European coltsfoot (Tussilago farfara) March 2018 Weed of the Month

Just added to the Washington State Noxious Weed List in 2018, European coltsfoot (Tussilago farfara) is still new to many of us in the noxious weed world. However, this interesting species has been used as a medicinal plant in China and Europe for centuries, and is still commonly cultivated in medicinal gardens. It has been used to treat a wide range of ailments from respiratory diseases to wounds to inflammation. Unfortunately, European coltsfoot does contain toxic pyrrolizidine alkaloids that can cause liver damage. The plant shouldn’t be used as forage for livestock or used medicinally without medical oversight and careful monitoring.

European coltsfoot flowers in late winter to early spring on stems that appear to be leafless (but actually have small, clasping, scale-like leaves). The flowers are bright yellow and look a lot like dandelions, but on really stout stems.

Tussilago farfara flowering stems Three Forks Park MBelow

European coltsfoot flowering stems in early April. Photo by Matt Below.

After the flowers fade, larger, more obvious leaves start emerging on separate stems. Technically these leaves are all basal on long petioles coming straight from rhizomes, but you don’t need to know that to recognize them.

These separate leaves are broad and tend to lay horizontally raised up on top of tall, stout stems. The shape is somewhat heart shaped or round in outline but angled along the periphery as if someone had cut off the rounded edges of the leaf. The tops of the leaves are green and the undersides are whitish, covered with felted hairs.

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European coltsfoot leaves in August. Photo by Patrick Sowers.

The growth pattern of the flowering stems emerging first and leafy stems later is one of the most conspicuous features of this plant. However, you will see the same pattern of flowers before leaves on the coltsfoot species native to Washington, Petasites frigidus, as well as non-native species of Petasites that are sometimes used in gardens (and that occasionally escape as well).

Our native coltsfoot has white flowers not yellow so that makes distinguishing it easy this time of year. The leaf shape is also different, but that can be more difficult to determine if the plants aren’t side by side. See the UW Burke Museum Image Collection for excellent photos of our native coltsfoot. Although they look different, the two species are similar enough in overall growth form and habitat that the first time I spotted European coltsfoot I thought it was just a different looking form of our native species. I was very sad when I found out the truth!

The cause for concern about European coltsfoot comes from its tendency to move into disturbed areas such as crop fields and riparian habitats and then become dominant over other plant species. It thrives on disturbance to the point where it actually does better in a cultivated agricultural field than in a field that is left fallow. In Europe where the plant is native, it is still a troublesome weed in agricultural systems, especially organic farms, where it is extremely difficult to control once it becomes established.

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European coltsfoot escaping out of a garden bed. Photo by Karen Peterson.

Another key area where European coltsfoot creates problems is riparian or wetlands systems that are naturally disturbed, or where other invasive vegetation is removed, allowing an opening for it to get started. On the Snoqualmie River at Three Forks Natural Area there is a large infestation of European coltsfoot in area where there has been considerable natural disturbance through flooding and active bank erosion. The infestation has grown over the past decade, likely helped by the removal of large amounts of knotweed from the same area which has opened up new areas for it to invade.

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European coltsfoot has spread over a large area in Three Forks Natural Area on the Snoqualmie River. Annual flooding and removal of other invasive weeds has helped the population move and expand. Photo by Patrick Sowers.

Perhaps the most alarming feature about European coltsfoot is how easily it spreads through fragmentation of rhizomes. It has been spread to new farm fields carried on equipment, floods and erosion have moved fragments along water ways, and rhizome fragments have been spread in contaminated gravel and rock from gravel pits and quarries. Also, the rhizome fragments are quite durable and can survive flooding, deep burial and significant mechanical disturbance such as found in a quarry, cultivated field or a flooded river system.

Tussilago farfara emerging along an eroding bank

European coltsfoot leaves emerging along an eroding bank of the Snoqualmie River. Photo by Matt Below.

Tussilago farfara Three Forks Park MBelow

European coltsfoot leaves emerging along an eroding bank of the Snoqualmie River in early April. Photo by Matt Below.

Tussilago farfara clump in hand Three Forks Park MBelow

European coltsfoot clump in hand in early April. The brittle rhizomes makes it easy for this plant to spread along rivers. Photo by Matt Below.

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European coltsfoot is all over this aggregate pile. Contaminated gravel and rock is one of the common ways this plant spreads to new location. Photo by Tricia MacLaren.

If being invasive and spreading so easily by fragments isn’t enough to alarm you, European coltsfoot is also very difficult to control. Small patches can be dug up, but the rhizomes break off easily making this method not very effective and requiring lots of follow up work. A small roadside population of European coltsfoot in Mt. Rainier National Park was carefully dug up repeatedly during the year it was first found but plants still remained the following year.

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Tussilago farfara growing at Mt. Rainier National Park along a road. Photo by Crow Vecchio 2016

Even chemical control is no sure thing with this plant. The large infestation at Three Forks Natural Area has been treated chemically with aquatic approved triclopyr and imazapyr with only partial success. Small patches are somewhat reduced, but the large patches are still about the same size. There seems to be a lot to learn still on timing and other factors.

There is some good news though. European coltsfoot seems to be less dominating where other vegetation is well-established and there is less disturbance. In crop fields, reduced frequency of cultivation and allowing fields to go fallow for a time may be what is needed. In natural systems, the goal should be to establish healthy competitive vegetation that can fend off invasions better (always a good idea!). Particularly in riparian areas and other disturbance-prone systems, after removing invasive plants it is always wise to monitor for secondary invasions and act quickly to prevent problem species such as European coltsfoot getting a foothold.

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Natural and human disturbance in riparian areas such as this allow for openings that European coltsfoot quickly fills in. Establishing native trees and other vegetation helps reduce weeds in the long run. Photo by Sasha Shaw.

Although we have a few records of European coltsfoot in King County, we expect to find more now that we are looking more. We would really appreciate any help we can get in locating populations of this species so we can work with the landowners or agencies to act quickly to stop it from spreading.

Report infestations online or contact us through our email or phone us at 206-477-9333. Outside of King County, please contact your local noxious weed program or in Washington contact the state noxious weed board, or use the handy EDDMapSWest App on your smart phone.

For more information about European coltsfoot, including identification and control, please visit the Washington State Noxious Weed Board website or read their excellent Written Findings on Tussilago farfara.

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It is important to map all populations of European coltsfoot and report it to someone who can help stop it from spreading more. Photo by Sasha Shaw.



Categories: Weed Control, Weed Identification, Weed of the Month

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