Invasive weed threatens Midwest farm economy

University of Illinois News Bureau: An invasive weed that has put some southern cotton farmers out of business is now finding its way across the Midwest – and many corn and soybean growers don’t yet appreciate the threat, University of Illinois researchers report.

University of Illinois crop sciences professor Aaron Hager is warning Illinois farmers about Palmer amaranth, an invasive weed that can take over farm fields in a season or two. | Photo by L. Brian Stauffer

Palmer amaranth (Amaranthus palmeri), a flowering plant native to the Sonoran desert and southwest United States, has a laundry list of traits that make it a fierce competitor on the farm, said Aaron Hager, a University of Illinois crop sciences professor.

Palmer amaranth germinates throughout much of the growing season, starts earlier and grows faster than other weeds, and is a prolific seed producer, Hager said. It can tolerate drought and heat extremes that would kill other plants. And it is becoming resistant to the most common herbicides used to combat it, he said. Killing the plant before it can go to seed is the best way to control it, he said. That means treating young plants with herbicides when they are less than 4 inches tall. “Once it is taller than 4 inches, the effectiveness of herbicide treatments drops off very dramatically and very quickly,” Hager said.

Catching the plant that early is problematic, however. As a seedling, Palmer looks a lot like waterhemp, another problematic weed that is difficult to control. This means farmers have the dual challenge of determining whether Palmer has invaded their fields and, if it has, taking effective action to kill it before it takes over...

Photo by Aaron Hager. Palmer amaranth grows very fast, germinates throughout the season, produces lots of seeds, can tolerate heat extremes and is very adaptable, researchers report