Keep an Eye out for Asian Copperleaf

By Meaghan Anderson

With yet another sighting of Asian copperleaf (Acalypha australis) this fall, it’s a good reminder to keep an eye out for this new species during harvest. Asian copperleaf (Acalypha australis) was first discovered in Iowa in 2016 in a corn field near Cedar Falls. Prior to this discovery, the only documented infestation in North America was within New York City. Since the initial discovery, it has been found in four other locations, totaling five counties across north central Iowa (Figure 1). In each field, several dense patches of the weed were present throughout the field (Figure 2), suggesting it was in the field for several years before being identified.

It is still unknown how the plant was introduced to Iowa. These discoveries are the only known cases of Asian copperleaf infesting cropland in the United States. The plant is a threat to row crops in its native range. Sources note this species has populations resistant to HG 2 (ALS inhibiting), HG 9 (glyphosate), and HG 14 (PPO inhibiting) herbicides in its native range. A USDA Risk Analysis completed in 2012 stated that the species did not show ‘any strong invasive or weediness characters’, but because of a high level of uncertainty the plant was classified as “High Risk” in 57% of the simulations.

Identification

Asian copperleaf is in the spurge family but lacks milky sap common in many spurges. It is an erect plant that can reach heights of 2-3 ft., but most plants found in Iowa were less than 18” in height. Leaves are 2-3” long, lanceolate with serrated (finely toothed) edges. The distinguishing characteristic of Asian copperleaf are the bracts located beneath the flowers. The bracts are circular to heart-shaped with a dentate margin (Figure 3). Virginia copperleaf and rhombic copperleaf, two other Acalypha species present in Iowa with a similar growth habit, have deeply lobed bracts (Figure 4). It is unlikely that anyone could confidently differentiate between these species prior to flowering. Asian copperleaf seems to emerge later in the season than other weed species; we found cotyledon-stage seedlings at one location on June 14. The species remains under the crop canopy throughout the growing season.

Figure 3. Asian copperleaf has circular to heart-shaped bracts beneath flowers. (Photos courtesy of Bob Hartzler and Robin Pruisner)

Figure 4. Deeply lobed bract like that from Virginia copperleaf and rhombic copperleaf (left) compared to a heart-shaped bract from Asian copperleaf (right). Photos courtesy of Bob Hartzler.  

Requested action. The Iowa Department of Agriculture and Land Stewardship and Iowa State University have continued interest in determining how widespread the weed is across the state. By determining how much area is infested with this weed, we can better estimate the risk it poses to Iowa crop production. In all cases, the Asian copperleaf was detected in fields during crop harvest. Thus, we are requesting that farmers and others in the agricultural industry keep an eye for this plant as fields are harvested.