The “Bad Guys:” Invasive Plants
An invasive plant is one that threatens biodiversity—meaning the variation in species that determines the ability of a plant community to survive. The saying goes: “In diversity there is strength.” Remove the biodiversity (strength) from a living system, and you destroy it.
When invasives take hold in a new area, they displace other plants and outcompete with them for ground surface, sunlight, moisture, and nutrients. Where once there was a collection of beneficial plants, there is then just a monoculture, an unsightly mass made up of the foreign invader. Infestations of invasives can cause drastic changes in the landscape and can affect entire ecosystems.
Three of the most invasive plants along the wetlands of Glen Lake are Coltsfoot (Tussilago farfara, pictured above), Reed Canary Grass (Phalaris arundinacea) and its striped ornamental variety, Ribbon Grass; and Phragmites. All three of these invasives are particularly troublesome because of their ability to spread rapidly by rhizomes (similar to horizontal roots) and to form continuous and ever-expanding plots which wipe out everything else.
At Mama Bear Restorations, Inc., we are particularly concerned about Coltsfoot on the east shore of Glen Lake because it is a direct and imminent threat to the rare Michigan Monkey Flower (Mimulus michiganensis), an endangered plant that is critically globally imperiled and grows in no more than 15 places worldwide, all of them in Northern Michigan.
Coltsfoot, the Vicious Foreign Invader on Our Shores
"Coltsfoot is vicious stuff. If we don't get it contained at Glen Lake by the end of 2013, it's going to spread so badly that it'll make the garlic mustard and loosestrife invasions look like child's play in comparison."—Mama Bear
Mama Bear Restorations and the Glen Lake Associations are making an all-out effort to eradicate coltsfoot (Tussilago farfara) on the east shore of Big Glen Lake. We are anxious to eradicate and/or contain the coltsfoot incursion before it wipes out Glen Lake’s rare species, Michigan Monkey Flower (Mimulus michiganensis) as well as most other plants—native and non-native alike—along the shoreline, and additionally spreads into lawns and even agricultural fields. Unfortunately, the beaches and shorelines of Glen Lake are perfect homes for this unwanted alien.
How to Identify Coltsfoot
First identified at Glen Lake in 2008 by members of the Glen Lake Association and a National Park Service biologist, the dangerous plant almost certainly arrived on Glen Lake’s shores as a “hitchhiker” with landscape material such as trees. Since then, the invasion has rapidly moved along the shoreline, and it now grows from Harbor Island to Burdickville Hill (Inspiration Point). On several beaches the infestation is so serious that the growth is continuous for 200 linear feet or more in a swath ten feet wide and a foot high. Coltsfoot infestations spread in all directions by five feet or more each year.
In the very early Spring, yellow, solitary, dandelion-like coltsfoot flowers appear atop hairy, whitish, scaly/segmented stems poking up from the sand without leaves, sometimes through the snow. The flower stems look somewhat like asparagus. The flower buds are purplish on the outside when closed. The bright yellow flowers are usually about an inch wide. At about the time that the flowers begin to set seed, the leaves begin to appear. This means that late-blooming coltsfoot flowers and new leaves often appear together until eventually the seed heads open and disperse.
The fuzzy seed heads look like fluffy white balls containing parachute-like tufts resembling dandelions that have gone to seed. A single coltsfoot plant produces 4,000 to 5,000 seeds which typically either drop near the parent plant or travel by wind for four to eight miles. The seeds start the process of making new plants immediately.
How Coltsfoot Spreads
Although it is imperative to halt seed spread as much as possible by deadheading (removing the flowers), it is the creeping horizontal stems, called rhizomes, which are the paramount problem causing this foreign invader to spread so rapidly. The plant-producing rhizomes create extensive underground systems that spread both outward at various depths by as much as 18 feet and downward by as much as 10 feet. The very long, branched horizontal rhizome structure causes the common occurrence of coltsfoot plants popping up, seemingly out of nowhere, from a buried rhizome that appears to be far from other coltsfoot plants.
