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.~-;~ : ~ ~ ~ • ~~o III IIIIIIIIIIIII III ~, ~ Umaersin Cooperati~~e Extension Colorado Statc Cnivcrsit) Fort Collins, C<dorado Flli_i January 16, 1988 Mr. Terrel Johnson Yampa Valley Coal Co. 29588 RCR (r29 Oak Creek, CO 80467 Dear Mr. Johnson: Jim Stanko, Routt County Extension, asked that I write you and provide information about herbicides that will control several weeds (Canada thistle, poison hemlock, houndstongue, cluster tarweed, catchweed bedstraw, and sagebrush). He also indicated that you desired information in addition to that found in the Pest Control Guide (i.e., 2,4-D and Banvel, and Tordon) such as Telar. Telar is a relatively new herbicide that inhibits an enzyme that catalyzes the biosynthesis of aromatic amino acids in plants. If plants cannot produce these amino acids (valine and isoleucine), protein synthesis is incomplete and plants quit growing and die. Telar will readily control Canada thistle, catchweed bedstraw (stick tights) if applied at 1 oz of product per acre. However, timing for Canada thistle control is critical; applications should be made when Canada thistle is in the bud stage or best control is achieved when applied in fall. Also, we have found that treating Canada thistle in late spring (about mid- to late-June) with 2 lb ai/A of 2,4-D followed by 1 oz of Telar in fall provides excellent control for at least two seasons. Telar control of Canada thistle is very slow; do not look for symptoms similar to 2,4-D or Banvel. Canada thistle treated with Telar will become chlorotic (turn yellow), eventually turr. brown and die. It may take an entire growing season for results to be seen. Telar should be applied to catchweed bedstraw in spring. Telar will not control the other weeds you listed. Telar is a non-crop herbicide and cannot be used on pasture or rangeland. Tordon 22K is very cost effective to use even though it is restricted use and one has to be licensed to apply it. Tordon is registered for use in permanent pastures, rangeland, and non-crop thus, you could use it in more areas than Telar. Tordon 22K (applied at 1 lb ai/A) is equally effective on Canada thistle as Telar and Tordon can be applied anytime Canada thistle is actively growing (from early spring through fall). However, Canada thistle is best controlled with any herbicide when applied in fall (e.g. late August to September depending on weather). Houndstongue and catchweed bedstraw also are readily controlled Colorado Statc University, U.S. Ikpartment of Agriculture and Colorado counties cooperating. Coopera[Ive Extension programs arc available [o all x~ithout discrimination.