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Canada Thistle Control Straregies Sources: "*Czarapata,Elizabeth J."Invasive Plants of the Upper Midwest:an illustrated guide to their identification and control" University of Wisconsin Press,2005 **Invasive Plant Species page:Canada Thistle.Wisconsin Department of Natural Resources website.Accessed 2/10/08 http://dnr.wi.gov/invasives/fact/canada_thistle.htm updated 10/3/04 **Minnesota invasive non-native terrestrial plants:an identification guide for resource managers.Published by MNDNR 2002,Trails and Waterways Division ***Habitat Forever,LLC(2008)"Canada Thistle Control"Internal document outlining approach to thistle control. ***Natural Resources Conservation Service(NRCS)(2007)."Pest Management-Invasive Plant Control:Canada Thistle (Cirsium arvense)"Conservation practice job sheet MN-797 Canada thistle(Cirsium arvense)thrives in sunny,disturbed sites.It can invade upland habitats such as prairies and savannas as well as wetland habitats such as sedge meadows and wet prairies.Seed of this thistle are dispersed by wind and can remain viable in the soil up to�0 years.Once established,the plants spread rapidly by rhizomes or root segments.Mechanical and chemical control strategies are often used in combination for Canada thistle control. Con- ducting late spring burns is beneficial during the first three years of the control effort.Canada thistle can be treated with Transline,Stinger or Milestone herbicide in mid-June prior to flowering. Canada thistle is a perennial,while plumeless and bull thistles are biennials.The biennial thistles can also be treated with Transline,Stinger or Milestone or they can be cut or clipped.These biennials normally produce only rosettes (no flowering)the first year and then flower the second year.Clipping the buds off just as flowers begin to open the second year should prevent them from going to seed.Over time biennials will be out-competed by upland grassland species.Unless patches are very large,it is recommended that herbicide be applied selectively with back-pack spray- ers,becauseTransline and Stinger affect composites and legumes,both of which are components of upland prairie and woodland edge plantings. Mechanical Control-Hand pulling or cutting only work well if done frequently during the summer months.It is best if cutting/pulling occurs at least three times in the summer;once in June,once in August,and again in September. Due to persistence of seed bank in heavily populated areas,pulling or cutting alone may not be entirely effective. Chemical measures or burning may be required during subsequent springs,depending on quality of habitat and nature of site.Another alternative,in sites that are larger and fairly disturbed,is to mow as close to the ground as pos- sible while the plant is in full bloom(June through late August).Mowing should be done at least once a year and will have to be repeated for several years thereafter.Some evidence has shown that mowing alone may be effective in the northern part of the state but mowing and chemical treatment is generally needed further south. Chemical Control-Chemical controls are not recommended in high quality habitats as damage to native plants can be worse than damage to thistle.If absolutely necessary,chemical control methods are effective only if done at the proper time.Chlopyralid or Aminopyralid herbicides are typically used for Canada thistle control. In high quality habitats that have a substantial infestation,careful wick or spot spray application of a Clopyralid formulation is recom- mended. Chemical control is often conducted in restored sites in combination with mowing.See the discussion of "Combination Methods"below for specific recommendations. Prescribed Burns-Fire is best when used in late spring(early May to early June).If the burn is done too early it may actually promote growth of Canada thistle and other invasives.Burns should be once a year for at least three years to see significant reductions in dense populations. The impact on other species should be assessed for spring burns that will be conducted during subsequent years. Combi�ation of Methods-Whenever possible,spot treatment of thistle is recommended to minimize impact on native forbs.In situations where thistle covers large areas or stands are comprised of native grasses,a combination of mowing and herbicide application can be used.Mowing is conducted in early June when thistle is in the bud stage. Mowing at this time of year will reduce the plants energy reserves.Herbicide treatment is conducted in the fall after the second hard frost,commonly with Aminopyralid(Milestone)herbicide at a rate of S-7 oz.per acre.Waiting until �E1 SECTION S VEGETATION ESTABLISHMENT