While growers wonder if Palmer amaranth populations will be able to adapt to the growing conditions of Illinois, results from a recent University of Illinois study suggest that it is a question of when and where, not “if” pigweed will become established in the state.

“Perhaps a more important question now concerns the damage niche of Palmer amaranth populations in Illinois agronomic cropping systems,” said Aaron Hager, a U of I associate professor of weed sciences.

Palmer amaranth (Amaranthus palmeri) has garnered much attention recently in both academic discussions and popular press releases, and with good reason, Hager said. Among the weedy species of Amaranthus, Palmer amaranth has the fastest growth rate and is the most competitive with the crops common to Midwest agronomic cropping systems. 

According to Hager, soybean yield losses approaching 80 percent and corn yield losses exceeding 90 percent have been reported in peer-reviewed scientific literature. 

“Palmer amaranth can be effectively managed in Illinois agronomic crops, but the greatest likelihood for successful management is with systems that employ multiple effective management tactics,” he said. “Palmer amaranth is perhaps the personification of a weed species that requires an integrated management approach.”

Unlike waterhemp, Palmer amaranth is not indigenous to Illinois. The pigweed evolved as a desert-dwelling species in the southwestern United States, including areas of the Sonoran Desert. However, genotypic and phenotypic adaptability have allowed Palmer amaranth to expand its distribution and colonize across much of the eastern half of the United States.

“It is likely that Palmer amaranth was introduced by seeds moved into Illinois from areas where Palmer amaranth has become the dominant pigweed species,” Hager said.