Fall optimal time for thistle control

WYO-BRASKA – Fall is here and now is the time to work on thistle control. Certain types of thistle are designated as noxious weeds both in Nebraska and Wyoming.

“Some of the thistles species are what’s called a noxious weed species which means you can be fined if you don’t take action to control them and that is a statute that varies from state to state,” said Dr. Nevin Lawrence, Integrated Weed Management Specialist at the Panhandle Research and Extension Center in Scottsbluff.

In Nebraska, the thistle species labeled as noxious are Canada Thistle, Musk Thistle, and Plumeless Thistle. Scotts Bluff County also adds Scotch Thistle to the list.

Canada Thistle, Musk Thistle, Perennial Sowthistle, Plumeless Thistle, Scotch Thistle, and Yellow Starthistle are on Wyoming’s list.

Bob Baumgartner, Goshen County Weed and Pest Supervisor, said, “They’re noxious mainly because of spread, being hard to control. Of course, they can be spread by wind, water, wildlife, you name it. Once they take hold, it’s hard to get them under control. They can cause economical harm and damage to everyone involved.”

Thistle can spread very rapidly. The best time for control measures is in the fall and spring.

Jeff Schledewitz, Scotts Bluff County Weed Superintendent, said, “If you can spray them when the rosettes are coming back in in the fall, you can spray that thistle then, that plant is starting to gain energy to winter over. That’s when you’re going to get your best control.”

An article written by Gary Stone, Panhandle Research and Extension Center, states, “Spring or fall applications, especially in the rosette stage, prior to bolting are best. Fall treatments are better after a light freeze and are preferred because they will have less effect on the biological control insects.”

There are several options for controlling thistle.

“It really depends on where the weed is growing and resources the person trying to control it has available to them,” said Lawrence.

“There are three insects that are considered biological control methods at this time. These are the musk thistle head weevil (Rhinocyllus conicus), musk thistle rosette weevil (Trichosirocalus horridus) and the musk thistle tortoise beetle (Cassida rubiginosa).  There is also one pathogen, a rust fungus (Puccinia carduorum),” as expressed by the Stone article. “Products containing aminopyralid, clopyralid, chlorsulfuron, dicamba, metsulfuron, picloram (Restricted Use), triclopyr, glyphosate (non-selective) and 2,4-D have been shown to work.”

Before application of control agents, make sure the chemicals are label for use in your location. 

Other less invasive options include mowing and using a shovel to cut the plant at the root. The best time to use this method is when the heads of the flowers are in the late flowering stage.

For more information, contact your local Weed and Pest Management District Office.


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