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' • MUSK THISTLE • <br /> Carduus nutans <br /> K. George Beck <br /> Extension Weed Specialist <br /> Musk thistle is a biennial weed that reproduces only from <br /> seed . Thus, the key to successfully managing musk thistle is to <br /> prevent seed production. It is a weed of pastures, rangeland, <br /> roadsides, waste places and other non-crop areas. <br /> Musk thistle can germinate and emerge in spring or fall . <br /> Germination and seedling establishment is positively correlated <br /> with moisture and light implying that damaged pasture or , <br /> rangeland is prime area for musk thistle invasion. However, musk <br /> thistle can establish in good pasture or rangeland. <br /> Musk thistle emerges in early spring (or fall ) and develops <br /> into a rosette . It overwinters as a rosette and resumes growth <br /> the following spring when conditions are favorable. Most plants <br /> bolt in May and June , then flower, set seed and die (it generally <br /> flowers and produces seed within 45-55 days after bolting <br /> begins) . Thus , musk thistle lives for two years but spends about <br /> 90% of its life cycle in a vegetative condition.. <br /> Musk thistle is a prolific seed producer and can set 10,000 <br /> to 11 , 000 seeds per plant. However, only about one-third of the <br /> seed produced is viable. Taller plants growing somewhat isolated <br /> can have more than 100 heads . Musk thistle is indeterminate and <br /> plants bloom over 7 to 9 weeks . Seeds mature and begin to <br /> disseminate about 2 weeks after bloom. Thus , a plant can be <br /> setting seed from the terminal inflorescence while lateral <br /> flowers are developing . Most of the seed falls .in the vicinity <br /> of the parent plant. Less than I to 3% of the seed is, <br /> disseminated 100 meters or more from the :parent plant '. <br /> Musk thistle is not difficult to control . Preventing seed <br /> production is the key to its management. Tordon 22K (picloram at <br /> 0. 125-0 . 25 lb ai/A) ) , Banvel (dicamba at 01. 5-2 . 0 lb ai/A) ) , <br /> 2, 4-D (at 1 . 5-2 .0 lb ai/A) , Banvel plus 2 , 4r1) (at 0. 5 + 1 . 0 lb <br /> ai/A) will adequately control musk thistle. However, if these <br /> materials are applied in spring , treatment should occur before <br /> _the weed bolts or some seed will still be produced. Tordon 22K, <br /> Banvel , or Banvel plus 2 ,4-D are also effective .xhen fall <br /> applied. Tordon 22K is the least sensitive of these herbicides <br /> to cool temperatures or droughty conditions . Two relatively'•new <br /> herbicides from Dupont, Telar (chlorsulfuron) and Escort ' ' <br /> (metsulfuron) , also effectively control musk thistle. . However, <br /> these materials can be applied later in spring and still prevent <br /> seed production. Data from 1987 suggests that Telar or Epeort <br /> may be applied as late as early flowering and no seed ip. ' <br /> produced . We are still evaluating timing and rates of jhese <br /> materials. Tordon 22K, Banvel , and 2,4-D are registered for" use <br /> in pastures,rangeland and non-crop; currentlf, ' Telar anO4!scort <br /> are only registered in non-crop areas. <br /> Biological control can be a part of musk thistle management. <br /> The seed head weevil , Rhinocyllus conicus, lary$e destroys musk <br /> thistle seed and is established throughout Colqrado. <br /> Lloyd - We do not recommend Tordon in your situation because of its potential to ipflltrate <br /> into ground water. You should not use Banvel on first year grass sevd'ings. Use 2,4-D <br /> on new seedings only after seedlings have at least 3-4 leaves. The use of trade names <br /> does not imply endorsement of certain pr�4,jcts or criticism of products not named pt <br /> mentioned. WARNING: always read and fr 7 label directions! <br /> Call the office if you have any <br /> y ques. .3-8384 ^ ^ � <br />