, Wisconsin and South Dakota.

Integrated pest management specialist Bruce Potter said he saw it Tuesday after a crop consultant spotted suspected Palmer amaranth in a field in Yellow Medicine County in western Minnesota and gave him a call.

Extension agronomist Jeff Gunsolus said he was waiting to receive a plant sample Friday before officially confirming the finding, but he said he’s confident it’s Palmer amaranth. He said he decided to put out the information now so that farmers can check their fields before they get busy with the fall harvest.

“I know what it looks like. I’ve been in Tennessee. I’ve been in Arkansas. I’ve seen the plant. This is pretty definitive,” Gunsolus said.