Unwanted hitch-hikers may grab a ride to the Midwest on used farm equipment, hay, straw and feed from the south, says University of Missouri weed scientist Kevin Bradley.
The offending travelers? Palmer amaranth seeds, he says.
"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."
Bradley considers Palmer amaranth the No. 1 weed to watch – "not for the faint of heart," he says.
The weed is aggressively moving from the southern United States into the Midwest and north-central U.S.
Bradley says it is resistant to glyphosate herbicide, and each plant can produce up to 300,000 seeds. They can reach 7 feet in height.
In the coffee shop, it is known as Palmer pigweed. In university circles, it is referred to as Palmer amaranth. Whatever you want to call it, this weed is the No. 1 weed to watch. Stay on top of your control plan with our new free report, Palmer Amaranth: Understanding the Profit Siphon in your Field.
The effects don't stop there. Palmer amaranth's root system takes nutrients and water from crops and can reduce soybean yields by as much as 79%, MU says.
Identifying Palmer amaranth is difficult in early stages of growth, but Palmer amaranth's seedling cotyledons are narrow and green to reddish in color. Mature Palmer amaranth plant petioles are usually longer than the leaves. The leaves have a poinsettia-like arrangement when viewed from above.
While it's easier to identify by its seed head at the end of the growing season, by then it's too late.
MU suggests controlling Palmer amaranth by integrating narrow row spacing, cover crops and tillage where appropriate in combination with multiple herbicide modes of action, especially in the form of pre-emergence herbicides.
"This cow's out of the barn and I don't know that we can ever close it," Bradley says. "But we should try."