Tansy Ragwort (Senecio jacobaea) on Jul 31, 2024
Submitter does not have a specimen
EDRR Status: Local expert notified
Description of specimen
Walking the trails at Witham Hill Nature area, the patches of TR are easy to see.
Also found some on Witham Hill Drive at Fernwood Circle (5 plants). Owner will remove.
Typically we depend on insects to help us manage tansy ragwort. In Oregon there are at least 3 insect pests that eat different parts of the plant and they’re highly effective at diminishing populations. These insects, which we refer to as biocontrols, were intentionally released in Oregon after thorough testing to make sure they didn’t damage important agricultural crops or native vegetation. Every few years, we find that the insects have done so well in reducing the prevalence of their host plant, that they themselves crash in population. Once this happens, the host plant then rebounds and that’s likely one reason we have so much tansy in Benton County right now. Also it seems that we’ve had optimal weather conditions for tansy ragwort locally.
At Benton SWCD, our resources to treat weeds ourselves is very limited so we focus our efforts on educating the public about noxious weeds and how to control them. Our recommendations on tansy are to control it aggressively if you have livestock or if you sell hay or other livestock forage from your farm. Tansy is toxic to livestock. If you have tansy in bloom right now near a livestock operation, we’d encourage you to go ahead and cut it or pull it so that it doesn’t go to seed. It’s too late in the season to wait for the biocontrol to move in to prevent it from seeding.
Unfortunately, with limited time, we all have to prioritize. In areas away from livestock, controlling tansy is a bit less of a priority so don’t be surprised if you see some land managers focusing their efforts on other things. While it’s always good to remove noxious weeds, populations of tansy will likely be controlled by biocontrol insects in the next year or two.
For more information on biocontrol, take a look at this brochure: https://www.oregon.gov/oda/shared/Documents/Publications/Weeds/BiocontrolBrochure.pdf
Michael Ahr
Aug. 4, 2024, 11:12 p.m.