The Strategy - Tansy ragwort (Senecio jacobaea) is an exotic invader from Europe that is often contaminated in hay. DO NOT mix this up with the weed on our ditch banks called Common Tansy (Tanacetum vulgare L.). Many people will call and state that they have this noxious weed when in fact they have Common Tansy. Tansy ragwort grows to a short of height of about 3 foot tall, as where Common tansy grows up to 7 feet tall. They both have yellow flowers but Tansy ragwort’s flowers have conspicuous petals with an orange center, where Common tansy’s flowers are in clusters on top of the stem. Tansy ragwort is a biennial that germinates in fall or early winter. So far, we have only seen this plant in Northern Idaho.
The Attack - This plant can produce over 150,000 seeds per plant which can remain dormant in the soil for up to 15 years. The plants fibrous system of coarse, light-colored roots spreading form the crown can produce small adventitious roots that are stimulated by pulling or mechanical destruction if the majority of the root is not removed. This plant is extremely toxic livestock, especially horses, which becomes a problem if it is
baled in hay. The toxic alkaloids are also found in honey that is produced from this plants flower.
The Defense - Mechanical control can be effective on new infestations. Once the plant is established it can be controlled by cutting, but it has to be performed twice a month throughout the growing season. There are a few biological control insects that are effective at removing the vegetative growth. Numerous herbicides are available to control this invader. Banvel, Tordon 22k, Milestone, and Curtail are just few. Treat the weeds prior to flowering. Keep the livestock off the treated field for a couple of weeks after treatment as the treated plants odor will be altered after application thus the animals may believe them to be foragable. Please contact your local county weed superintendent if you believe you have this plant but don’t mistake it for Common tansy.
PLEASE NOTE -The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.
For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.
U of I Idaho's Noxious Weeds Control Guidelines (183 KB PDF download)