Terrestrial Invasive Species
This is a list of the terrestrial invasive species that are currently in Calumet County. View more information about that species.
Many invasive non-plant species are in or near Calumet County as well. This list includes the gypsy moth, emerald ash borer, mute swans and wild boar to name a few. For additional current information on these and other non-aquatic invaders, visit the DNR website.
Funding from the Citizen-Based Monitoring Network paid for the mapping of wetland and terrestrial invasive plants in Calumet County. The mapping targeted species that are still in the stage of possible control or eradication in this county. Some of the invasive plants in the county, such as buckthorn, honeysuckle, Canada thistle, reed canary grass, and garlic mustard, are already so common that mapping would not have been productive.
There are many terrestrial invasive species in Calumet County that are not described here, including dame’s rocket, soapwort, yellow and white sweet clovers, ox-eye daisy, crown vetch, reed canary grass, Japanese barberry, Russian olive, and autumn olive to name a few. Listed are some of the plants that are of the greatest concern for this county at this time.
Both common and glossy buckthorns are common in woodlots throughout Calumet County. In autumn, when most trees have dropped their leaves, the green shrubs or small trees that remain green are buckthorns. They can reach 20 to 25 feet in height and 10 inches in diameter. Usually, they grow in a large shrub growth form, having a few to several stems from the base. The shrubs have to spread, loosely-branched crowns. Their bark is gray to brown, and both species of buckthorn are distinctive enough from native species to be identified at all times of the year once the characteristics of the bark have been learned. Buckthorn is spread by seeds, and care should be taken to avoid spreading this invasive plant. For additional information on common and glossy buckthorn, visit the DNR website.
Canada thistle is abundant in Calumet County, where many old fields have been taken over by this noxious weed. It is a 2 to 5 feet dioecious perennial forb with slender, grooved stems that branch only at the top. Stems become increasingly hairy as the plant matures. The leaves are smooth, oblong, tapering, and characterized by crinkled edges with numerous spines along the margins. It has numerous ¾ inch fragrant purple flowers from July to September. Canada thistle thrives in disturbed areas and in a wide variety of soils. It is abundant along roadsides and its seeds are frequently spread by mowing after flowering has begun. Canada thistle is considered a noxious weed under Wisconsin law and should not be allowed to go to seed. For additional information, visit the DNR website.
Common teasel is in the early stages of infestation in Calumet County. There are only a few patches, most of them off Lakeshore Drive, Joe Road and Cemetery Road. This plant can be contained and eliminated from Calumet County with a little bit of effort. Each plant can produce up to 2,000 seeds, so preventing every plant from going to seed is critical at this early stage of infestation.
Teasel grows as a basal rosette for a minimum of one year, then sends up a tall, flowering stalk and dies after flowering. The rosette stage varies according to the amount of time needed to acquire enough resources for flowering to occur. Teasel's unique small oval-shaped purple flower heads makes the plant easily identifiable when flowers or seed heads are present. Flowering stems may reach 6-7 feet in height. Common teasel blooms from June through October. For additional information visit the DNR website.
Cut-leaf teasel is beginning to become a serious problem in Calumet County. There are a number of significant patches of this invasive plant in the County, mostly in the Towns of Harrison, Brillion and Stockbridge. Each plant can produce up to 2,000 seeds, so preventing every single plant from going to seed is critical at this stage of infestation. As greater numbers of these plants spread in to Calumet County along major highways from the north, west and east, it is imperative that we stop the spread now.
Teasel grows as a basal rosette for a minimum of one year, then sends up a tall, flowering stalk and dies after flowering. The rosette stage varies according to the amount of time needed to acquire enough resources for flowering to occur. Teasel's unique small oval-shaped white flower heads make the plant easily identifiable when flowers or seed heads are present. Flowering stems may reach 6 to 8 feet in height. Cut-leaf teasel blooms from July through September. For additional information visit the DNR website.
Garlic mustard is very common in woodlots throughout Calumet County. It has invaded High Cliff State Park, Calumet County Park, the Brillion Wildlife Area, and many private woodlots as well. Garlic mustard is a cool-season biennial herb that ranges from 12 to 48 inches in height as an adult flowering plant. Leaves and stems have the distinctive odor of garlic when crushed. First year plants have a cluster of scallop edged leaves rising 2 to 4 inches in a rosette. Second-year plants produce a flowering stem with small white flowers. Garlic mustard is the only plant of this height in our woods with white flowers in May. Garlic mustard produces hundreds of seeds per plant. The seeds are believed to be dispersed on the fur of large animals such as deer and squirrels, by flowing water and very commonly by human activities.
