Tansy ragwort identification and control

Why it's a problem

Tansy ragwort is an invasive, toxic biennial (2-year life cycle) weed from Europe most often found in pastures and along roads and trails. Tansy ragwort was first seen in seaports on the east coast in the early 1900's and is often spread in contaminated hay.

Although animals tend to avoid it, eating it can sicken or even kill cattle, horses, some goats, pets, and people. The highest risk is after the plants have been cut or mixed in with hay, because the plants are not as bitter then and just as toxic. Despite efforts to control it, tansy ragwort is widespread in the Pacific Northwest. Plants produce thousands of seeds that can survive in the soil for 10 or more years.

Plant description

Tansy ragwort takes 2 years to mature, so plants will look different depending on which stage they are in.

In all stages of growth, leaves are often described as “kale like”. Leaves are green and ruffled or lobed. Young leaves tend to be a darker green.

First year plants are in the rosette stage, a circular arrangement of leaves growing close to the ground. Younger plants often have purplish stems.

Second year plants are leafy, flowering, 2- to 4-foot-tall stalks. Leaves are dark green on top and pale green underneath. The main stem is stout and near the tops of the plant it branches out to form many smaller stems. In the summer, the plant has dense clusters of bright, yellow, daisy-like flower heads with a yellow-orange center. Flowering usually starts in June and can continue into early November or until a hard frost.

As the plant begins to produce seeds, the mature plant dies back the leaves and stems will dry out, turning yellow and then brown. Plants can regrow from old root systems, sometimes “creeping” and producing multiple plants. Mostly they reproduce by seed from the dying plants. Ragwort that has been mowed or broken off can regrow from the roots and flower again the same year.

Seeds typically start to form by mid-August, and earlier in hot, dry locations. It is best to control these plants before they produce seeds as each plant may produce as many as 150,000 small fluffy white seeds that escape easily when disturbed. Seeds can survive for as long as 15 years in the soil.

Be aware of look-alike plants

Tansy ragwort is often confused with an even more widespread weed called common tansy (Tanacetum vulgare), a European species and somewhat toxic, but not generally eaten by livestock because of its strong odor and very bitter taste. The two "tansies" are most easily told apart by their flowers. Tansy ragwort has daisy like flowers with outer petals and common tansy has button-like blooms with no petals.  

Common groundsel

Common St. Johnswort

Western goldenrod

Who's who? Noxious weeds and their look-alikes

When in doubt, take photos and share them with us or report them on iNaturalist.

What to do if you find it

Please notify us if you see tansy ragwort where horses or other animals are grazing or along roads. Property owners are required to control tansy ragwort on lands that they manage. 

Our program staff can provide you with site-specific advice on how best to remove it. We map all known locations of regulated noxious weeds to help locate new infestations in time to control them.

Control methods

We recommend using a combination of methods to control noxious weeds. In areas with few weeds, it is important to act quickly before they become harder to control. Make a long-term plan as it often takes several years to get rid of most weeds. Start in the least infested areas first and then move into more heavily infested areas. Tansy ragwort reproduces via seed, so we strongly recommend control before seed set, typically in August. The best time to control it is before the flowers open. Once you see yellow, seeds are not far behind.

For more in-depth control information, read Best Management Practices (BMP) for tansy ragwort (205KB)

Manual Control

Seedlings and rosettes can be dug up as soon as they appear. This is easiest in fall and spring when soils are softer but can be done anytime.

Once ragwort begins to bolt and flower it can be hand pulled. Be sure to remove as much of the root as possible.

Plants can grow back from roots left in the ground. Flowers will go to seed even after digging or pulling, so bag and discard flowers stems. Best to pull/dig out plants before the soil gets hard and dry, if possible.

Mechanical Control

Mowing can be a way to suppress tansy ragwort, only if repeated at least 3 to 4 times during the growing season or whenever flowers appear.

Be aware that tansy ragwort that is mowed a lot can live for many years, growing very large root systems. Plants that are only mowed once or twice in a season will flower again on shorter stalks. Mowing is best when combined with other control methods.

Tilling may be effective for large areas but is likely to bring more seeds up to the soil surface where they can sprout. Reseeding or planting after tilling is ideal. Do not mow or till if tansy ragwort is in seed.

Cultural control

Good pasture/land management can help keep out unwanted plants. Re-seeding or planting an area that has been cleared of ragwort is highly recommended. Fast growing pasture grasses or other desirable plants can be good competition for weed seeds and can reduce the amount that grows in the following years.

Biological control

There are 2 approved biological control insects used in Washington. These insects only feed on tansy ragwort. They include a flea beetle, Longitarsus jacobaeae, and a seed head fly, Botanophila seneciella. Seed head fly larvae feed on the developing seeds of tansy ragwort. Look for tansy flowers where the center of the flower is covered in tiny bubbles. Flea beetles activity is easiest to see in the fall. Look for rosettes that are full of small holes.  Both insects help reduce the impact of tansy ragwort, but the ragwort flea beetle is the most effective.

A third (and not approved) insect is the cinnabar moth, Tyria jacobaeae. These insects are not available for distribution in Washington state because of non-target feeding on species other than tansy ragwort. Cinnabar moth is well established in King County, however, moving the insects to new areas is discouraged as the larvae also feed on 2 native species (Senecio triangularis and Packera pseudarea) and one ornamental species (S. bicolor, or dusty miller).

These agents take up to 6 years to have a significant impact. Any biological control is only recommended for very large infestations that cannot be controlled by other methods.

For more information about these biocontrol agents, please visit the Integrated Weed Control Project.

Chemical control

Stay safe when using herbicide: 

• Always read the label before use. 
• Wear a long-sleeved shirt, long pants, shoes, and eye protection. 
• Follow state and local regulations.

Herbicide may be the most efficient method for larger infestations and can be used in combination with other control methods. If in a grassy area such as a pasture, it is best to use broadleaf selective herbicides such as triclopyr, 2,4-D and aminopyralid. They will not damage the grass, which will help prevent tansy ragwort and other weed seeds from germinating. Glyphosate is non-selective but can be used where weeds are very dense or where the chance of damaging grasses is low. Apply in spring before flowers appear or in the fall when new plants come up as rosettes.

Disposal instructions

If livestock or horses are present, you should bag and dispose of all plant parts in the garbage. Do not stock pile flowering plants on a burn pile- they will still set seed.

If livestock or horses are not present, you can bag the flower or seed heads. The remainder of the plant can be pulled or dug up and left to dry out and die.

Tip on bagging plants that have seeds:

• Hold a garbage bag open near the plant.
• Using a spray bottle- mist the seeds of the plant with water.
• Gently bend the plant so that the head is inside of the bag.
• Cut off the seedhead of the plant.
• Then remove the rest of the plant.

Noxious Weed Disposal - Washington State Noxious Weed Control Board

Are your weeds piling up? - Noxious Weeds Blog