Weed of the Month: Bull/Musk Thistle
.png)
This Weed of the Month is a two-for-one deal: we’re covering bull thistle and musk thistle. They have a lot in common, from bright purple flowers to pesky spikes, with a few key differences we’ll highlight. Their most important similarities? They won’t stand a chance against you after you’re done reading.
Fast Facts :
Bull Thistle/Musk Thistle Origins:
Bull thistle and musk thistle (Cirsium vulgare (Savi) Ten. / Carduus nutans L) share the same origin: they came to North America in the mid-1800s from Europe, Asia, and Northern Africa, most likely as an accident. Both spread by seed, which means they spread throughout most of the continent by human movement, animals, and the wind.
Bull Thistle/Musk Thistle: Plant Description
Both plants are biennial forbs in the Asteraceae (daisy) family, and both grow from a taproot to form a basal rosette in their first year. In their second year they grow one to many stems, with bull thistle being 2 to 6 feet tall and musk thistle reaching up to 7. They both have green basal leaves that occur alternately up the stem, decreasing in size, with pointed spines.
Perhaps the best way to tell the difference is the terminal flowers. Both are purple discs, but musk is larger, about 3 inches across, and they nod when mature. On the other hand, bull thistle flowers are 1.5 to 2 inches across, with florets that may be enclosed in spiny bracts that form a bulb at their base. They both flower from early summer to fall.
.png)
Bull Thistle/Musk Thistle Habitat
They came here together, and they spread together. Bull thistle and musk thistle have spread far throughout the US, and both thrive in disturbed or neglected sites, along roadsides, railways, ditch banks, and waste areas. They’re also common in pastures, rangeland, and lawns—which is where they can outcompete more desirable natural plants and reduce the amount of foreable plants for livestock.
Bull Thistle/Musk Thistle Management
Have an infestation of both? Luckily you can take on both with the same methods.
There are currently no biological control agents available, but controlled grazing of bolting and flowering plants can help keep them under control. Mowing can help prevent seed production, but once they’re present hold off. Their taproot is another achilles heel, since it can be easily handled by pulling it out or severing it below ground.
Herbicides are effective in case of a larger infestation. Spring and fall treatments are ideal, but treatment on bolting plants can work too. Always read the label before using any herbicide, and contact us if you have any questions.
For a problem infestation, herbicide treatments are effective, ideally with spring and fall treatments of rosettes. For flowering plants, chop them and treat what’s left to prevent reflowering. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.