Asian copperleaf identified in Illinois

The genus Acalypha includes approximately 450 species that are mostly of tropical and temperate origin. Approximately five species are native to Illinois, although most are not considered weeds of Illinois agronomic cropping systems. One species previously known to grow in corn and soybean fields is hophornbeam copperleaf (Acalypha ostryifolia), but due to its later emergence characteristic it rarely results in crop yield loss. Other Illinois species in this genus that usually are found in non-crop areas include the common Virginia copperleaf (Acalypha virginica) and rhomboid mercury (Acalypha rhomboidea), and the rarer Deam’s mercury (Acalypha deamii).

In September, a retail applicator sent photographs of a plant discovered at corn harvest in a field in Stephenson County, Illinois. With the assistance of Drs. David Zaya and Geoff Levin of the Illinois Natural History Survey, the species was identified as Asian copperleaf (Acalypha australis), a species native to eastern Asia, including areas of Russia, Japan, China, and the Philippines.

Weed scientists at Iowa State University identified Asian copperleaf in an eastern Iowa corn field in 2016. Prior to that, the only other populations known to exist in the United States were in New York (first confirmed there in 1990). Since 2016, Iowa State University weed scientists have identified additional populations in eight central and western Iowa counties. Now, Illinois becomes the third state with a confirmed population of Asian copperleaf.

Little information is available that describes the biology and growth characteristics of Asian copperleaf. It exists as a summer annual species that reproduces exclusively by seed, but its emergence timing and duration are not known. Reports from Iowa State University indicate populations are frequently found at corn harvest but reports also include instances of emerged plants at the time of soybean planting.

Identification of Asian copperleaf before reproductive structures are present can be difficult. Asian copperleaf and its relatives in Illinois have leaves that alternate on the stem with serrated margins and pointed tips and bases that are very or slightly rounded. Stems are erect. Flowers in all species are not showy. Female flowers and the developing fruits have leafy tissue (bracts) that grow beneath them, and these bracts are important for distinguishing Asian copperleaf.

The best time to identify Asian copperleaf is the window of time after harvest but before frost or tilling. The Asian copperleaf plants we observed were mostly between 1 – 2 feet tall, though many were smaller. The bracts at the base of the female flowers and fruits are larger than in any other Acalypha in Illinois, with some more than ½ inch long. The bracts have very shallow teeth and are either heart-shaped or ovate (egg-shaped) with an apex that tapers to a point. Note that some sources have described bracts that are nearly round. The bracts in other Acalypha known in Illinois are smaller (typically ¼ inch long, unlikely to exceed ½ inch long) and have very long teeth that can be a quarter or half the length of the bract.

There is good potential for the development of genetic tools that can identify Asian copperleaf before maturity. However, it will take time and funding to develop and test genetic markers.

If you suspect you might have Asian copperleaf in a corn or soybean field, we can assist in verifying its identification. As mentioned, accurate identification can be difficult before reproductive structures are present on plants, but we can attempt identification of vegetative-stage plants. Kathryn Seebruck is a Commercial Ag Educator with University of Illinois Extension who covers Stephenson, Jo Daviess, and Winnebago Counties. She was able to visit the field in Stephenson County this fall along with Dr. David Zaya and is willing to assist growers should they encounter additional populations. You can contact Kathryn via email (seebruck@illinois.edu) or telephone (815-986-4357). Kathryn also produced a slide presentation on Asian copperleaf that can be viewed here: https://uofi.box.com/v/asiancopperleaf. Dr. David Zaya can be reached via email (dzaya1@illinois.edu) or telephone (217-244-1946).