Tansy Ragwort

Asked August 28, 2020, 6:48 PM EDT

I remember years ago in the Willamette Valley some sort of insect/worm was brought in to help control tansy weeds. The effort seemed very successful, and I don't recall seeing tansy until the past couple of years. This year it's terrible - I've seen entire pastures completely infested with this weed, and now going to seed. I understand that ingesting the plant is toxic to many animals. Why does there not seem to be any concern with the current infestation of this dangerous weed? Are there any plans to bring it under control again. It seems a shame that the work of prior years is now for naught....

Lane County Oregon

1 Response

Thank you for reaching out to OSU Extension Service with your concerns. The population of tansy ragwort has been on the incline and is very noticeable in the late summer, especially in areas where it isn't being managed. We have been responding to many landowner requests for information about how to manage this toxic weed and provide resources on our website, social media, newsletters and other methods to help keep the word out about this weed. If you have ideas for other ways to share the importance of controlling this invasive species, please let me know!

The biological control you mentioned, cinnabar moth larvae are still out defoliating plants, along with the ragwort seed fly and ragwort flea beetle. We are currently in a situation and have been for the last few years where the biological controls are rebuilding populations. For a few decades their food source was minimal and now there is plenty. We also need more land managers to be aware of the need to manage tansy ragwort via other methods as well to reduce populations.

The following link goes to a resource that can be shared electronically, detailing the trouble with tansy ragwort, biological control at work and other management strategies. https://extension.oregonstate.edu/pests-weeds-diseases/weeds/tansy-ragwort