2016-07-28_REVISION - M2008006 (2)

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Larimer County Weed List The following 16 weed species are categorized as List B weeds with Colorado Department of Agriculture,and are considered significantly troublesome in Larimer County.These weeds are emphasized in identification and management outreach programs and require management by landowners in the county.For the most part,compliance with county weed law requires prevention of the dispersal of seed,or at a minimum,mowing.The exceptions on the Larimer County list are bull thistle,Scotch thistle and spotted knapweed which are uncommon enough that eradication is possible.County Weed Law requires management methods that prevent seed production of these weeds:pulling,digging,or herbicide application.For effective management of any noxious weed remember: • Weeds are typically opportunistic and readily invade disturbed sites. • Cultural control,the establishment of desirable and competitive vegetation,prevents or slows down invasion by non-native species and is an essential component of successful noxious weed management. • Prevention of new infestations through identification and on-the-spot eradication(early detection and rapid response)saves substantial time and expense. Descriptions,management recommendations and methods of control are listed below. Quick Access to Weeds Canada thistle I Musk thistle I Bull thistle I Scotch thistle Dalmatian toadflax Yellow toadflax 1 Diffuse knapweed I Spotted knapweed Russian knapweed Leafy spurge I Houndstongue I Common teasel I Tamarisk Hoary alyssum Hoary cress Perennial pepperweed Canada thistle (Cirsium arvense) Canada thistle is a deep-rooted perennial that reproduces by seed or underground rootstalks.Seed can remain viable in soil for up to 20 years.Canada thistle originated in Eurasia,was introduced to the U.S.300 years ago,and has become the most =mom common weed problem in the Western United States. r" The most effective herbicides for control of Canada thistle are Perspective,Milestone, Curtail,Redeem,Transline, Tordon,and Telar.Fall C3112tda thl>t„,flt;w't',." applications,prior to a hard frost,are rated best for control T" but any of these listed herbicides applied in the spring or summer provides good control.Because of the extensive underground root system,Canada thistle is very resilient J and eradication requires several seasons of management. r. 1011 Insect agents are available that feed on Canada thistle but have not been Canada thi,,tle rosett,-, proven effective. Canada thistle is palatable to livestock,and grazing can provide suppression through spring and summef. Shallow tillage(disk,sweep)on a deep-rooted perennial can be counter-productive,creating a denser,more uniform stand.