Musk thistle was first introduced in America in 1850, most likely as an ornamental plant due to its large showy purple flowers. The plant was discovered in Washington County, Kansas in 1932. It was declared a noxious weed in 1963. Today Musk thistle infests over 700,000 acres statewide. Musk thistle is a tap rooted biennial, and sometimes a winter annual plant, that spreads by airborne seeds. Seedlings germinate in fall or spring, producing a flat, low growing rosette that can reach 3 feet in diameter.
Flowering normally occurs during the second year. Two inch flowers are purple, or rarely white. Seeds are connected to a feathery pappus, or “parachute”. While the pappus may drift long distances, most seeds break off and are deposited within 100 feet of the plant. Seeds remain viable 20 years or more. A single plant can produce over 100,000 seeds.
How to Control Musk Thistle
Preventing seed production is the key to controlling Musk thistle. Mowing Musk thistle plants over a two year period to prevent flower production will control the weed. Hand pulling or digging plants so that two inches of the tap root are removed will also eradicate Musk thistle. Pulling or cutting flowers or seed heads with proper disposal in a landfill will suppress Musk thistle infestations.