Bull Thistle (Cirsium vulgare)
Biological Control Program

 Bull Thistle Flower

 

Bull thistle (Cirsium vulgare), a Kansas county option noxious weed and native to Eurasia, is usually a biannual.  In the late spring bull thistle bolts and forms flowers from July to September that are dark purple to pinkish purple.

Bull Thistle Flower Buds

 

Two insects, musk thistle head weevil, Rhinocyllus conicus, and musk thistle rosette weevil, Trichosirocalus horridus, are approved for biological control in the Kansas Department of Agriculture bull thistle control program.  Frequently, the head or rosette weevils use the bull thistle as an alternate host.  For more information on the weevils, refer to the KSU extension bulletin "Biological Control of Musk Thistle in Kansas".