View All Posts

Aug 04

Wednesday Weed Update

Posted on August 4, 2021 at 7:26 AM by Alicia Doran

Musk Thistle Removal

Many folks are working hard these last couple weeks removing their Musk thistle.  While this is admirable and absolutely necessary, it is also a task that could be a lot easier.

The best time to remove Musk thistle is at the rosette (seedling) to early bolt (12 inch tall) stage before flower buds form.  It is best to get the top couple inches of the root so the plant won't grow back.  In our area fall rosettes usually start showing up in September.  If not removed, they will overwinter and then start growing again next spring.

In the spring, overwintering rosettes and new rosettes start to grow and get active as things warm up, usually around May.

In looking at the Musk thistle this year, it appears that there is a good crop of seedhead weevils.  This biological control agent can help reduce the amount of seed.  The larval form feeds on the seedbed inside the flowers.  If you are seeing tan-colored flowers in amongst your large purple heads, break a couple open to see if the seeds are being eaten.  If so, leave the tan flowers so the weevils can complete their cycle.

Need more info?  Musk Thistle page

Musk thistle flowers.  Musk thistle seedhead weevil larva.