PRAIRIE DU SAC — Canada thistle. Spotted knapweed. Crown vetch. Wild parsnip. If you’ve cruised county roads in southern Wisconsin lately, you’re sure to have seen these invasive plants growing, and maybe thriving, along the roadsides and in right of ways — areas where these plants can often easily establish themselves and spread.

Invasive plants have been shown to impact Wisconsin’s economy, environment and human health, with municipalities sometimes struggling to allocate funds and manage these plants effectively each year. It’s the reason UW-Madison Division of Extension, along with 4-Control, a Menominee-based professional vegetation control company, have partnered together to hold five roadside invasive plant workshops throughout the state this summer.

The most recent workshop was held in Prairie du Sac on July 25, using research being conducted at the old Badger Army Ammunition Plant outside of town to demonstrate how different treatment applications affect different invasive plants on Wisconsin’s roadsides.

While walking along roadsides at the old Badger Army Ammunition Plant, Mark Renz, an associate professor at UW-Madison and Extension weed specialist, paused in front of several stretches to explain different treatments and application rates he and his graduate students have been testing to combat invasive plants. With less and less money available to municipalities for spraying and mowing, it’s even more important to identify the species growing in an area and target them with the most effective treatment — whether it be broadcasting or spot treating infestations.

“All are valuable options to consider within your tool kit,” Renz said. “Weigh out your options and decide which will be your best bet.”

Best management practices, as outlined by the Wisconsin Department of Natural Resources, include scouting for, locating and documenting invasive species in an area before any activity or treatment is even applied.

Observing what is growing and identifying the density of the invasive population is important as it can dictate the scale and intensity of the treatment application, and can give municipality staff an idea of how they can use the resources available to them to manage the plants and prevent them from returning or spreading.

A full manual on best management practices for transportation and utility rights-of-way is available at The DNR also has a Forest Invasive Plant Specialist, Thomas Boos, who can be reached at 608-266-9276.

Mowing times can also be important in the fight against invasive species on roadsides. While the Wisconsin Department of Transportation has a policy in place to minimize the spread of seeds of invasive plants — southern Wisconsin should have long line shoulder mowing completed by July 1, July 15 for central counties and the end of July for counties in northern Wisconsin — it is best to mow just prior to flowering or in the early flowering stage. By mowing before seeds develop, you not only reduce the chance of spreading seeds, but in the long term, you will be saving time and money by minimizing the spread of these plants.

But as Renz cautioned, there is some variability year to year, just as there is variability in the results of treatment applications. Flowering times for invasive plants can be later in the year the farther north municipalities are within the state, along with their proximity to the Great Lakes, and the arrival of an early spring can also impact flowering times, often kick-starting them earlier.

“Pick the right treatment for the right infestation,” Renz said. “Different treatments work better for different species of invasive plants.”

There is one remaining roadside invasive plant workshop scheduled for Aug. 13 from 9 a.m. to 3 p.m. in Brown County at Way-Morr Park, 3832 Park Road, Greenleaf. The workshops have been offered at no cost thanks to sponsors Corteva Agriscience, Invasive Plant Association of Wisconsin, Nutrien Solutions, UW Extension and Wisconsin First Detector Network. However, space is limited, so please register online at

Questions about the workshops can be directed to Leo Roth at; Anne Pearce at or Mark Renz at More information on Wisconsin’s invasive plant species can be found at