Canadian Thistle - Ask Extension
We have a big invasion of Canadian thistle. We have cut it back, used roundup, or used the vinegar/dawn approach and it will come back bigger and stro...
Knowledgebase
Canadian Thistle #877710
Asked July 17, 2024, 8:22 PM EDT
We have a big invasion of Canadian thistle. We have cut it back, used roundup, or used the vinegar/dawn approach and it will come back bigger and stronger. We hate to use anything more powerful since it is a a grove of vary tall and healthy cryptomeria evergreens.
Do you have any suggestions?
Howard County Maryland
Expert Response
It should not require anything stronger than glyphosate, the ingredient in many, though not all, formulations of Roundup and other brands of systemic herbicide. However, repeat applications of glyphosate may be needed for any tenacious, well-established perennial weed like Canada Thistle.
The ideal time to apply a systemic in this case is just before (or just after) bloom, which is probably about now (or the next few weeks). The plant has directed some of its root energy stores into blooming or developing seed, so is in a position for a root-killing herbicide to cause more damage, thus killing the plant more effectively.
Vinegar is not an herbicide except when labeled for that use as a much stronger concentration of acetic acid. (Caustic enough to be hazardous when used without sufficient skin and eye protection.) Household vinegar is much too weak to kill any perennial weeds, nor will it move into roots, so will only temporarily injure surface foliage at best. Household detergents and soaps should also not be used with any pesticide or home remedy unless specifically instructed in the directions of an EPA-registered product. Penn State Extension has a good article about why home remedies are not recommended.
Miri
The ideal time to apply a systemic in this case is just before (or just after) bloom, which is probably about now (or the next few weeks). The plant has directed some of its root energy stores into blooming or developing seed, so is in a position for a root-killing herbicide to cause more damage, thus killing the plant more effectively.
Vinegar is not an herbicide except when labeled for that use as a much stronger concentration of acetic acid. (Caustic enough to be hazardous when used without sufficient skin and eye protection.) Household vinegar is much too weak to kill any perennial weeds, nor will it move into roots, so will only temporarily injure surface foliage at best. Household detergents and soaps should also not be used with any pesticide or home remedy unless specifically instructed in the directions of an EPA-registered product. Penn State Extension has a good article about why home remedies are not recommended.
Miri
