-Farm News photos by Darcy Dougherty Maulsby
Gentry Sorenson, an Iowa State University Extension field agronomist, shared information about Asian copperleaf weeds during a recent field day in northern Iowa.

In the ongoing battle against weeds, a newcomer called Asian copperleaf is raising concern across Iowa.

In the last few years, Asian copperleaf has usually been detected in fields during harvest in Iowa.

“Farmers have alerted us to Asian copperleaf presence at harvest, where it formed thick mats under the canopy in corn and soybeans,” said Meaghan Anderson, an Iowa State University Extension field agronomist in central Iowa.

Asian copperleaf has been found in a number of Iowa counties including Boone, Calhoun, Franklin, Humboldt, Grundy and Black Hawk. This weed is a big mystery in many respects.

“We used to think this weed germinated in June, but my colleague found Asian copperleaf in central Iowa by the second week of May this year,” said Angie Rieck-Hinz, an ISU Extension field agronomist in north-central Iowa. “I found it in Franklin County in north-central Iowa by the third week of May 2024.”

-Farm News photo by Darcy Dougherty Maulsby
Attendees at an ISU Extension field day near Kanawha got an up-close look at Asian copperleaf this summer.

Asian copperleaf (Acalypha australis) was first discovered in Iowa in 2016 in a corn field near Cedar Falls, reports ISU Extension. Prior to this discovery, the only documented infestation in North America was within New York City. “No one has found it in Illinois, Missouri, Minnesota, Wisconsin or states other than Iowa and New York,” Rieck-Hinz said. “We still don’t know a lot about this weed.”

It’s unclear how the plant was introduced to Iowa, Anderson added.

“These discoveries are the only known cases of Asian copperleaf infesting cropland in the United States,” she said

Since the initial discovery in Iowa, Asian copperleaf has been found in multiple locations across central and northern Iowa. In each field, ISU agronomists report that several dense patches of the weed were present throughout the fields, suggesting it was in the field for several years before being identified.

“There’s a farm in Wright County that’s had trouble with Asian copperleaf for about five years,” said Rieck-Hinz, who spoke in June at the Northern Research and Demonstration Farm’s field day near Kanawha. “They didn’t know it was Asian copperleaf. They just knew they couldn’t kill it.”

Beware of herbicide resistance

The magnitude of the threat that Asian copperleaf poses to Iowa row crops is unknown.

“We don’t know if it’s as prolific as waterhemp,” Rieck-Hinz said.

Several things are clear, however. Asian copperleaf is a significant agronomic weed in other areas of the world, Anderson said. It has evolved resistance to several herbicide groups, and it has been found at high densities in multiple Iowa fields in recent years. Populations of Asian copperleaf have shown resistance to various groups of herbicides, including HG 2 (ALS inhibiting), HG 9 (glyphosate), and HG 14 (PPO inhibiting) herbicides.

During the field day at Kanawha, one farmer asked whether cover crops can smother Asian copperleaf weeds.

“We don’t know for sure, but cover crops are definitely a useful tool in the toolbox,” said Gentry Sorenson, a field agronomist in northwest Iowa for ISU Extension and Outreach.

So the question remains — how do you kill Asian copperleaf? “We don’t know,” Rieck-Hinz said.

Keep an eye out for Asian copperleaf

Asian copperleaf is in the spurge family, but lacks milky sap common in many spurges.

The weed’s leaves are 2 to 3 inches long, with serrated (finely-toothed) edges. The distinguishing characteristic of Asian copperleaf weeds are the bracts located beneath the flowers. The bracts are circular to heart-shaped.

“Asian copperleaf really likes light,” Rieck-Hinz added. “If it’s in full sun, it can easily reach heights of 2 to 3 feet, although it will be shorter under canopy.”

As the weed continues to spread, there’s evidence that Asian copperleaf is moving with water — in some cases for almost half a mile, Rieck-Hinz added.

When crop scouting this summer, keep an eye out for Asian copperleaf. The species remains under the crop canopy throughout the growing season, according to ISU Extension agronomists.

Identifying Asian copperleaf can be tricky. Not only are there other copperleaf plants in Iowa (including Virginia copperleaf), but Asian copperleaf can look similar to other weeds. “If you’re just walking along, Asian copperleaf can look like waterhemp,” Rieck-Hinz said.

ISU Extension and the Iowa Department of Agriculture and Land Stewardship are asking farmers and others in the ag industry to keep an eye out for this plant as fields are harvested this fall. If you find a plant you suspect might be Asian copperleaf, contact your local ISU Extension field agronomist for assistance with identification.

ISU Extension agronomists will continue to monitor Asian copperleaf populations this summer to gain a better understanding of their emergence patterns and the effectiveness of post-emergence herbicides on this species.

“We also plan to collect enough Asian copperleaf seed this fall to conduct greenhouse trials to learn more about this weed,” Rieck-Hinz said.