Category Archives: Invasive Plants

Wild Parsnip

What is wild parsnip? Wild parsnip (Pastinaca sativa) is an aggressive Eurasian member of the carrot family that grows in sunny areas and tolerates dry to wet soil types. It is often found along highways, in prairies or bordering farmed fields. The plant spreads primarily by seed. Sap from the plant can cause phytophotodermatitis, a light sensitive reaction on your skin. If the juice from broken stalks, leaves or flowers contacts your skin and then is exposed to sunlight, a skin rash will result 24-48 hours later. Symptoms range from slightly reddened skin to large blisters. The blisters may produce a sensation similar to a mild to severe sunburn. The blisters do not spread or itch, as poison ivy rashes do, but they are uncomfortable and leave brown scars that last for a number of months to two years. See your doctor if you develop burn symptoms.

A wild parsnip plant.
A wild parsnip plant.

What does wild parsnip look like? At maturity, wild parsnip is about four to five feet tall. It bears many large flat clusters of yellow-green flowers on a thick stem. Flowers appear from the first of June through July in southern Wisconsin. Seeds form around the end of July. The plant will often have both flowers and seed capsules at the same time. Seeds are flat, oval and about the size of a sunflower seed. After flowering and producing seed, the plant turns brown and dies. The plants have a rosette of basal leaves, as well as leaves arranged alternately on the stem. The leaves are branched into leaflets and have heavily toothed margins. The plant can be confused with prairie parsley (Polytaenia nuttallii), an endangered native species in Wisconsin. Prairie parsley has sparse, light yellow flowers, and long leaves branched into leaflets with few teeth.

How can I control wild parsnip? Prevention is the best way to control wild parsnip. When wild parsnip is first detected in an area, it can be cut below ground level with a sharp shovel. Be sure to wear long sleeves, long pants and gloves when working with plants. Also, try to work after sunset so that exposure to sunlight does not occur. Plants can also be pulled by hand, if you wear protective gloves. If the wild parsnip population is fairly large, you may use a brush-cutter just after peak bloom and before the plant sets seed. Remove all the cut material. A few weeks later, repeat the treatment to prevent plants from re-sprouting. Treatments may need to be repeated over several years. Herbicides containing the active ingredient glyphosate are also effective against wild parsnip. In high quality natural areas such as prairies, the Department of Natural Resources recommends burning the site and then applying spot treatments of a 1-3% glyphosate solution to wild parsnip rosettes if they re-sprout after burning.

For more information on wild parsnip: See the DNR publication ER-090-97 – “Wisconsin Manual of Control recommendations for Ecologically Invasive Plants”, or contact your county Extension agent.


Purple Loosestrife

What is purple loosestrife? Purple loosestrife (Lythrum salicaria) is a fast-spreading, tall Eurasian plant that grows primarily in wetlands and ditches, but can invade home gardens. It was introduced from Europe in the 1800s as a perennial garden plant. Although this plant or its cultivars are sometimes still sold in garden centers, it is illegal to sell, distribute or cultivate this plant or its seeds in Wisconsin. Purple loosestrife has a wide tolerance of environmental conditions and spreads by seed as well as by aggressive rhizomes. Purple loosestrife can produce more than two million tiny seeds per plant. Seeds are easily spread by wind and water, remaining viable in the soil for many years. The plant also has a thick taproot with fibrous rhizomes that form a dense mat, making it difficult to remove. In addition, the insects and diseases that keep the plant’s population in check in its homeland are not present in North America. These factors allow purple loosestrife to spread rapidly through wetlands and other areas where it chokes out other desirable native vegetation and eliminates open water habitat that is important to wildlife.

Purple loosestrife.
Purple loosestrife.

What does purple loosestrife look like? Purple loosestrife usually grows to a height of 3 to 7 ft., but it can grow as tall as 12 ft. It can live for many years, usually becoming tough and fibrous at the base. Purple loosestrife has narrow leaves that are arranged opposite each other on the stem. Each plant can produce from one to 50 flowering stems. Flowers are magenta pink and have five to seven narrow petals. Purple loosestrife may bloom from July all the way into early September.

How can I control purple loosestrife? Prevent the spread of purple loosestrife by inspecting equipment, boats, shoes, and other items that have been in contact with purple loosestrife-infested areas. Small infestations can be removed with a shovel. Be sure no portions of roots or stems remain. Glyphosate-containing herbicides are recommended for chemical control. Spray the foliage with a solution containing 1% active ingredient, or apply to cut stems in a solution containing 3-10% active ingredient. Herbicides containing the active ingredient triclopyr, formulated for water dilution are also effective. Biological control using insects that solely feed on purple loosestrife are also proving effective (see box below for more information). All control methods will likely need to be repeated for several years. Encourage your community to scout for and remove any purple loosestrife in your area.

For more information on purple loosestrife: Access the Wisconsin DNR website (, write to: Purple Loosestrife Project, 101 S. Webster St., WY/3, PO Box 7921, Madison, WI 53707-7921, email, call (608)-266-2554, or contact your county UW-Extension agent.

