Invasive Species

What is an Invasive Plant Species?

An “invasive species” is defined as a species that is

1. Non-native (or alien) to the ecosystem under consideration; and,
2. Whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

Why are invasive plants successful?

• Many invasive plant species produce large quantities of seed.
• Many invasives thrive on disturbed soil.
• Invasive species are often first to leaf out in the spring and the last to lose their leaves in the fall, depriving native species of sunlight.
• Invasive plant seeds are often distributed by birds, wind, or unknowingly humans allowing seed to moving great distances.
• Some invasives have aggressive root systems that spread long distances from a single plant.
• These root systems often grow so densely that they smother the root systems of surrounding vegetation.
• Some plant species produce chemicals in their leaves or root systems which inhibit the growth of other plants around them.
• Invasive species have no natural enemies (insects and diseases) to keep them in check.
• Deer, rabbits and other herbivores tend to avoid invasive in favor of native plants.

Identifying and Controlling Invasive Species

Identification and eradication of invasive plants on your property should be the first step in establishing a wildlife friendly environment. Keep in mind that just because you don’t see an invasive plant spreading on your property doesn’t mean the seeds aren’t being distributed farther away. Below are resources to help you identify and control known and emerging invasive species.

• Wisconsin DNR Invasives is a good starting point. The site includes the NR40 regulated invasive species list with links identification and control information. The current list was last updated in 2015. The Wisconsin Invasive Species Council sent final recommendations for additions and changes to the list to the DNR in August 2024. See recommendations. The recommendations will now go through the formal rule making process which can take up to 31 months.
• Wisconsin First Detector Network  is a community science program that empowers people to take action on invasive species through invasive species monitoring, management, and outreach. The website has factsheets that include proper identification and proper control methods for invasives. Example
• Southeastern Wisconsin Invasive Species Consortium, Inc. (SEWISC) has information on common invasive species in our area, including some that are not on the current DNR list. They also offer invasive management workshops in the spring and fall.
• Midwest Invasive Plant Network (MIPN) has information on known and emerging invasive plants throughout the Great Lakes region. They also have an Invasive Plant Control Database which compiles and ranks the effectiveness of control methods for many invasive plants common to the Midwest.
• Woody Invasives of the Great Lakes Collaborative (WIGL) information related to woody invasive species identification, distribution, impacts, regulatory status, and control and management. The collaborative has also developed recommendations on trees, shrubs and vines that gardeners and landowners can plant as alternatives to known woody invasives.
• The Morton Arboretum- Invasive Hedge and Screen Replacement Guide Brochures with replacement recommendations for former invasive areas.

Using Pesticides to Control Invasives

Unfortunately the use of chemical controls, including the use of pesticides, herbicides, fungicides, and insecticides, is sometimes necessary to eradicate invasive species. Although chemical use can be very effective, they can be dangerous to other species or to the ecosystem in general. Before using any chemical controls research the correct application amounts and methods, and always read and follow the product instructions.

The Xerces Society’s Understanding Pesticides & Their Risks provides a summary of the risks as well as links to scientific studies on the impacts of pesticide use.

If you do use pesticides, be sure to protect yourself from accidental exposure. See Personal Protective Equipment (PPE) for Homeowner Pesticide Usage and Reduce Pesticide Exposure with Proper Gloves, Other PPE for proper precautions.