What's that Green Carpet Under the Harvested Crop?

As corn and soybean are taken out of fields, some fields may reveal an unexpected mat of Asian copperleaf lurking below the canopy. As of this summer, we’ve identified Asian copperleaf (Acalypha australis) in crop fields in eight counties: Calhoun, Humboldt, Boone, Wright, Franklin, Hardin, Grundy, and Black Hawk. Early identification of this species is key to adopting effective management tactics to reduce its spread to other fields.

Asian copperleaf is in the spurge family but lacks the milky sap produced by many spurges. At maturity, the plant has alternate leaves that are 2-4 inches long, lanceolate to egg-shaped, with fine, blunt teeth and deep veins (Figure 1). Plants can reach heights of 2-3 ft., though may be smaller if under a crop canopy. Plants that receive more sunlight are highly branched, while those under the canopy have few branches (Figure 2).

This species is often found under the crop canopy at harvest time (Figure 3). As fall approaches, the upper leaves on plants may develop a reddish or coppery color (Figure 4). Unlike waterhemp, Asian copperleaf does not have long flowerheads/inflorescences at the tops of stems, instead producing flowers and seed primarily along stems.

Virginia copperleaf and three-seeded mercury are two other Acalypha species present in Iowa with a similar growth habit. These two species are more common in home landscapes, woodlands, and disturbed natural areas; it is unusual to find them in crop fields. The distinguishing characteristic of Asian copperleaf from the other Acalypha species are the bracts located beneath the flowers. The bracts of Asian copperleaf are circular to heart-shaped with a toothed margin (Figure 5). Both Virginia copperleaf and three-seeded Mercury have deeply-lobed bracts (Figure 6). It is difficult to confidently differentiate these species prior to flowering and development of the bracts, but all Acalypha species should be flowering this time of year and thus have easily identifiable bracts.

While the magnitude of the threat posed by this weed in Iowa remains unknown, it is a significant agronomic weed in other areas of the world, has evolved resistance to several herbicide groups, and has been found at high densities in several Iowa fields in recent years. Due to the ease of identification this time of year, please keep an eye out for this species during harvest. If you find a plant you suspect might be Asian copperleaf, please contact your local Iowa State University Extension and Outreach field agronomist for assistance with identification. You can report sightings yourself at https://go.iastate.edu/FGA4NK.