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water, or attached to an+.,,a+c, clothing, Caren equip- ment and other vehicles, and to contaminated crop seed. Also, wind may help disseminate seed, but most often, the feathery pappus breaks off leaving the seed attached to the parent plan[ to be disseml- naled by other means. Seed can remain viable In soli up to 20 years and deep burial promotes survival longevity. Canada thistle allocates most otlts reproductive energy into vegetative propagation. New shoots and roots can form mast aztywhere along the root system oC established plants. Tillage breaks up roots and stimulates new plants to develop. Shoots emerge from root and shoot pieces about 15 days after disturbance by tillage. Small root pieces, 0.251nch long by 0.125 inch to diameter, have enough stored energy [o develop new plants. Also, these small roots can survive at least 100 days without nutrient replenlshmenl Crom photosynthesis. Management Lire all weals, Canada thistle Ls managed best through an integrated system that cornblrtes cultural, mechanical, chemfral, and whenever possible. biological control Cultural and chemical methods can be inte- grated In most arvkerttnerrts where Canada thistle 1s a problem MecFtanlcal methods can be easily combined with cultural and chemical techniques to most croPP~g situations lnc~uding pastures and hay meadows. The key principle to Canada thistle crontrol or any creeping perennial Ls to stress the plant. This forces It to use stored root nutrients, which exhausts the supply and even[ualty causes plant death. Canada thistle has the capacity to recover from moat arty stress, including control attempts, because of root nutrient stores. Therefore, returning Infested lazed to a productive state occurs only over t1me. It is essen- tial to develop a sound management plan to Imple- ment over several years to realize success. Cultural control. Grasses and alfalfa can effec- tively compete with Canada thistle tf desirable plant growth 1s favored by good management. Maintain ferillity and, tC possible. motstrue at optimum levels to favor grass or alfalfa growth. Sofl analysts can easily deterrrune fertility needs. These are essential management steps to assure optimum desirable plant growth and competition However, competition alone seldom Is effective against Canada thistle. Chemical control. There are several good herbi- cides registered for Canada thistle control that tray be used m pasture, rangeland and nontsop areas. Before using any herbicide, be sure to read the label thoroughly and follow all directions and use precau- tions. Research at Colorado State University shows that picloram ('1'ordon 2210, dlcamba (BanveA. 2,4-D, and chlorsulturon Cl'elar) are effective against Canada thistle. However, the effeclNeness oC these herblGdes is best when combined with cultural and or m~ha~+- cal control. Banvel and 2,4-D may be used 1n pas- tures. rangeland, and non-crop: Tordon may be applied m permanent grass pastures. rangeland. and non-crop; Telar may be applied In non~snp Drily. Colorado State University data Indicates that Barrel or Telar are effective when combl[ied with 2,4-D as a split-season application. Apply 2,4-D (2.0 pounds al/ A) !n spring when Canada thistle [s 10 inches to 15 inches tall, pre-bud to early bud growth stages; then re-treat in fall with Banvel (2.0 pounds ai/A) or Telar (0.75 ounces at/A) to re-growth. Use a surfactant (0.25 percent to 0.5 percent v/v) with Telar for adequate rnntrol. Barrel also may be applied !n early spring at 2.0 pounds ai/A when Canada thLstle Ls !n the rosette stage. Tordon (0.5 pound to 1.0 pound ai/ A) is effective whenever Canada th1sUe Is actively growing. However. fall appllcatbns ate especially effective. Mechanical control. Mowing hay meadows can be effective tools ffcombined with herbicide treat- ments. Mowing alone 1s not effective unless con- ducted at two-week intervals over several growing seasons. Always combine mowing with cultural and chemical control. Mowing at hay cutting stimulates new Canada thJSlle shoots to develop from its root system. Tn grass hay meadows, fall herbicide ttrat- mentsthat follow mowing can be an effective man- agement system because more Canada thistle foliage is present after cutting to intercept herbicide. Add1- tionally, root nutrient stores decrease after mowing because the plant draws on them to develop new shoots. If a Canada thistle infestation erdsts In a field to be rotated to alfalfa, ft 1s best to control the weed before seeding affalfa. Alfalfa is an effective competi- tor only after H is established and will not adequately establish to awell-developed Canada thistle infesta- tion. ACanada thistle management system can be initiated with crop or grass competition combined with herbkYdes with the plan to rotate to alfalfa at the plan's end. Blolo~cal control Ceutnrhyruus Uturn >s a weevil currently used as a biocontrol agent to Colorado. The female lays eggs underneath the Canada thistle leaves 1n early spring. larvae bore into the main leaf vein then down Into the plant's crown area. u the population is high enough. Plant death can occur, otherwise Canada th1sUe 1s stressed and less vigor- ous. Ceutorhyncus alone wID not effectively control Canada thistle. Therefore, it must be combined with other methods to be successful. AL present, the weevil should be combined with cultural techniques that allow for maximum desirable plant competition with Canada thistle. Research to rnmbine Ceufnrityrtcus with herbiGdes or mowing has not been conducted Reseazr2l has shown that btologtca] and chemtcal mntrol are compatible for musk thistle and most likely will occur for Canada UUsUe. Ceutorhyrrus ULon !s avallable mmmerr~ally and soon wID be available through the Colorado Depart- ment oCAgrlculture. Re-distribution will occur as the insect becomes available.