Musk thistle is a non-native noxious weed that originated in Eurasia. It often grows in pastures, rangeland, open woodlands, roadsides, and disturbed areas.
Musk thistle grows from 2-8 feet tall, and has a fleshy taproot. Because this plant reproduces only by seed, musk thistle is easier to control than the perennial thistles in Nebraska. The large rose-purple flower blooms from late May to August, and is distinctive because of the “crown of thorns” that surrounds the flower. Another distinctive feature of musk thistle is the top part of the stem, with no leaves present for several inches just below the bloom.
Musk thistle is a biennial, which means it takes two seasons to complete its’ life cycle. The first season is a rosette or circle of leaves on the ground. The second season the musk thistle plant will bolt, bloom and produce seed. If allowed to grow to maturity, a single musk thistle plant can produce as many as 20,000 seeds (with as much as 30% being viable). And since this plant only reproduces by seed, the best control is to prevent the plants from blooming and producing seed.
For a small patch, or a few scattered musk thistle plants, digging is one method of control. One word of caution when digging or chopping musk thistle plants; if flowers are present and the chopped thistle is left lying on the ground, the plant may have enough stored energy to go ahead and produce viable seed. Therefore, if you dig or chop plants at a late stage, you should bag or destroy the seed heads. Also, if you cut off the blooms at the top of the plants, musk thistle will work hard to produce viable seed producing flowers lower on the plant.
The EC-130 Guide for Weed Management in Nebraska has several options for herbicide control of musk thistle. During the rosette stage (either fall or spring) musk thistle is most susceptible to chemical control. Always read and follow the label on the herbicide as the label is the law. There are no insects (biological control) approved for release on musk thistle in Nebraska.