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July 1, 2025

July Weed of the Month: Harmful Impacts of Invasive Plants

Many of the invasive plants listed on Minnesota’s Noxious Weed List threaten ecosystems, agriculture, and public health

By Emilie Justen, Minnesota Department of Agriculture - Minnesota is known for its diverse landscapes and ecosystems. Residents and tourists enjoy the state’s abundant natural resources by visiting public parks, exploring our vast network of recreational trails, fishing on our pristine lakes, and other outdoor activities. From forests to prairies, rivers, and lakes, the state hosts thousands of native plants and animals adapted to varied ecosystems.

However, invasive plants can put a damper on our enjoyment of the outdoors. Many of the invasive plants listed on Minnesota’s Noxious Weed List can be harmful or toxic to humans, animals, and even entire ecosystems. For example, sap from wild parsnip, an invasive plant commonly found on roadsides and grasslands, causes burns and blisters to skin. Wild parsnip is related to wild carrot, also known as Queen Anne’s lace, which can also cause uncomfortable skin irritation.

Wild parsnip is commonly found along roadsides and in fields.

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Other species on the noxious weed list may cause skin irritations as well. Common and cutleaf teasels, hooked hair hops, and Canada and plumeless thistles all have sharp prickles on the stems and leaves that can cause painful scratches and inflammation.

Invasive shrubs such as buckthorn and Japanese barberry can also contribute to human health impacts. Invasive shrubs create favorable humidity conditions for black legged ticks to thrive. Black legged ticks are carriers for several pathogens that cause diseases in humans, livestock, and wildlife, including Lyme’s, anaplasmosis, and babesiosis.

Several noxious weeds can be toxic if ingested. Grecian foxglove toxicity can cause abnormal heart rhythms and can be toxic to livestock if dried and baled. Poison hemlock is toxic if ingested or if it's sap is absorbed through skin. Common tansy toxicity can cause liver and brain damage.

Invasive plants don’t just affect humans and livestock. Two species on the noxious weed list are also toxic to monarch butterflies. Black and pale swallow-wort are two vining milkweeds that are found in very small populations in Minnesota. Though they are related to our native milkweeds, they are toxic to monarch caterpillars, and eggs that are laid on their leaves will not survive.

In addition to direct health impacts, invasive plant species on the noxious weed list disrupt native ecosystems by displacing native plants and degrading critical habitats. Garlic mustard, invasive woody shrubs, and purple loosestrife are all established invasive species that have direct negative impacts to Minnesota’s natural resources. Garlic mustard suppresses native woodland wildflowers. Invasive woody shrubs prevent native tree seedlings from growing and replacing forest canopy. Purple loosestrife changes shoreline habitat and can change water chemistry of lakes and wetlands.

Several resources are available to help you learn about invasive plants and livestock toxicity. You can learn more about the noxious weed list at the Minnesota Department of Agriculture’s Noxious Weed List webpage. The webpage has information on each of the species listed. Each page has photos of the species with identifying characteristics and the impacts on humans, livestock, and the environment. Additionally, if you need help identifying a species, you can create a report through our Report A Pest form. For information about livestock toxicity, the University of Minnesota maintains a webpage of Plants Poisonous to Livestock.

You can help preserve Minnesota’s rich ecological diversity by being a good land steward. When you learn about invasive plants and the harm they can cause, you’ll be better prepared to prevent their introductions and develop management plans for your own property. This will help preserve the diverse landscapes and ecosystems for generations to come!

For more information on noxious weeds and invasive insects, listen and subscribe to Smarty Plants, a Minnesota Department of Agriculture podcast. 

MEDIA: Contact Brittany Raveill, MDA Communications, at [email protected] or 651-201-6131 for more information on Weed of the Month