For the uninitiated Washingtonians to the world of all things Flora, the mid-July blooms of bright yellow buds can be a pleasant sight as a reminder to enjoy the sunshine while it lasts. However those yellow blooms may cast a more ominous shadow than the storm clouds that frequent the Pacific Northwest.
Of course not all yellow petals are created equally, and these particular ones belong to the, rather infamous, tansy ragwort.
Is it tansy? Count the petals! Tansy Ragwort flowers have 13.
This species is a nonnative, noxious weed. Tansy Ragwort originates in Europe and Asia and was first documented in Oregon in the 1920’s. In a not-so-unfamiliar story, it is thought that this species made its grand voyage to North America in the ballast water of ships.
Tansy ragwort is a Class B noxious weed in the state of Washington. According to the Washington State Noxious Weed Control Board a Class B noxious weed is a nonnative species which has widespread distribution in some parts of the state but limited in others; containment and prevention of new infestations are the primary goals when it comes to this weed class.
Why is Tansy Ragwort considered a noxious weed?
As is the case with many noxious weeds, tansy ragwort’s ability to proliferate makes it a threat to native species. A single plant is able to produce up to 150,000 seeds outcompeting and rapidly displacing native vegetation.
The threat does not end there when it comes to tansy ragwort; this weed also contains toxic alkaloids in every part of the plant which pose a threat to livestock and humans!
Tansy ragwort poses a risk to grazing animals like cattle and horses as they are most likely to graze on the toxic plant in hay or silage. The poison is slow-acting, so eating it will make livestock sick and continued exposure will lead to death of the animal.
Hopefully you don’t go around eating random plants that you haven’t identified, but just in case, this is one to avoid! Human consumption of tansy ragwort will lead to liver failure and is likely fatal.
That being said, direct consumption is not the most common way that humans are exposed to the these toxic alkaloids. Instead, humans are most often exposed to tansy as it contaminates animal products that we consume. Dairy livestock exposed to tansy ragwort pass the toxins up the food chain to us; likewise honey is another commonly consumed product that can carry these alkaloids as well. This contamination can drastically alter the taste of these agricultural products (for the worse) and long-term consumption by humans is a concern.
Tall Tansy Tales?
There is much to say about the toxicity of tansy ragwort, but one thing that it doesn’t need is to be exaggerated. A common theory that you can find on Facebook groups, message boards, or even just by word of mouth is that if you so much as simply touch tansy ragwort those toxins can be absorbed into your skin and harm you.
The burning question… Is this fact or fiction?
The answer is actually lies in the middle. The World Health Organization does recognize that the alkaloids present in tansy ragwort plants can be absorbed through the skin, however further research showed that the amount absorbed is very low (up to 50 times less than when consumed). Not only is the concentration of the alkaloids lower, but researchers identified that in order for the alkaloids to become toxic they have to be processed in the small intestine and transformed into “free alkaloids” that then cause liver damage. So other than a potential allergic skin reaction, touching this plant won’t cause you any harm. But it still isn’t a bad idea to use gloves if you’re ever weeding by hand!
Taming the Tansy
This inevitably leads us to the questions: what in the world are we supposed to do about this noxious weed?!
When we discuss controlling noxious species we’ll break down the control options as follows: manual/mechanical control, cultural control, biological control, and chemical control.
Tansy ragwort is a great example of attempting to implement biological control of a noxious weed. Biological control is most simply defined as controlling a pest by introducing its natural predator or “enemy”. In this example that is the cinnabar moth. The cinnabar moth specializes on consuming tansy ragwort; adults will lay their eggs on the underside of the tansy leaves and when they hatch the caterpillars will feed on the host plant. According to Oregon State University this moth species was first released in the 60’s and is widely considered a biological-control success story. Unfortunately, University of Washington conducted a three-year survey which showed that cinnabar moths are now also consuming native plant species including native wildflowers. Althought the moth is not considered a pest just yet, UW says in their own words that this serves as a “cautionary footnote to the tansy ragwort success story”.
So it turns out that you can’t rely on a benevolent swarm of moths to swoop in and save the day. You might not even feel like the day needs saving as long as you know not to eat it and you don’t have livestock. But the problem is, even if you don’t have livestock, you not only should still take action (to keep those 150,000 seeds from spreading to your neighbors) but Pacific County residents are legally required to remove tansy ragwort identified on their property.
If you can find them in their first year of growth, the rosette stage, this is the best time to pull them up!
If you wait until the second year it gets more complicated, because the seeds are viable as soon as the flowers form. This adds an extra step to your management as you will need to get the flowers into a sealed bag to avoid the seeds spreading.
Have questions or having trouble identifying what plant your looking at? Feel free to contact your Conservation District to get free technical assistance for this or any natural resource issue!
Resources
General Tansy Ragwort Info:
Washington Native Plant Society
Cinnabar Moth:
Ridgefield National Wildlife Refuge
More on Toxicity:
English 
Español de México