Invasive Phragmites

What is invasive phragmites? Invasive phragmites (Phragmites australis subsp. australis) or common reed is a tall, perennial grass that aggressively colonizes and forms dense stands in freshwater wetlands.

Invasive phragmites forms a grayish-purple, feather-like flower head (left) and leaves that are rough-margined, flat and gray-green, with sheaths that wrap tightly around the stalk (right).
Invasive phragmites forms a grayish-purple, feather-like flower head (left) and leaves that are rough-margined, flat and gray-green, with sheaths that wrap tightly around the stalk (right).

It is found throughout North America, but is most common along the east coast of the US and in the Great Lakes region. In Wisconsin, invasive phragmites can be found along shorelines of lakes, exposed lake beds, marshes, streams, swamps, rivers, roadside ditches, heavily disturbed sites and other low, wet areas. Invasive phragmites harms the environment by reducing wildlife habitats, decreasing plant diversity, and altering water levels by trapping sediments. In addition, invasive phragmites can be a fire hazard. Stands along roadsides can obstruct the view of drivers, leading to automobile accidents, and stands along shorelines can reduce property values by blocking lake views, and restricting access for swimming, fishing and hunting. Invasive phragmites is a subspecies of a Eurasian form of the grass (known as “haplotype M”) that is believed to have been accidentally introduced into North America in the early 19th century. A native phragmites (Phragmites australis subsp. americanus) once grew abundantly in North America, but currently is rare because it has been displaced by invasive phragmites.

What does invasive phragmites look like? Invasive phragmites plants grow up to 15 feet tall and form grayish-purple, feather-like flower heads in late July. These plumes are five to 16 inches long and develop dark brown seed heads at maturity. Invasive phragmites leaves have sheaths that are wrapped tightly around the stalk, and leaf blades that are rough-margined, flat, and linear in shape with a gray-green color. At the base of each leaf blade, a fringe of hairy ligules is present with no auricle clasping the stalk. To distinguish native phragmites from invasive phragmites, closely observe the plant’s stalk. Stalks of invasive phragmites plants are rigid, rough, dull, tan in color, and hollow inside. Native phragmites plants develop non-rigid, smooth, lustrous reddish-colored stalks during the growing season.

How does invasive phragmites reproduce and spread? Invasive phragmites primarily reproduces vegetatively by producing below-ground rhizomes and above-ground stolons. Although invasive phragmites produces seeds, these seeds are rarely able to germinate to form new plants. The rhizomes of invasive phragmites are stout, scaly, and grow actively during late summer through early winter forming a dense underground mat. Each node of the rhizomes can produce a new bud in the fall that will remain dormant during winter and produce a new plant in the spring. Rhizomes can grow as much as six feet per year and eventually reach more than 60 feet in length in an established stand. They can also penetrate more than six feet deep into the soil. Human actions like dredging and disking in wetlands, as well as natural actions (e.g., wave movement) can break the rhizomes into many pieces and help disperse the plant to new locations.

How do I control invasive phragmites? Small patches of invasive phragmites in home backyard settings can be controlled using the bundle, cut and chemical treatment method. First, bundle canes together tightly at waist height with twine. Next, cut the canes just above the twine. Finally, immediately treat the cut ends of the canes with an appropriate glyphosate product labeled for the site where the invasive phragmites is growing. If the patches are in standing water or in a wet area, use a glyphosate product labeled for aquatic use (e.g., Rodeo®) and be sure to obtain a permit from the Wisconsin DNR before treating the patch. For dry land sites, terrestrial glyphosate products (e.g., Roundup®) can be used and no permit is required. Herbicides solutions need to contain at least 20% glyphosate to be effective. Always read the label on the herbicide that you select before applying the product to ensure that you apply the herbicide in the safest, most effective manner possible. The ideal time to bundle, cut and chemically treat invasive phragmites is from late July until September before the first killing frost occurs. Once plants have been treated with an herbicide, allow at least two weeks for the canes to die. Once canes have died, they can be mowed using a small mower or weed whip. In wet sites, wait until the ground is frozen to mow. Bag the mowed plants in a clear garbage bag, label the bag “INVASIVE PLANTS” and dispose of the plants in a landfill. DO NOT compost this material. Evaluate the success of your treatment the following growing season. If there is any re-growth, treat with a foliar application of glyphosate (again with proper permitting and using the proper site-specific product). Studies have shown that repeated mowing of an invasive phragmites stand without herbicide treatment is an ineffective control strategy. Invasive phragmites rhizomes simply re-sprout, and repeated mowing actually increases the density of the invasive phragmites patch. For large-scale management, please see “A Landowners Guide to Phragmites Control”, available at:
or contact your local Wisconsin Department of Natural Resources (DNR) representative for advice.

For more information on invasive phragmites: Contact your county Extension agent.