Garlic Mustard is a rapidly spreading woodland weed that is displacing native woodland wildflowers in Wisconsin. It dominates the forest floor and can displace most native herbaceous species within ten years. This plant is a major threat to the survival of Wisconsin's woodland herbaceous flora and the wildlife that depend on it. Recent research has begun to show that garlic mustard can alter the chemistry of the soil, impacting all woodland plants. For additional information, visit the DNR website.
Bush honeysuckles were commonly planted ornamental shrubs in Calumet County. From these backyard and hedge plantings, the fruits were eaten by birds and the seeds carried off. Now there is honeysuckle in woodlots throughout Calumet County. Bush honeysuckles are easy to find in early spring when they begin leaf development one to two weeks before native shrubs. Honeysuckles are dense, upright shrubs, 3 to 10 feet in height, with shallow roots. The shaggy-barked older stems and branches of the shrubs are often hollow and easy to distinguish from other shrubs. Flowering occurs during May and June, and produces fragrant, tubular flowers arranged in pairs.
Honeysuckles vigorous growth inhibits development of native shrub and ground layer species and may entirely replace native species by shading and depleting soil of moisture and nutrients. The early leafing of these species is very damaging to spring ephemerals, such as our trilliums, spring beauties, hepatica and bloodroot, which have evolved to bloom before trees and shrubs have leafed out.
Keep an eye out for this invasive plant. There are only a few known patches of multi-flora rose in the wild in Calumet County. If you see this plant, eliminate it to prevent it from becoming a greater problem. Multi-flora rose is a dense spreading shrub with wide, arching canes and stiff curved thorns. Older plants may have a root crown diameter of 8 inches or more and can reach a height of 15 feet. The leaflets are nearly smooth on the upper surface and paler with short hairs on the underside. It blossoms in late spring with numerous white flowers. Each plant may produce up to 500,000 seeds. By law, multi-flora rose is considered a nuisance weed, and cannot be sold or propagated. It is also listed as "restricted" in NR 40. For additional information, visit the DNR website.
Spotted knapweed is found primarily in the dry, gravel soils of roadsides, parking lots, railroad beds and quarry areas in Calumet County. Spotted knapweed commonly grows to 3 to 4 feet, with the majority of stem growth occurring in June. Single thistle-like pinkish flowers are about ¾ inch in diameter. Spotted knapweed reproduces solely by seed, so the plants need to be controlled before going to seed. The flowers bloom from July through August, for a few days each. The heads reopen after about 20 days to scatter the nearly 1000 seeds per plant. Mow this plant in late June before it flowers and forms seeds. For additional information, visit the DNR website.
Common Tansy is not very common in Calumet County, yet. There are only a few known patches and they are still in the stage of being easy to control. Areas in Manitowoc and Brown County, however, have significant areas that are already densely overgrown with this invasive plant. Do not let it get out of control in Calumet County.
Tansy grows from two to five feet tall with yellow, button-like flower clusters. Common tansy is highly visible and can become common in roadsides, pastures, fields, prairies, and hedgerows. It grows in sunny, well-drained soils and blooms July to October. The plant gives off a strong fragrance when crushed. This perennial plant spreads via an extensive root system coupled with profuse seed production. Tansy especially favors disturbed soils along ditch banks, where water will quickly spread the seeds for miles. For more information, visit the DNR website.
Unfortunately, wild parsnip is abundant in Calumet County. This plant is being spread by seed along highway rights-of-ways and is moving onto adjacent private lands and fields. It is especially bad in some areas of the County. This invasive plant is a serious threat not only to our ecosystems, but to people who come in contact with it.
Caution! If sap from wild parsnip's leaves or stems gets on skin in the presence of sunlight, it can cause a severe, blistering burn that appears a day or two after exposure. Giant hogweed and cow parsnip cause a similar reaction, called phytophotodermatitis.
Depending on the habitat and growing conditions, individual flowering plants range from one to over four feet in height. Look for the large, coarse, flower spikes and yellow flowers from the first of June to the middle of July. It is best to mow this plant in late June, after the rosette sends up the flower spike and before it sets seed. Once the wild parsnip population builds, as it already has in Calumet County, it spreads rapidly. This species is an aggressive Eurasian weed. For more information, visit the DNR website.