***IMPORTANT NOTE***

According to Idaho Code 22-2407, Idaho property owners carry the primary burden of controlling noxious weeds on their land.  County Weed Superintendents may only treat noxious weeds on private property if the landowner fails to fully mitigate the situation.  In such instances, the County will treat the noxious weeds and bill the property owner for the weed control efforts. 

Control Canada Thistle

New Herbicides Tame Canada Thistle!

Always read the label, and follow the directions on all herbicides you are using. Be sure you completely understand the instructions for use of a product in your specific application. Get a recommendation from a licensed consultant, before using products you are not familiar with.

Canada thistle is a noxious weed commonly referred to as a “creeping perennial” and uses its extensive root system to reproduce itself and spread to new areas. Canada thistle outgrows desired plants by forming dense colonies and taking valuable nutrients and moisture away from the desirable vegetation. Canada thistle, with its, long stems, fast growth, and roots that have been found as deep as 27 feet below the surface, can be very difficult to control with mechanical cutting, hoeing, or through field tillage. Fortunately, some excellent herbicides have been registered for use against this noxious weed.

Chlopyralid, the active ingredient found in some specialty herbicides, is extremely effective on Canada thistle. Consult with a crop protection specialist to find the product that fits your specific situation. Different products are labeled for different sites, and might not be appropriate for the intended use of your property. Glyphosate, the active ingredient in Round-Up®, can also be effective, but should only be used where no desirable plants are growing, since it kills both broadleaves and grasses.

There is a group of herbicides called Sulfonyl-Ureas, that are sometimes mixed with 2,4-D, and/or related herbicides, that provide excellent control of Canada thistle. Using two or more herbicides together, with two or more modes of action, often increases herbicide effectiveness, and  can avoid herbicide resistant weeds. These combinations can usually be used in pastures or other situations where desirable grasses or grass crops are growing. Again, consulting with a licensed crop consultant is important when creating a weed control plan for your property.
Several products marketed by home and garden stores contain these herbicides, and are packaged and labeled for use by the general public.

Effective control of Canada thistle requires that you know when to apply herbicides. Some products should be applied while the plants are still small, where others should be applied when Canada thistles are in the “bud” stage, or fully mature. Carefully reading the herbicide label will help you get the most out of your weed control efforts.
A common problem affecting Canada thistle control comes from applying too much herbicide on the targeted plant. Spot spraying a systemic herbicide until it is running off the leaves of the plant, will quite often kill the above-ground vegetation of the plant, yet not allow time for the herbicide to be translocated to the root system. This leaves the root system alive, and the Canada thistle will grow back the next season.

Always read and follow the directions on the label of the products you are using. The manufactures of today’s herbicides spend vast sums of money to study and test the products they sell, by using the products as they were intended, you can rid yourself of this, and other noxious weeds.

If we can help you with a weed control problem, or provide clarification about using herbicides, feel free to call us at Ada County Noxious Weed Control. Our phone number is (208) 577-4646, or visit us at our office at 975 E. Pine, Meridian ID, 83642, 7:30 a.m. - 5:00 p.m.

All photos this page: University of Wyoming, Ext. Service, Weeds of the West.