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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

The towering invasive giant hogweed takes at least four to five years to mature. © Courtesy of Ian Shackleford
The towering invasive giant hogweed takes at least four to five years to mature.

June 2006

Green invaders on the horizon

Your help can keep troublesome new plants from taking root.

David J. Eagan


© Courtesy of Ian Shackleford
On the lookout | Stay watchful and report in
A rogue's gallery | What to do?
Contacts and links

Cupped hands and a muffled voice imitate a radio-dispatched call: "Plant alert! Attention! Invasive Fiddle-berry spotted in Sector 4-4-7! Repeat, Sector 4-4-7! Mobilize the SWAT team! There's not much time! Mayday!"

The mock alert teasingly was rendered by my teenage sons when I announced my new job working to control invasive plants. The irony is such an alarm truly is justified, though rarely heard, for some invasive species. Had the sirens gone off when the first purple loosestrife plants jumped from home gardens into Wisconsin wetlands, millions of dollars in control efforts might have been avoided.

While there's no such thing as Fiddle-berry, there are plenty of real plants whose appearance within our borders would be cause for alarm. Picture a grass that takes over the forest floor like a green flood, or a dense, floating mat of leafy plants covering acres of once-open lakes and backwaters. Such plants exist, but fortunately haven't found their way into Wisconsin – not yet.

Wisconsin's Invasive Plants of the Future project hopes alert volunteers will quickly recognize and report when new invasive plants arrive. Unlike most projects created after the fact to deal with invasive plants that are established problems, this initiative aims to find new invasions and nip them in the bud. This collaborative effort of the Wisconsin Department of Natural Resources and the Wisconsin State Herbarium is funded by a grant from the EPA Great Lakes National Program Office.

A team of plant experts helped choose the project's 15 target species. All are serious invasives in other states with similar climates. Half of the species are already present in Wisconsin, but in small or localized populations. The rest – as far as we know – are not here yet. And not surprisingly, there are plenty of other potential invaders that could pose a threat, but this list is a good starting point and more will be added in time.

On the lookout

Here are the "mean 15." You can also get a closer look at them online at Invasive Plants of the Future, or we can send you a brochure that you can keep in your car, boat or backpack to keep a lookout for these culprits as you travel.

New terrestrial invasives in uplands/lowlands

  • wineberry or wine raspberry (Rubus phoenicolasias)
  • Japanese hops (Humulus japonicus) [WI]*
  • black swallow-wort (Vincetoxicum nigrum) [WI]
  • pale swallow-wort (V. rossicum)
  • European marsh thistle (Cirsium palustre) [WI]
  • common teasel (Dipsacus fullonum subsp. sylvestris) [WI]
  • cut-leaved teasel (D. laciniatus) [WI]
  • giant hogweed (Heracleum mantegazzianum) [WI]
  • Japanese hedge-parsley (Torilis japonica) [WI]
  • field hedge-parsley (T. arvensis)
  • Japanese stilt grass (Microstegium vimineum)

New aquatic invasive plants

  • flowering rush (Butomus umbellatus) [WI]
  • hydrilla (Hydrilla verticillata)
  • European frog-bit (Hydrocharis morsus-ranae)
  • water chestnut (Trapa natans)

* [WI] notes plants already present in Wisconsin

Stay watchful and report in

It's one thing to know which plants to watch for, but quite another to make sure enough eyes are out there looking for them. That's why we ask for your help. Last year we launched the Wisconsin Weed Watchers program to train a statewide network of volunteers to spot these plants in local parks and natural areas, along roadsides and on private land. To date, more than 200 people from 40 counties have signed up and dozens of infestations have been reported.

These Weed Watcher reports have added greatly to our knowledge of where these target plants are spreading in the state. For instance, the easily-recognized teasels (both common and cut-leaved) have been running rampant in Mequon, along Black Earth Creek in Dane County, and in the Fox Valley. A small infestation was even found up north in Ashland. Thanks to many reports, we now know that teasel, Japanese hedge-parsley and European marsh thistle are much more widespread than originally thought. That's bad news, but it gives us a chance to act quickly to keep these early infestations from taking giant steps and expanding their footprint in the state.

A rogue's gallery

The following thumbnail descriptions and photos should help you get to know these 15 unsavory characters. If you think you've found a target plant, we provide advice on our website and in our brochure on eradicating each species, or you can call the project office. Control methods include hand-pulling and digging, mowing, herbicide application and prescribed burning. Your removal projects might be enough to get the job done, but don't hesitate to ask for help from local and state agencies, invasive plant specialists, and park or natural area "friends" groups.