Garlic Mustard

What is garlic mustard?  Garlic mustard (Alliaria petiolata) is a European woodland plant introduced to North America by early settlers for its culinary and alleged medicinal qualities.  In North America, European insects and diseases that control the plant’s population are not present.  Garlic mustard starts growing earlier in the season than our native plants, and outcompetes them.  It also produces large quantities of seed.  For these reasons, garlic mustard spreads rapidly in wooded areas, forming tall, dense stands that smother native wildflowers, and native tree and shrub seedlings.  It can overrun a forest floor in a few years, destroying a previously healthy ecosystem by eliminating many plant species.  In addition, animals, birds and insects that depended on a diversity of plant species for food and shelter can then no longer live in the infested area.

Garlic mustard: First year rosette (left), second year plant with flowers (middle), and mature plant with seed pods (right).
Garlic mustard: First year rosette (left), second year plant with flowers (middle), and mature plant with seed pods (right).

What does garlic mustard look like?  Garlic mustard is a biennial plant with a two-year life cycle.  The first year, it forms a rosette of round, scalloped-margined leaves that stay semi-evergreen through winter.  The second year, it sends up a flower stem with triangular toothed leaves that bears tiny white flowers with four petals.  The plant dies after producing long narrow seedpods.  At maturity, garlic mustard plants may be 3 to 4 ft. tall and bear up to 500 seeds per plant.

How can I control garlic mustard?  Repeat any control method for several years since garlic mustard seeds can survive in the soil for up to 7 years.  Hand-pull small infestations, but do not compost the plants because most compost piles do not get hot enough to kill the seeds.  Dispose of pulled plants by burying deeply in an area that will not be disturbed, or landfilling.  Call the Bureau of Endangered Resources at 608-266-7012 if you need permission to landfill garlic mustard.  To burn collected plants, burn them while still moist, because dried garlic mustard seedpods can burst open and spread the seed.  If you use an herbicide, spray early in spring or late in fall, because our native plants are dormant at these times, but garlic mustard is still green and vulnerable to sprays.  A 1-2% solution of a glyphosate-containing herbicide is very effective.  Glyphosate is a nonselective herbicide, so avoid spraying nontarget plants.  Read and follow all label directions on the herbicide product.  Encourage your community to scout for garlic mustard in your area and remove it, if found.

For more information on garlic mustard:  See UW-Extension brochure #2000 – “Garlic Mustard, a Major Threat to Wisconsin’s Woodlands”, or contact your county Extension agent.

Dame’s Rocket

Invasive Plant Series What is dame’s rocket? Dame’s rocket (Hesperis matronalis) is a Eurasian biennial belonging to the mustard family. It was introduced to North America in the 1600’s and has naturalized itself in moist, wooded areas, but can also invade open areas. It may be sold in garden centers as a perennial and is often included in “wildflower” seed mixes. The plant’s three-month-long blooming period and ability to set abundant seed have contributed to its spread, as well.

Dame’s rocket leaf.
Dame’s rocket leaf.
Dame’s rocket flowers (enlarged).
Dame’s rocket flowers(enlarged).
Dame’s rocket seed pods.
Dame’s rocket
seed pods.

What does dame’s rocket look like? Dame’s rocket bears loose clusters of attractive, fragrant, pinkish-purple to white four-petaled flowers on 2 to 4 ft. stems. Flowers are produced from May–August, and the plant can produce seeds and flowers on any flower cluster at the same time. Leaves are slightly hairy and lance-shaped with toothed margins. Leaves are arranged alternately on the stem, and the basal rosette of leaves remains semi-evergreen through winter. The plants spend their first year as a rosette of basal leaves. They produce a flowering stem the second or third year, bloom, and then die. Seed pods are about 11∕2 inches long and very narrow. Dame’s rocket is often confused with garden phlox (Phlox paniculata), because the flower colors, clustered blooms and bloom time are similar. However, garden phlox has flowers with five petals (dame’s rocket has four) and opposite, untoothed leaves (dame’s rocket has alternate, toothed leaves).

How can I control dame’s rocket? Check any “wildflower” seed packets you may purchase to ensure that they do not contain dame’s rocket seeds. You can cut the flower heads off established plants after bloom so the plants do not set seed, or hand pull the plants. If plants are pulled while in bloom, do not compost them, as the seeds can still ripen and spread. Bag the plants for landfilling, or burn them. Do not allow the plants to dry before burning, as seedpods may burst open and spread seeds when dried. If appropriate, burn infested areas where allowed. Finally, glyphosate-containing herbicides can be applied in late fall when native plants are dormant, but the dame’s rocket basal leaf rosettes are still green and vulnerable to sprays. Avoid getting the herbicide on other plants. Repeat control measures for a few years until seeds in the soil are depleted.

For more information on dame’s rocket: See the DNR publication ER-090-97 – “Wisconsin Manual of Control recommendations for Ecologically Invasive Plants”, or contact your county Extension agent.