Most gardeners consider musk thistle a noxious weed and dig it up and try to eradicate it. Carduus nutans is specifically a plumeless thistle. It has reddish purple spines on a rounded bloom. It belongs to the sunflower family. It comes from South Asia and is an ornamental herb. It grows from seed or propagation. Because these plants have a normal bend of 90 or 120 degrees, they have the name "nodding thistle."
The plant grows all over the US and many parts of the world notably Canada, Australia and New Zealand. It came to the US in the nineteenth century and still grows here. Farmers don't like it. It is poisonous and likes to grow in pastures. Other places it grows are lower elevations mostly at sea level. It likes neutral and acid type soils.
The reason this plant is so bad is that its head or bloom produces thousands of seeds at a time. The seeds fall to the ground and lay dormant until the next spring when they sprout. The wind blows some of the seeds to nearby areas. The seeds can grow for to ten years after lying dormant in the soil. Landslides and floods only make it easier for musk thistle to survive.
The thistle grows up to six feet tall. Animals, wild or domesticated, cannot eat the plant. It has a cottony stem and sharp-edged leaves. The blooms themselves have spikes that make them distasteful to wildlife. The blooms can have a 1 ½ to 3 ½ diameter.
The best way to control this thistle is with herbicides. Gardeners must apply the chemical to the round part of the plant before the plant reproduces in spring or fall. Elimination of the seed will not occur if done at the wrong growth period of the thistle.
A number of chemicals are available but application times differ. Check labels and also rates and application table for musk thistle. Tordon, Milestone, Transline, Banvel/Vanquish/Clarity (dicamba) require higher rates of application as much as two pints. When using Cimarron and Escort, gardeners need to add another non-ionic surfactant with a 0.5 oz rate of application to kill the seeds. Mowing with the herbicide should control the spread and growth of the musk thistle.
Pulling the plants up with gloves hands also works well where the plants have not grown too densely. Persistence is necessary and the bagging and removal of the plants to a landfill is the most effective way of ensuring that the plant will not leave any seeds behind.