Weed-opedia: Musk Thistle
Musk Thistle (Carduus nutans)
What does it look like?: A typically biennial plant with long spiky leaves in a rosette at the base, and a large purple flower atop a spiky stem.
What causes it?: Sparse turf
When does it show up?: Late spring
Best treatment plan: Hand-pulling is effective for small infestations. Post-emergent herbicide applied to rosettes before the flowers arrive, in spring and fall (late enough to kill all rosettes that germinate before winter) are effective for larger infestations. Call a professional for a free quote.
How long will it take to get rid of it?: You’ll need a couple of years to be sure, because it is a biennial plant.