NORMAN — Cleveland County has a beautiful problem. Most do not equate beauty with being problematic, but in the case of the noxious and non-native musk thistle, it is quite common.
This showy but aggressive herb is ransacking our county, with each plant capable of producing more than 120,000 wind-dispersed seeds. Individuals wishing to report thistle infestations that are not being controlled can file a complaint with the Department of Agriculture, Food and Forestry. The landowner will then be notified and informed about their responsibility.
The Oklahoma Noxious Weed Law declares musk thistle a noxious weed and public nuisance. Landowners whose land is infested are required to control thistles on their property. Failure to do so may result in a fine.
Many of our native thistles are small and less obnoxious when compared to musk, scotch or bull thistle. Their foliage is normally silver and their flowers are far less conspicuous. They are not normally over knee high, whereas musk thistle can grow 5 or 6 feet tall and has green leaves.
Native to Asia and Europe, musk thistle is a biennial plant belonging to the Aster family. Some plants may act as annuals and complete their life cycle in one growing season. Under normal circumstances, however, seeds germinate, develop a prostrate growth form called a rosette and wait. The following growing season, musk thistles grow spiny leaves and shoot up a tall set of flower “bolts” for reproduction. Upon dispersing seeds, the plant dies. It reproduces only by seed. Their showy flowers range from a deep rose or violet color to purple or occasionally white.
Musk thistles are easy to kill with herbicides, but timing is critical. The best chemical control of musk thistles in Oklahoma occurs during March with applications to rosette-stage plants. If 2,4-D or Transline (one-third to two-thirds pint/acre) is used, spray before plants start bolting. Once plants bolt in April, they are difficult to control. However, 90 to 100 percent control is possible with Grazon P+D (2 pints/acre) or Weedmaster (2 pints/acre).