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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Giant reed grass. © S. Kelly Kearns
Beware the invaders: Giant reed grass is filling in shoreline areas in Green Bay and other northeastern waters.

© S. Kelly Kearns

June 2001

Weeding wild places

Communities and land managers are coming together to take invasive weed control into their own hands

S. Kelly Kearns

Sources for further information | Twenty-four to watch for (chart)

It is a beautiful late spring day as we hike through a friend's woodland, my children asking the names of the wildflowers they spot along the way. Suddenly they cry out and start pulling bright green leafy plants out of the ground. Before I can even call to them to stop, I smell the problem! The strong garlic-like odor verifies that my young botanists have spotted another patch of garlic mustard. We are fortunate that this patch and several like it in this woods are still small – small enough to pull all the plants by hand.

My son unpacks the plastic bag we brought just in case we spotted this European invader. He warns his sister and me not to leave any of the flowering plants on the ground, or they may produce seed. As we pull the hundreds of plants, we notice that in this patch the invaders have already excluded the otherwise abundant wildflowers. I remind the kids that since garlic mustard is an edible plant, they could safely eat the leaves and flowers, but when they pull most invasive plants they should be wearing gloves. Before we leave the area we mark the site with a bright orange ribbon and take note of the location so our friend can return for the next several years to pull the plants that will emerge from seeds already waiting in the soil.

Garlic mustard is one of our relatively recent weeds, spreading rapidly in woodlands throughout much of southern and eastern Wisconsin in the last 15-20 years. Other weeds, such as buckthorn and honeysuckle shrubs, have been around for several decades, spreading their seeds with the aid of birds from one woodland to the next. Wind and water help disperse many weed seeds, while mowing equipment, tires and boots are often unintentional vectors that expand the range of many invasive plants. As these plants spread, they often shade out and displace native wildflowers, ferns and tree seedlings, altering wildlife habitat and leaving only bare soil or a single species carpet of weeds on the forest floor.

Some of these plants, such as multiflora rose and autumn olive, were intentionally planted – grown by agencies such as the Department of Natural Resources and Soil Conservation Service. Landowners were encouraged to plant them as windbreaks and for wildlife habitat. Although Wisconsin DNR discontinued the sale of all invasive non-native trees and shrubs 20 years ago, the plants still remain on the landscape, spreading their progeny further each year. It is only in retrospect that we realize the folly in suggesting that rapidly growing plants from another part of the world would be better for our native wildlife than the native plants they evolved with.

The good news is that many forests, particularly those in the Northwoods, have not yet been impaired or overrun by garlic mustard and other aggressive plants. Due to our cold, long winters and our location near the center of the continent, many species that infest regions to our south, east and west have not yet spread to Wisconsin. However, we know that many of these species are expanding their range. Of particular concern are species that might take advantage of the warmer winters and longer growing seasons that we have experienced in recent years. Japanese honeysuckle and kudzu – two vines that blanket millions of acres in the southern U.S. – have moved as far north as central and northern Illinois.

Garlic mustard. © Robert Queen
Pungent and prolific, garlic mustard has gained a foothold only in the past 15-20 years.

© Robert Queen.

We still have some time to teach landowners and others about plants they need to vigilantly watch for and remove before allowing an infestation to expand. In recent years awareness of the issue has blossomed. Landowners and public land managers are clamoring for information on ways to identify and control plants that are invading their woodlands, grasslands, wetlands and lakes.

In response to this interest, many individuals and organizations have taken on the task of educating the public and local administrators about ways to control invasive plants locally. A few examples:

  • The Milwaukee County Park People have galvanized thousands of volunteers to pull garlic mustard and cut buckthorn from Milwaukee County parks.

  • A group in Sauk County is working with highway maintenance crews to encourage them to mow and spray in ways that better contain roadside weeds and slow their spread into adjacent farm fields, grasslands and forests.

  • Land managers on public lands and private conservation areas are regularly experimenting with control methods to see what practices work best in their regions. They are sharing their results with others.

  • The Great Lakes Indian Fish and Wildlife Commission has developed an online pilot project to show the range of purple loosestrife and keep records of new occurrences.

  • Hundreds of cooperators are rearing beetles to feed on loosestrife populations in their communities.

  • A technical advisory committee has worked for the last two years developing a proposal to help the state legislature revise state weed laws to be more effective while not making unreasonable demands of landowners.

Although concern about the spread of invasive species is growing, there is still much to be done. We need to find ways to screen new species before they are introduced to North America and selectively prevent the importation of plants with the potential to be invasive. Efforts are underway to develop a national strategy for invasive species with consistent guidelines for preventing their spread. More research is needed on the economic and ecological impacts of certain species as well as research on effective control methods.

A recent "Plants Out of Place" conference in Eau Claire drew over 600 people to share their knowledge and concerns about plants that invade our lands and waters. Many of the participants also spent a day organizing a new statewide "Invasive Plants Association of Wisconsin (IPAW)." This membership-based organization will host a website, develop educational materials, draw up a comprehensive list of plants that are invasive in Wisconsin's wildlands and take on other tasks to deal with the many invasive plant issues. They also plan to work with industry groups such as nurseries and seed companies to find ways to contain invasive plants without blaming or unduly burdening any sectors of the economy. IPAW also will act as an umbrella organization to the many regional and county-based efforts to control invasive plant in the state. Persons interested in getting involved in IPAW or a local group can find more information on the group's temporary website at or by writing to IPAW at P.O. Box 5274, Madison, WI 53705-0274.

Sources for further information
Wisconsin Invasive Species

Information on many invasive plants from The Nature Conservancy

Wis. Manual of Control Recommendations for Ecologically Invasive Plants, May 1997. Bureau of Endangered Resources, WDNR, Box 7921, Madison, WI 53707-7921 (This manual is also available on the DNR website listed above).

Color brochures on garlic mustard and buckthorn are available at all University of Wisconsin County Extension offices.

S. Kelly Kearns manages the Plant Conservation Program for DNR's Endangered Resources program.

Twenty-four to watch for
These two dozen plants most commonly invade
natural areas in Wisconsin.
Plant nameForestsGrasslandsWetlandsLakes/Streams
Invasive Trees, Shrubs and Vines
Black locust (Robinia pseudoacacia) x x    
Common buckthorn (Rhamnus cathartica) x x x  
Glossy buckthorn (Rhamnus frangula) x   x  
Bush honeysuckles (Lonicera species x x    
Japanese barberry (Berberis thunbergii) x      
Multiflora rose (Rosa multiflora) x x    
Autumn olive (Elaeagnus umbellata) x x    
Oriental bittersweet (Celastrus orbiculatus) x x    
Invasive Herbaceous Plants
Garlic mustard (Alliaria petiolata) x      
Dame's rocket (Hesperis matronalis) x x    
Canada thistle (Cirsium arvense)   x    
Japanese knotweed (Fallopia japonica) x x x  
Spotted knapweed (Centaurea bierbersteinii)   x    
Leafy spurge (Euphorbia esula)   x    
Wild parsnip (Pastinaca sativa)   x    
Nodding thistle (Carduus nutans)   x    
Plumeless thistle (Carduus acanthoides)   x    
Crown vetch (Coronilla varia)   x    
Bird's foot trefoil (Lotus corniculatus)   x    
Purple loosestrife (Lythrum salicaria)     x x
Reed canary grass (Phalaris arundinacea)   x x  
Phragmites (Phragmites australis)     x  
Eurasian watermilfoil (Myriophyllum spicatum)       x
Curly-leaf pondweed (Potamogeton crispus)       x