Plumeless thistle is a winter annual or biennial and generally found in eastern North Dakota. It can become very weedy and form dense colonies in pastures, rangelands, along waterways, ditches and roadsides in summers following wet falls. Many pastures in Cass County have infestations of Plumeless thistle. The numerous spiny branches make walking through infestations by people or animals very difficult.
Plumeless thistle usually grows about 4 feet tall; however, patches have been seen growing 6 to 8 feet tall. The stems are winged and very branched, giving the plant a candelabrum appearance. The wings are very spiny and are continuous along the stem. The leaves are deeply lobed, and very pubescent underneath. Each leaf lobe has one to three very sharp spines. The flowers heads are small (.5 to 1.0 inch) and very numerous. Flower color ranges from pink to purple to very white. The plant bolts in the early spring and flowers late June through July.
Control on non-crop lands:
Chemical: Fall is the preferred time for applying herbicides to biennial thistles. Seedlings that emerge in the summer are in the rosette stage and are most susceptible to herbicides. Milestone (aminopyralid), Curtail (clopyralid), Tordon (picloram), dicamba (various) or Overdrive (dicamba plus diflufenzopyr) are very effective for fall treatments. Spring treatments can be accomplished with products that contain methsulfuron (Escort, Cimarron Max, others) which will eliminate seed production when applied in the bolting to bud growth stages.
Cultural: Repeated mowing will reduce plumeless thistle populations but must be done prior to flowering or viable seed seed be produced.
Biological: Both Rhinocyllus conicus and Trichosirocalus horridus, which were released for musk thistle control, attack plumeless thistle.