If you are not 100 percent sure of a plant's identity, check with local experts, e-mail a photo or send a sample to the Wisconsin State Herbarium. Be sure to note the precise location using landmarks when you document your discovery, send a pressed specimen or forward photos. Report forms and instructions for making voucher specimens are also on the website.

Swallow-wort (black and pale)
Swallow-worts are perennial, herbaceous vines that readily invade both shady woodlands and sunny fields. They have smooth-edged, heart-shaped leaves in pairs along a slender stem. The vines trail on the ground or climb nearby vegetation rising to ten feet. A member of the milkweed family, swallow-wort makes slender pods whose seeds are topped with a downy plume. Over time, the plant can dominate the understory, shading out shrubs, wildflowers and other natives. The non-milky juice of the plant is toxic to insects, including Monarch butterflies that are fooled into laying eggs on the leaves. When larvae hatch and begin to feed, they soon die. Deer and other herbivores refuse to eat it. There are two known infestations of black swallow-wort: near Mukwonago in Waukesha County and around Potosi in Grant County.

Japanese stilt grass
This weak-stemmed, fast-invading annual grass can blanket forests, roadsides and river corridors. Its pale green leaves are relatively wide, 1-3 inches long and lightly hairy. A faint silvery stripe down the center of the leaf, caused by reflective hairs, is distinctive. It can reach five feet in height, but tends to grow one to three feet in a sprawling, mat-like manner. Narrow flower spikes appear in September and abundant seeds soon ripen. Stilt grass has become a huge problem in many eastern and midwestern states. It takes hold where soils are scoured or disturbed, such as along streambanks, floodplains, ditches and trails – spreading due to human activity and floods. Dead plants are a serious fire hazard. Although not yet known in Wisconsin, it is one of the most potentially troublesome future invasives.

Giant hogweed
Native to Russia, giant hogweed is found only at a few sites in northern Wisconsin's Iron County but is a widespread problem in the Upper Peninsula. A close cousin to our native cow parsnip, this mammoth plant towers 8-15 feet when in bloom. It takes four to five years to mature enough to flower, developing ever-larger leaves and a growing taproot. Its three-part leaves can be over five feet long. Both stems and leaves have short, bristly hairs rising out of distinctive purple bumps. It poses a serious hazard to people with sap that can cause blisters on skin exposed to sunlight. This is due to the same photo-sensitizing chemical found in wild parsnip, cow parsnip and angelica.

Teasel (common and cut-leaved)
In its first year, teasel forms a large, ground-hugging rosette of long leaves. A flower stalk rises in the second year, armed with sharp spines and topped with a distinctive flowerhead that looks like a porcupine on a stick. Older stands dominate infested areas, with first- and second-year plants choking off most other species.

The bristly dried head of this invasive is a popular addition in dried flower bouquets. © David J. Eagan
The bristly dried head of this invasive is a popular addition in dried flower bouquets.

© David J. Eagan

The bristly dried flower heads were once used to "tease" or raise the fuzzy nap on woolen fabrics, hence the name and origin. They now are a popular addition to dried flower arrangements, but commercial sale of these spiny bouquets spreads seeds and accelerates the invasion. Both species are present in the state.

Japanese hops
This climbing, annual vine resembles our native hops, but tends to form patches that engulf neighboring vegetation. Leaves are opposite and typically five-lobed, and the sprawling vines have sharp, backward-pointing barbs that allow it to climb nearby vegetation. It can be distinguished from other hops by leaf stems that usually are longer than the leaf length. The female flowers do not look like the "hops" familiar to the brewing industry. This plant prefers moist soils of lakeshores and river corridors. Currently, it is found in only a few southern and southwest counties.

Wineberry
With its arching and thorny canes, wineberry resembles our native red and black raspberries, but its stems are densely covered with both weak prickles and sharp thorns, giving a reddish appearance to this perennial shrub. Leaflets are relatively wide, with undersides covered in white, wooly hairs. Fruits are red and tasty, tempting landowners to ignore its expanding presence until too late. Seeds are dispersed by birds, and patches expand where the curved canes touch the ground and take root forming new plants. So far, no wild plants occur here.

Hedge-parsley (Japanese and spreading)
Japanese hedge-parsley is rapidly expanding its range in southern Wisconsin, though the nearly identical spreading hedge-parsley has not been seen. Dense patches of parsley- or fern-like compound leaves are evident in late spring, and the small white flowering umbels (that look like umbrellas) rapidly develop into clinging, hooked fruits. This invasive starts on the edges of forests and trails and spreads outward. Japanese hedge-parsley behaves as a biennial in our state. Seedlings form a rosette of leaves in the first summer. Plants remain green all winter, then develop flowering stalks the following spring.

