New Invasive Weed Threatens Corn and Soybean Fields Across Minnesota
A newly detected weed species is raising concerns among Minnesota farmers and weed specialists. Asian copperleaf (Acalypha australis) was identified in a Rice County corn field in fall 2025, prompting calls for increased field monitoring and early management.
Native to eastern Asia, the invasive weed has spread to several areas of the United States. Its presence in Minnesota raises questions about its potential to spread through corn and soybean fields and create additional weed management challenges.
Sithin Mathew, Weed Science Graduate Student, Matt Pfarr, Former Crops Extension Educator, and Debalin Sarangi, Extension Weed Scientist, from the University of Minnesota provided information about the plant's identification, spread and potential risks to crop production.
Background and Spread of Asian Copperleaf
Asian copperleaf originates from eastern Asian countries, including China, Japan, Korea, the Philippines and parts of Russia. It grows in grasslands, cultivated fields, slopes, and areas where soil has been disturbed.
The first recorded detection in the United States occurred in New York in 1990. The weed was later discovered in an Iowa corn field near Cedar Falls in 2016. It has since been reported in at least eight Iowa counties and in Illinois.
The Minnesota discovery raises concerns about further movement throughout the Midwest. Farmers should pay particular attention during harvest, when removing crop cover can reveal weeds that were previously difficult to see.
Why Farmers Should Scout in Fall
Asian copperleaf is an annual broadleaf weed that reproduces through seeds. Germination generally begins in late April or early May, although seedlings may continue emerging throughout the summer.
Young plants can resemble other weed species, making identification challenging. Mature plants are often easier to recognize because their leaves and reproductive structures become more noticeable.
In open sunlight, plants can grow 2 to 3 feet tall. Those growing beneath corn or soybean canopies typically remain shorter, sometimes reaching only about 18 inches. Upper leaves may develop reddish or copper-colored tones in late summer and fall.
Recognizing Asian Copperleaf in Fields
Farmers can look for several characteristics when identifying the weed.
- Leaves: Leaves measure approximately 2 to 4 inches long, with lance-shaped to egg-shaped forms, small-blunt teeth along the edges and wrinkled surfaces caused by raised veins.
- Growth habit: Plants grow upright and may become taller in areas receiving full sunlight.
- Color: Upper leaves may turn reddish or copper-colored toward the end of the growing season.
- Flowers: Unlike waterhemp, which produces elongated flower spikes, Asian copperleaf produces flowers along its stems.
- Bracts: Toothed, heart-shaped to nearly round structures appear beneath individual flowers. Native copperleaf species generally have more deeply divided bracts.
Farmers should examine multiple plant characteristics before making an identification, as leaf color alone is not enough to confirm the species.
Seed Production and Herbicide Resistance Risks
Asian copperleaf spreads through seeds, with each plant capable of producing hundreds. The seeds may remain viable in soil for several years, although their exact survival period under Midwestern conditions has not been established.
Seeds can move between fields through contaminated machinery, soil and crop residue. Plants that escape detection along field edges or beneath crop canopies may produce seeds before farmers recognize an infestation. Regular scouting and equipment cleaning can help reduce this risk.
The USDA identifies Asian copperleaf as a high-risk invasive weed. Researchers are also concerned about herbicide resistance. Resistant populations have been reported in Asia for glyphosate (Group 9), ALS inhibitors (Group 2) and PPO inhibitors (Group 14).
These herbicide groups are commonly used in Midwestern crop production, potentially making future control more difficult. Research in Asia has also documented yield reductions of up to 50% in heavily infested crops, including cotton, pulses, and vegetables. However, the potential yield impact on Minnesota corn and soybeans remains unknown.
Steps Farmers Can Take
Farmers should inspect corn and soybean fields during harvest, focusing on field borders, shaded locations and areas containing unfamiliar weeds. Cleaning equipment and avoiding the movement of potentially contaminated soil and plant material can help prevent seeds from spreading.
Anyone who suspects Asian copperleaf in a field should contact Extension Weed Scientist Dr. Debalin Sarangi at dsarangi@umn.edu or reach out to a local Extension office. Experts can confirm the plant's identity and recommend appropriate management practices.
Photo Caption: Asian copperleaf growing in a corn field in Rice County, MN
Photo Credit: Debalin Sarangi, UMN Extension