Montana Weed Identification

This field guide from the Montana Weed Control Association is designed to help you identify Montana’s 35 state listed noxious weeds and regulated plants. Each plant review includes the photos and the 10 characteristics defined to your right.

If you believe you have found a noxious weed, contact your county weed district. They can help you with a management plan, offer best practices on control and eradication and, in some counties, they provide cost-share programs to assist you with management.

Here is a list of the Montana weed control districts that have governance and regulatory authority in your county.

You can find photos and descriptions of Montana invasive and noxious weeds here

Rush Skeleton Weed

Common Tansy

Canada Thistle

MSU Extension Service

Common tansy (Tanacetum vulgare)

By Noelle Orloff, Associate Extension Specialist and Schutter Lab Diagnostician

Common tansy is an exotic perennial forb in the Asteraceae family that is on Montana’s noxious weed list. It inhabits higher moisture, disturbed soils, and can be found in places like meadows and riparian areas as well as along roadsides, ditches, and railroad tracks. Common tansy was introduced to North America from Europe for medicinal use and as an ornamental plant.

Identification When common tansy is flowering it is relatively easy to recognize. Flowering heads resemble yellow buttons, and are arranged in flat-topped, compact clusters. Leaves are alternately arranged and pinnately compound. They appear “feathery,” with leaf segments having sharply lobed and toothed edges. Stems tend to be somewhat reddish in color. Common tansy has aromatic foliage, and it also has white sap. This species often grows around three or four feet tall.

Biology, Ecology, and Impacts

Common tansy is aperennial species that reproduces mainly by seeds, but it also spreads by creeping rhizomes that allow it to form dense patches. Dense stands decrease forage availability for grazing animals. This species is considered toxic to livestock and humans if enough is consumed. Common
tansy contains thujone, a toxin that can cause miscarriages, convulsions, stomach pain, and skin irritation. In large
enough quantities it has been reported to cause abortion in cattle and is also suspected to affect goats and horses. It is
relatively unpalatable, and for this reason cases of livestock poisoning are rare.

Common tansy management is best undertaken with an integrated approach. For mechanical control, mowing is not generally thought to be effective in controlling established plants, but mowing just before flowering may decrease seed production. Handpulling may be useful in very small, newly established patches, but make sure to wear gloves and long sleeves.

Finally, encouraging a stand of competitive vegetation and limiting disturbance can help slow the spread of this species and limit its encroachment into new areas.

See the MSU Extension publication Common tansy (Tanacetum vulgare) for more details about common tansy and its management.

Blue Weed

Dyer's Woad

Managing common Mullein

In midsummer, the tall flower stalks of common mullein begin to poke up, making this common weed highly noticeable in the road cuts and waste areas where it thrives.

Native to Europe, northern Africa and Asia, it was probably introduced to North America several times as a medicinal herb. In the mid‑1700’s it was used in Virginia as a piscicide (fish poison). It spread rapidly and had become so well established by 1818 that a flora of the East Coast at that time described it as a native. It had reached the Midwest by 1839 and became widely naturalized on the Pacific Coast by 1876. Today common mullein is distributed throughout the U.S. and Canada wherever the growing season is at least 140 days and rainfall is sufficient (50-150 cm), especially on dry sandy soils.

GOATS FOR MULLEIN CONTROL

Goats are a viable option for controlling mullein. Goats eat the flowering rosette as it appears on the soil, and will eat the large seed heads once the plant has gone to seed.

Common mullein is typically found in neglected meadows and pasture lands, along fence rows and roadsides, in vacant lots, wood edges, forest openings and industrial areas.

This plant, also known as wooly mullein, is an herbaceous biennial or short-lived perennial with a deep tap root. In the first year plants are low-growing rosettes of felt-like leaves. The whorl of leaves emerge from the root crown at the soil surface. The bluish gray-green, oblong to lanceolate leaves are 4-12″ long and 1-5″ wide, and are densely covered in hairs. Vernalization (exposure to cold temperatures) is required to induce flowering the following spring.

The fruit is a rounded capsule that splits into two valves at maturity. Each contains dozens of tiny brown seeds. The six-sided seeds are pitted and rough with wavy ridges and deep grooves. Individual plants produce 200-300 seed capsules, each containing 500-800 seeds, so that 100,000‑240,000 seeds are produced per plant. Most seeds fall within a few feet of the parent plant, falling from the capsules when the flower stalk is moved by wind or a large animal. There are no adaptations for long distance dispersal.

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Common mullein just before growing its large stalks. BELOW, a goat eats a mullein seed head.