Asian copperleaf found in another Iowa county

Asian copperleaf was recently confirmed in Franklin County, Iowa, making it the fifth north-central Iowa county to grapple with the weed. Asian copperleaf was first discovered in Iowa in 2016 in a cornfield near Cedar Falls.

Asian copperleaf (Acalypha australis) is an annual weed species that is native to eastern Asia and has been found in Australia and parts of Europe. It’s not clear how it came to be in Iowa crop fields and does not appear to be particularly invasive, but the plant is a threat to row crops in its native range. Two sources note this species has populations resistant to herbicide group 9 (glyphosate) and group 14 (PPO inhibiting) in its native range.

Meghan Anderson, an Iowa State Extension field agronomist, says, “It appears to emerge very late. I don’t think it’s surviving a herbicide application. I think herbicides are controlling it well. It’s emerging late enough that it’s coming up after the herbicides have petered out during the growing season.”

Asian copperleaf is shade tolerant and remains under the crop canopy throughout the growing season. Anderson says that it’s not a surprise that it appears to be shade tolerant. “There’s other copperleaf species that are known to also be shade tolerant. One that is a problem in southern row crops is hophornbeam copperleaf, and there are a couple of other copperleaf species found in Iowa that are also typically found in areas receiving partial shade.”

How to identify Asian copperleaf

Asian copperleaf is in the spurge family but lacks milky sap common in many spurges. It has a similar leaf shape and plant size to the other copperleaf species found in Iowa and the Midwest. Leaves are 2 to 3 inches long, lanceolate with serrated (finely toothed) edges. It would be very difficult to distinguish Asian copperleaf from native copperleaf species prior to flowering. 

“For the copperleaf species, the big distinguishing feature is those bracts,” Anderson said. “Bracts are modified leaves that surround the floral structures. Virginia copperleaf has bracts that almost look like a hand gripping around the bottom of the flower. Whereas, Asian copperleaf has more of a heart-shaped cup that will surround the bottom of the flower.”

Anderson also notes that Virginia copperleaf is not normally found growing in agricultural fields. Prickly sida is another species that has a similar appearance that may be found in fields this time of year, particularly in southern Iowa. “Prickly sida could be confused with Asian copperleaf, but those bracts surrounding the flowers will make it easy to differentiate it,” she said.

Because this is an annual species, dispersal is by seed. Seeds are small (larger than waterhemp but smaller than foxtail). “It’s likely that they would move across the landscape within a field by water,” according to Anderson. As for longer-distance spread, she says, “Human assisted movement is my biggest suspicion right now through moving soil that is potentially contaminated with it.”

Potential yield impacts of Asian copperleaf

Because it germinates later in the season, yield impacts from this species are currently expected to be minimal. However, it can create a dense mat. “I would expect it to be quite effective at shading out any species that may try to germinate in the late summer or early fall like cover crops or winter annual weeds. However, it does seem to freeze out rather quickly so it may not inhibit growth of cover crops in the long term.”

Keeping an eye out for Asian copperleaf

So what should you do if you suspect that you have Asian copperleaf in your field?

The Iowa Department of Agriculture and Iowa State Extension want to keep tabs on where Asian copperleaf is showing up to better understand the risk it poses to Iowa crop production.

“We appreciate everyone keeping an eye out for it and this is the best time of year to notice this weed. If anyone harvests their field and finds a carpet of a weed they don’t recognize under their crop, we would very much appreciate a phone call to help them identify it to find out if it is Asian copperleaf.” says Anderson.

Anderson welcomes farmers to reach out to her. “Good pictures are really helpful for identification. We would also be asking for field history information: How long have they been dealing with Asian copperleaf, rotation history, any manure applications, custom work, tiling that might be considered unusual just in an effort to track down where this might be coming from.”