Farmers and agriculture experts in corn belt states are wringing their hands over the appearance of a superweed called Palmer amaranth. The tall, tough weed is native to the southwest and has been a problem in the southern part of the country for a couple decades.

But now it’s showing up in Midwestern states like Iowa and Minnesota, and threatening to reduce corn and soybean yields.

Farmers trying to do a good thing, by planting acreage with native grasses and flowering plants, may unwittingly help to spread the weed.

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