Amaranthus species are among the most troublesome weed species in agronomic production systems.

Maintenance questions regarding this species have tended to focus on waterhemp. But Aaron Hager, U of I Extension weed specialist, said move over, waterhemp, Palmer amaranth is in town.

A panel of U of I specialists, including Hager, provided the most current information about crop production, pest management, and economics at the 2012 U of I Corn and Soybean Classic held on Jan. 12 at the I Hotel and Conference Center in Champaign, Ill.

Hager said Illinois farmers have become well acquainted with waterhemp and the challenges caused by this species, but Palmer amaranth is perhaps the most aggressive Amaranthus species with respect to growth rate and competitive ability.

“Palmer amaranth is most common in the southern third of Illinois but, it may be expanding its range northward,” Hager said. “The growth rate and competitive ability of this species exceed that of other Amaranthus species. Waterhemp can add close to one inch of new growth per day under good growing conditions, whereas Palmer amaranth can add multiple inches.”

Recently, at least one population of glyphosate-resistant Palmer amaranth was confirmed in southern Illinois. Hager said this should raise awareness among Illinois farmers, because this example provides additional evidence that resistance to glyphosate can occur in a summer annual weed species that is very competitive with corn and soybeans.