Flowering rush
This is the only rush-like plant with showy three-petaled white or pink flowers atop a three-foot stem. It can grow as an emergent plant on shores and shallows or as a limp-leaved submersed plant in deeper water. Until it blossoms, its upright leaves resemble bur-reed and sedges. Flowering rush spreads mainly by underground rhizomes and via uprooted plants that migrate due to boat traffic, muskrat home-building and winter ice movement. It is found along the edges of a growing number of Wisconsin lakes and ponds, and is sold commercially as a water garden ornamental.

European marsh thistle
This prickly biennial is spreading fast in northern counties, and is easy to spot in low areas along roadsides in June. It has a distinctive compact cluster of purple flowers at the top of a relatively leafless stalk. All parts of the plant are fiercely armed with sharp prickles, which help distinguish it from our native marsh thistle whose stems are relatively thornless. First-year plants hug the ground like a spiny dandelion. Second-year flower stalks ripen into fuzzy seed heads, inviting the wind to spread the plant far and wide. Now that people are watching for this plant, it has been reported in many wetland types including pristine natural areas.

European frog-bit
Resembling a miniature water-lily with a showy, three-petaled flower, frog-bit is a free floating aquatic plant that prefers calm waters. It can blanket the surface of ponds and backwaters rapidly, spreading via runners and by plants that break away and form new colonies. Frog-bit survives cold winters by producing compact buds – called turions – that sink to the bottom in fall and rise when the weather warms. It is available for sale at garden stores and on the Internet, and may already be in Wisconsin, but no wild populations have been reported.

Hydrilla
Said to out-compete Eurasian water-milfoil (one of Wisconsin's worst aquatic invasives), hydrilla is a serious future threat to lakes and streams. It forms thick mats of submerged plants, clogging shallow lakes and harming boating and recreation. Narrow green leaves occur in whorls of 4-8 leaves along a slender stem. Tiny teeth along leaf edges and bumps on the underside of the midrib distinguish hydrilla from native waterweeds like elodea, which have smooth-edged leaves. Survival tactics include tubers which lodge in the mud forming compact buds that live over winter. Its stems are easily broken and can float to new locations. It becomes a ready hitchhiker on boat trailers and sport vehicles. Experimental plants have survived Minnesota winters but, so far, no infestations have been discovered here.

Water chestnut
No relation to the crunchy vegetable in Asian restaurants, this water chestnut is a leafy aquatic plant that forms dense surface mats hindering boats and swimmers. It roots to the bottom in shallow waters, with a vine-like stem that connects to a floating rosette of triangular, toothed leaves. Leaf stems have an air-filled bladder that keeps the plant afloat. Notorious for its rapid growth, water chestnut is also infamous for its foot-puncturing barbed fruits. Ouch!

What to do?

If you see one of these species or think you've found one but want an expert to confirm your identification, check out the website, call or request a brochure to get guidelines for submitting a sample.

Collect a good fresh or pressed specimen. Take detailed and close-up photos showing the plant's features like flowers, general shape, seed heads, leaf shape and arrangement. Then fill out one of the Invasive Plant Report Forms obtained from the website or the project office.

Send specimens and photos to: Invasive Plants Project, Wisconsin State Herbarium, 160 Birge Hall, UW-Madison 430 Lincoln Drive, Madison, WI 53706.

Pressed plant specimens (and even good photos of these invasives) sent to the herbarium will be identified by staff and may be entered into the state's permanent plant collection. If so, you will be listed as the collector and your name and record will appear (eventually) on the WISFLORA website. Most important, your scientific contribution adds to our growing knowledge of plant life in Wisconsin.

Each new growing season brings new opportunities for these unwanted weeds to invade Wisconsin. With your help, we have a chance to keep them from taking up permanent residence.

David J. Eagan coordinates the Invasive Plants of the Future program based in Madison.

Contacts and links
Invasive Plants of the Future
Information about target plants, Weed Watchers, plant reporting and more

invasbook.jpg - 11589 Bytes Invasive Plants Project
Send an e-mail, call with your plant questions or write for a brochure, or call (608) 267-7612. Write to: Wisconsin State Herbarium, UW-Madison, 160 Birge Hall, 430 Lincoln Dr., Madison, WI 53706

WISFLORA: Wisconsin Vascular Plants

Invasive Plants Photo Gallery