Asian copperleaf (Acalypha australis) remains a new species of concern in Iowa. Currently, we’re aware of infestations in eight Iowa counties: Calhoun, Humboldt, Wright, Boone, Franklin, Hardin, Grundy, and Black Hawk (Figure 1). This species is often first detected at harvest, where farmers discover a carpet of green plants under corn and soybean canopies. Now is a great time to look for this species and other new weeds (like Palmer amaranth) when scouting fields.
This summer, several clients have reached out with images of other copperleaf species (Figure 2). While other copperleaf species can be problematic in crop fields, they have not historically been an issue in Iowa crop fields. Many copperleaf species have similar vegetative characteristics: one first set of opposite leaves followed by alternate leaves, ovate leaf shape with blunt teeth on leaf margins, and significant branching. Floral characteristics are necessary to differentiate between species like Virginia copperleaf, rhomboid copperleaf, and Asian copperleaf.
One simple trait to look for is the shape of the bracts, modified leaves associated with flowers, on mature plants. Copperleaf bracts form something like a cup that nests directly underneath flowers and different species have different shaped bracts. Asian copperleaf has distinct heart-shaped bracts located below the flowers with blunt teeth around the margins, while other copperleaf species have bracts with distinct lobes (Figure 3).
Twice in the last week, we’ve identified rhomboid copperleaf (Acalypha rhomboidea) in scattered populations in crop fields; one of these was in Linn County and one was in Boone County. Unlike Asian copperleaf, rhomboid copperleaf is native to the Cornbelt. While I have not seen Asian copperleaf flower yet this growing season, the rhomboid copperleaf found in two Iowa fields is flowering. Upon close inspection, it was easy to tell the bracts were not correct for Asian copperleaf (Figure 4).
Please continue to keep an eye out for copperleaf plants in crop fields. If you find a population that you suspect is Asian copperleaf, your local Iowa State University Extension and Outreach field agronomist can help confirm it.
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- Field Agronomist in Central Iowa