Seed dispersal and human activities associated with crop production are the main methods of establishment in new areas. Canada thistle produces an abundance of seed carried by the wind with the aid of down. Some may remain in the seed heads and is distributed throughout the winter. Management techniques include hand-cutting, mowing, controlled burning, and herbicides. Due to its perennial nature, entire plants must be killed in order to prevent regrowth from rootstock.
Research is underway into biological control of the weed.
Wet weather was cited as the cause for the emergency condition and resulted in late flushes of Canada thistle and perennial sowthistle in addition to infestations of kochia. Since, flax may be harvested at least two weeks ahead of schedule, Roundup Ultra and Roundup Ultra RT must be applied immediately to allow a sufficient pre-harvest interval. Applicators must follow all instructions, precautions and warnings on the product label, and have a copy of the crisis exemption label in their possession during application. The exemption expires Oct. 1, 2000. EPA several weeks ago, but EPA had not yet acted on the matter.