Weed Killer for Thistles

Written by cate kulak
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Weed Killer for Thistles
Thorny thistles can be difficult to eradicate without weed killer. (thistle image by Henryk Olszewski from Fotolia.com)

Weedy thistles are difficult to eradicate. Thistles are perennial or biennial. Effective control of each class is slightly different, based on their different methods of reproduction.

Timing For Biennial Thistle Herbicide

Apply herbicide for biennial thistles during their rosette stage of growth to prevent seeding. Biennial thistles include musk thistle (Carduus nutans), plumeless thistle (Carduus acanthoides) and bull thistle (Cirsium vulgare).

Weed Killers for Biennial Thistle

The University of Kansas weed control program recommends different chemical herbicides for spring and fall application for biennial thistles; however, they identify Picloram and Aminopyralid for use in either season.

Weed Killers for PerennialThistle

In a study at Iowa State University, the best weed killer for the perennial Canada thistle (Cirsium arvense) was picloram, though Stinger worked comparably well. However, they did not test other perennial thistles that are less invasive, such as Flodman thistle (C. flodmanii) and wavyleaf thistle (C. undulatum).

Warning for Perennial Thistles

Perennial thistles have extensive root systems, which are not obvious from above ground. Therefore, you may need multiple herbicide treatments.

Timing for Perennial Thistles

The University of Minnesota recommends applying herbicides to perennial thistles just after budding, but herbicides applied soon after seed dispersal are almost as effective.

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