A single plant that showed up this summer on the edge of a southwestern Ontario cornfield is cause for concern among Canadian farmers.

Ontario provincial weed management specialist Mike Cowbrough says the plant in question, found in Wellington County, is confirmed as palmer amaranth.

The species has previously been dubbed the most troublesome weed in U.S. agriculture, but hasn’t yet appeared in Canada in a significant way; its only other recent known appearance in Canada outside Ontario was by a couple of plants in a southern Manitoba bean field in 2021.

While the broadleaf weed is known for its physical height — up to eight feet — and aggressive rate of spread, it’s also infamous in the U.S. and elsewhere for its adaptability against herbicides, making it even more difficult to keep in check.