There’s one more weed to put on your radar. So far, Asian copperleaf is only a concern to growers in certain Iowa counties. But it’s so new that how it got there, why it’s appearing now, and exactly how to manage it are all a mystery.

Meaghan Anderson, a field agronomist in central Iowa and Extension field specialist for Iowa State University, was among the first to receive reports and begin studying this weed. She shares what she knows in this interview with Farm Progress.

How do you describe this weed? Asian copperleaf is in the spurge family, but lacks milky sap produced by many spurges. At maturity, it has alternate leaves, 2 to 4 inches long, which are lanceolate to egg-shaped, with fine, blunt teeth and deep veins.

How tall can Asian copperleaf reach? It can grow 2 to 3 feet tall, but will be smaller under a crop canopy, where it is often first noticed. If it has sunlight, it will have many branches, but if not, there could be few branches.

Where has it been found? It has been positively identified in crop fields in eight Iowa counties: Calhoun, Humboldt, Boone, Wright, Franklin, Hardin, Grundy and Black Hawk. So far, it has not been reported in crop fields outside of Iowa.

How do you tell Asian copperleaf apart from similar weeds? Virginia copperleaf and three-seeded mercury are related species that also occur in Iowa, but these are more common in home landscapes, woodlands and disturbed natural areas. Asian copperleaf has a distinctive bract, or leaf-like structure, below the flower. It is circular to heart-shaped with teeth on the margins. Virginia copperleaf, three-seeded mercury and hophornbeam copperleaf, another agronomic weed, have deeply lobed bracts. Flowers and bracts are easily visible in the fall.

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IDENTIFYING TRAIT: The heart-shaped, leaf-like bract under the flower on Asian copperleaf identifies it. Similar species have deeply lobed bracts.

Can herbicides kill it? Herbicides can control this species when it is small, though we have no research data on what works and what doesn’t, just anecdotes and experience. It seems to be fairly well-managed with most postemergence herbicides if it is treated when plants are under 4 inches tall. We don’t yet have a good understanding about which preemergence herbicides might work. I relied heavily on information regarding what herbicides work on hophornbeam copperleaf to guide me. We hope to do research on managing Asian copperleaf in the future.

What should farmers do if they find a plant that they suspect might be Asian copperleaf after harvest? Contact your local ISU field agronomist for help in identification. If you live outside Iowa and suspect you have found it, contact your local Extension office. Report sightings yourself online. We want to learn more about this weed to help develop management strategies. It is a significant agronomic weed elsewhere in the world and is resistant to several herbicide groups.

We still do not know why it is showing up in relatively high densities in some Iowa fields.

Some information in this article can be found in “What’s the green carpet under the harvested crop?” from the ISU Integrated Crop Management newsletter, Sept. 11 edition.