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Canada Thistle In Colorado Newly Invading weed species get a lot of atten- tion, but for sheer staying power and pure cus- sedness it's hard to beat Canada thistle. This weed has been around a long time and continues to plague Colorado farmers, ranchers, and landowners. Canada thistle Is especially troublesome because of Its persistence In cropland as well as range and pasture. Research has Shown yield reductions Of 35°~G In Montana wheat fields where there were 12 Can- ada thistle shoots per square yard and yield losses of 60% where There were 25 shoots per square yard. This weed reduces production of pasture and range In two ways: It Curtails grass production through competition for soil moisture and sunlight, and Its sharp spines deter livestock from grazing In areas of Infestation. Canada thistle is a member of the sunflower family. Leaves are oblong to lance-shaped and may be Irregular and deeply cut with spiny margins. Flower heads are smolt, Compact, and vary from Ilght lav- ender to purple In color. This weed Is a perennial with an extensive root system and propagates readily from seed and from root segments. Single plants have been knowri to spread 10 to 12 feet through the soil by root growth In a single season. Because the plant sends up shoots and spreads from underground roots, tt Is generally found growing In patches. New shoots arising from the root system In the spring can become fully developed plants, wtth flowers, In seven to eight weeks. Thus, by root propagation alone, a newly established plant may spread over an area 20 feet In diameter In one year. Canada thistle Can send up new shoots from a depth of several feet, and roots that are unable to grow new shoots Can Still survive underground for up to fNe years. Wlthln three weeks after germination, a new seedling has become a perennial plant and Is capable of regenerating new plants from root seg- ments. Flowers may produce 40 to 80 seeds per head. The fluffy plumes of the seed head can travel long dis- tances on the wind, and this Is the maJor means of spread for the weed. Once Canada thistle Is estab- Ilshed. root propagation allows spread Into surround- ing soil, Increasing the size Of th6 Infestation. Because of the plant's extensive root system and lis ability to regenerate from root segments, herbicides Offer the best means for Controlling Canada thistle. Herbicides must have good iranslocation f0 the roots to achieve effective control. Recommended herbicides for control of Canada thistle In pastures and rangelands Include TORDON' 22K herbicide, BANVEL herbfclde, and 2.4-D. UnNerstty research has shown the best time for controlling Can- ada thistle in pasture or range is when Tne plants are actively growing in the spring or summer at the early bloom stage of growth. Fall is also a good time to spray thistle. These sprays should be applied offer fall rains have caused the plants to resume active growth. All herbicides must be used according t0 label directions. Ranchers or other landowners concerned about Canada thistle Identification or recommended control measures are encouraged to contact the county extension office or weed district personnel for assistance. • •tatl~mart of 7M Oow CMrtueal ComoaN.