Musk thistle is a large perennial weed with 6-foot stems and spiny leaves. And its large, purple blossoms are deceptively attractive. Musk thistle is a particularly aggressive weed. It commonly crops up in yards or pastures that receive ample amounts of sunlight and moisture. And if allowed to spread, it will rob more desirable plants of vital nutrients. To get rid of musk thistle, you must treat it with a combination of control methods.
Physically remove musk thistle from organic lawns. Use a sharp, flat shovel to remove the plant just below the soil to separate it from its root system. Collect the removed plants and burn them to destroy the seed.
Apply pesticides to musk thistle. Use a commercial herbicide prescribed for use on musk thistle like Tordon 22K (picloram) or Vanquish (dicamba). Spray the musk thistle between spring and fall, before it produces seeds. Follow the manufacturer's instructions for mixing and application rates.
Purchase and release musk thistle seed head weevils (rhinocyllus conicus) into the area. Adult weevils will deposit their eggs on the musk thistles flowers. When they hatch, they will eat the developing seed and reduce seed production by roughly 50 percent. Seed head weevils are ideal for use on organic plots, in conjunction with physical removal..
Properly maintain the grass or ground cover. Regularly fertilize it, reseed any thin spots, provide it with adequate amounts of water and prevent over-grazing. Musk thistle cannot compete successfully against healthy, vigorously growing ground cover.