The coltsfoot rhizomes are extremely brittle and break off easily, and even the smallest bit of a rhizome will produce a new plant. Brittle rhizomes also make it easy for entire plants, with some rhizomes still attached, to break off from wave-pounded shorelines and travel to new beaches where they wash up and start new plants immediately. The only time it is safe to “dig” coltsfoot, is when one of these little plants is washing in or out without any attachments to the ground. In any other instance, digging will lead to an even more aggressive infestation and should never be attempted with plants whose root-like rhizomes have started to push into the sand.
Once the coltsfoot stems and leaves appear they continue to grow rapidly until a hard frost. By mid-summer, the heart-shaped leaves (which to some people look like the outline of a colt’s foot) are likely to be as much as five to seven inches wide and often almost as long. Coltsfoot leaves are usually slightly broader than they are long. The dark green leaves are smooth and waxy looking on the top, while the undersides are covered with wool-like hairs that often look white or gray when the leaves are blowing in the wind. The leaf stems, as well as the larger leaf veins are usually a purplish color. The plants grow close together in colonies, with their stalks and leaves forming a dense canopy that kills and/or prevents anything else from growing under or around it.
Coltsfoot, which has been used since pre-history for purported medicinal purposes (not supported by scientific studies), is native to Europe and Asia. It was brought to the North and South American continents by European settlers. Although still sold as an herbal remedy in the United States, studies have shown that coltsfoot contains liver-damaging alkaloids, a fact which led to the ban of coltsfoot sales in Germany.
Typically, however, it is invasive qualities rather than health issues, that land coltsfoot on various “Bad Guy” lists. Coltsfoot is on several invasive species lists for areas east of the Mississippi. It has been declared invasive and banned in Connecticut; illegal to take it into Oregon; prohibited in Massachusetts; and classified as a noxious weed in Alabama.
A relatively new and unwelcome plant in the State of Michigan, coltsfoot locations currently are being reported and can be expected to be on State and Regional invasive species lists in the near future.
How to Eradicate Coltsfoot
Eradicating coltsfoot is tricky. The first technique—one which is necessary as long as any plants remain in an area—is removing all blossoms when they appear in the Spring. Blossom removal, called deadheading, must be repeated on a weekly basis until the blossoms stop appearing. Once deadheading is completed and the leaves have appeared, eradication requires total root and rhizomes kill, not just killing of leaves.
Attempting to eradicate coltsfoot by digging will only make the infestation worse because bits of rhizomes inevitably remain in the soil and produce multiple new plants. Any other types of mechanical removal—weed whacking, for example—have the same result as digging, which is to make a bad situation much worse.
The solarization technique—in which patches of coltsfoot are covered with heavy pond liner for at least one full growing season or longer—appears to be effective but is unsightly and requires patience. It can be expensive both in terms of labor and materials.
Eradication of coltsfoot with herbicide is known to be effective in almost all instances. Eradication can be especially challenging at Glen Lake where plants often grow close to the water’s edge, which means that a special product must be used—one that is approved by the US EPA for use near or over water. The herbicide cannot be sprayed, but rather must be applied by hand using what is usually called the wicking method or glove-in-glove method. Moreover, the lake side of the herbicided plants often must be shielded from wave splash.
Coltsfoot Eradication on Glen Lake in Leelanau County
In mid-summer 2012, Mama Bear spearheaded formation of a community effort to hire a licensed applicator on a group contract. As a public service, Mama Bear Restorations staff provided onsite monitoring and supervisions of the herbicide application process. It is possible that similar groups will be formed from time to time, possibly for treating coltsfoot as soon as September 2012.
Some landowners want to treat the coltsfoot on their property. In almost all cases, Mama Bear discourages landowners from attempting to treat their own coltsfoot for at least three reasons: 1) There are no pre-mixed herbicides available that are safe to use near or over water (Round Up is not safe for shoreline use.); 2) Landowners do not know how to apply herbicide without spraying it; and 3) Our monitoring indicates that when landowners treat their own coltsfoot, they almost inevitably miss some of the plants, thus considerably lessening the effectiveness of the attempted treatment.
Written and researched by Jody Marquis, Founder and CEO, Mama Bear Restorations, Inc.