Corn and soybean farmers should be scouting for a new weed this upcoming growing season. According to University of Illinois crop experts, Asian copperleaf (Acalypha australis) was identified in a field in Stephenson County in northern Illinois following corn harvest last fall. This finding is the first confirmed Asian copperleaf population in Illinois.
“It is more advantageous to remain in front of a new weed challenge rather than allow it to get in front of researchers and producers,” says Aaron Hager, weed science professor and University of Illinois Extension faculty specialist in the Department of Crop Sciences, part of the College of Agricultural, Consumer and Environmental Sciences.
Asian copperleaf is non-native to the United States. The first confirmed populations of this species were documented in New York in 1990. The next time Asian copperleaf was positively identified in the U.S. was in an Iowa seed corn field in 2016. Since then, it has been confirmed in 10 counties across central and western Iowa. Illinois is the third state with a confirmed population of Asian copperleaf.
Reports of herbicide resistance in Asian copperleaf populations in its native range raise concerns that it could evolve herbicide resistance in U.S. populations as well. In addition to its rapid spread and persistence, an uncontrolled population could quickly become problematic.
“Our goal is to give Illinois farmers and weed management practitioners the information necessary for them to scout and identify populations of Asian copperleaf,” says Hager. “We hope this will allow any additional populations to be identified so that management can be implemented to reduce the movement of seed to additional fields.”
Asian copperleaf is a summer-annual species that reproduces exclusively by seed, but its emergence timing and duration are not known. Weed scientists at Iowa State University have received reports indicating that populations are frequently found at corn harvest, but there have also been reports of emerged seedlings at soybean planting.
Identifying Asian copperleaf before reproductive structures are present can be difficult. Its leaves are alternately arranged on the stem and have serrated margins, pointed tips, and slightly to very rounded bases. Stems are erect, and flowers are not showy. Leafy tissues, called bracts, grow beneath the female flowers. These bracts are important for distinguishing Asian copperleaf from native Acalypha species such as Virginia copperleaf (Acalypha virginica), rhomboid mercury (Acalypha rhomboidea), and the rarer Deam’s mercury (Acalypha deamii).
“Asian copperleaf’s relatives are native to Illinois, growing in grassy areas, woods, and sometimes as yard weeds,” says David Zaya, associate research scientist and botanist with the Illinois Natural History Survey at U. of I. “The best way to tell Asian copperleaf apart is the leafy tissue under the flowers.”
According to Zaya, if it looks like a small hand or lopsided star with long “fingers,” it is one of the native species. If it looks like a heart or egg with a pointed tip, it is probably Asian copperleaf. The other clue would be if there are hundreds of thousands of them in an agricultural field, then it is probably Asian copperleaf.
Asian copperleaf is most easily identified after harvest. The Asian copperleaf plants observed in Stephenson County ranged from 1 to 2 feet tall, though many were smaller. The bracts at the base of the female flowers and fruits are larger than in any other Acalypha species in Illinois, with some more than one-half inch long. The bracts in other Acalypha species known in Illinois are smaller at typically one-quarter inch long, and unlikely to exceed one-half inch long. The bracts in Asian copperleaf have a much different shape.
Farmers are encouraged to keep an eye out for this species while scouting during the upcoming growing season. While initial reports of this weed in Iowa were made during harvest, it is advised to scout for it prior to planting and throughout the growing season. Preventing the spread of seed is crucial to limiting future infestations. Fields containing Asian copperleaf should be harvested last, and combines should be cleaned before moving fields to prevent seed movement.
To learn more about identifying and managing Asian copperleaf, view and download Extension’s Asian Copperleaf fact sheet at go.illinois.edu/AsianCopperleaf.
If growers suspect Asian copperleaf in a corn or soybean field, Illinois Extension staff can assist in verifying its identification. Contact Kathryn Seebruck, commercial agriculture educator at seebruck@illinois.edu or 815-986-4357.