Asian copperleaf isn’t a household name in the Midwest, but in a growing cluster of Iowa fields the weed is starting to reshape farmers’ herbicide plans and harvest decisions, according to Meaghan Anderson, Iowa State University Extension field agronomist.
She reports the weed is now confirmed in 10 Iowa counties: Black Hawk (first confirmation was in 2016), Boone, Buchanan, Calhoun, Fayette, Franklin, Grundy, Hardin, Humboldt and Wright.
Farmers who have identified the weed in their fields are taking measures to control it this season, Anderson says. Others may not realize they have the weed, as it is such a newcomer in the state and no one has determined how it arrived.
Key Corridor Of Concern
Asian copperleaf is non-native to the United States. The first confirmed populations of this species were documented in New York in 1990. Currently, in Iowa, the weed’s known footprint cuts a narrow but significant swath across the center of the state.
“What’s particularly interesting to me is that Highway 20 runs through that area,” Anderson says. “There’s something about that corridor, whether it’s that the environment is well-suited for the weed or whether there’s actually something to do with the highway, we’ve really got no idea.”
The weed expanded across state boundaries this past year. University of Illinois crop scientists confirmed Asian copperleaf in Stephenson County, northwest Illinois, following corn harvest last fall. This finding is the first confirmed Asian copperleaf population in the state.
The Risk To Crop Yields
As of now, there is no concrete data from Midwest fields on yield impact from the weed in corn and soybeans yet, but Anderson does not dismiss the risk.
“There is a paper from South Korea that said with extremely high populations of Asian copperleaf, (farmers there) could see anywhere from about a 17% to 29% yield reduction in soybean,” she says.
The weed often shows up in patches along field edges, in gaps in the crop canopy, and in wetter, slow-to-grow cropping areas within fields. Those patterns make formal yield trials tricky, but growing infestations in Buchanan and Fayette counties are big enough for in-field studies this year, she notes.
“As awful and unlucky as it is for some of these farmers, it means we can now do some research in the field,” Anderson says. “Hopefully we’ll gather some more useful information, and we may be able to gather some of the yield data as well.”
Management And Control Measures
For growers currently managing the weed, Anderson says the priority is to minimize seed movement and prevent the weed’s spread. On the chemistry front for control, she stresses that the recommendations are early and based on greenhouse screening plus limited farmer experience. Even so, some trends are emerging.
“When we sprayed one of the populations with post herbicides, it was quite clear that the contact products like our Group 14s and Liberty (glufosinate) were superior to basically any of the other options we screened for post-emergence control,” she says.
She adds that growth regulator herbicides and glyphosate appear to do “OK,” but she reiterates the strongest performance has come from Group 14 contact herbicides.
“It has a really long emergence pattern, so people can, for better or worse, think of it kind of like waterhemp right now,” Anderson adds. “It’s going to emerge fairly late into the summer, as long as it’s got enough sunlight and moisture.”
New Publication Details More Insights
The biggest immediate risk for farmers in areas where the weed has been found may be simple misidentification. Crop scientists from Iowa and Illinois have put together a new flyer to provide more insignts on the new weed species: Asian copperleaf publication.
Anderson urges farmers and agronomists to push pause whenever scouting weed pressure and something looks out of the ordinary.
“This time of year, the weed will be emerging through pre-herbicides. If you’re seeing a thick mat of something that looks like waterhemp but isn’t behaving like it, let us know,” she says. “We need as many eyes on this weed as we can get.”
