How to eradicate Plumeless Thistle?

Asked August 10, 2016, 3:48 PM EDT

We have property in the Timber Creek area of Island Park, adjacent to the 2Lazy2 ranch in Fremont County. We have an invasion of what we are almost certain is Plumeless Thistle - about 50 plants in an area close to the house where we mow the weeds and native plants. Our ID is based on your booklet Idaho's Noxious Weeds. The photos and description exactly match what we see in our yard (tho we haven't seen the flowers & seeds yet). The larger plants have flower stalks but have not yet flowered. Some just have the rosettes.
What do you advise in order to eradicate these plants?
We will be at our property through September, so we could do a fall application of an herbicide. We could also spot-treat.
Thank you!

Fremont County Idaho

3 Responses

Hi there!
Here are our UI guidelines for management of plumeless thistle. For a September application, it would seem that Picloram would be your best bet. The very best time to spray any of these products is in early spring/summer, when the plant is still in the small rosette stage before the flower stalk bolts.
The herbicide Milestone has shown a lot of promise, however, this is a long lasting residual, it can remain active in debris, straw, hay or manures. http://idahoweedawareness.com/netcenter/library/idahoweeds/pdfs_docs/Musk_biennial_thistles_Fact_She...

Plumeless thistle
Carduus acanthoides

Chemical control

Herbicide: Weedar (2, 4-D amine)
Description: Apply 2 to 4 pt/A 2,4-D amine
Timing: Rosette to bolting stages

Herbicide: Banvel, Clarity, Vanquish (dicamba)
Description: Apply 0.5 to 1 lb ae/A dicamba
Timing: Rosette stage

Herbicide: Escort XP (metsulfuron)
Description: Apply 0.5 to 1.0 oz/A Escort XP; use a surfactant
Timing: Rosette to bolting stages

Herbicide: Tordon 22K (picloram)
Description: Apply 8 to 12 oz/A Tordon 22K
Timing: Rosette to bolting stages; in fall prior to freeze up

Herbicide: Milestone (aminopyralid)
Description: Apply 3 to 5 oz/A Milestone
Timing: Rosette to bolting stages in early summer; seedling to
rosette stages in fall

Herbicide: Chaparral (aminopyralid + metsulfuron)
Description: Apply 1 to 2.5 oz/A Chaparral
Timing: Spring to early summer to rosette or bolting stages; fall to
seedlings and rosettes

Herbicide: Forefront R&P (aminopyralid + 2,4-D)
Description: Apply 1.5 to 2 pt/A Forefront R&P
Timing: Rosette to bolting stages in early summer


Thank you Ariel. Meantime we consulted the weed supervisor for Fremont County who recommended Milestone. We see your caution about it being a long-lasting residual so we will be careful with it. The concern would be about an animal ingesting it? No livestock are in the area, but deer could browse. Any additional comments on that?

One of the things a lot of people like about Milestone is that it CAN be used in pastures, if instructions are followed. I honestly don't know about deer, but perhaps Fish and Game would have that answer! I appreciate your concern and caution! I think the product will really help you get control of this weed, though, when used sparingly.