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Dalmatian and yellow toadflax (Linaria genistifolia and dalmatica L.) and (Linaria <br />vulgaris ) are perennials, spreading both by root shoots and seed production. They are <br />very aggressive, forming thick mono -cultures where allowed to grow unimpeded. They <br />are difficult to control due to their extensive root and rhizome system, and in the case of <br />Dalmatian toadflax, a waxy cuticle. Repeated treatments will most likely be necessary <br />before they show any significant improvement. Spray with 1 quart per acre of Tordon or <br />1 quart of Banvel with a quart of 2,4-D amine per acre. Telar and Perspective also <br />provide good control. Round -up is also effective in those areas where grass loss can be <br />tolerated. Surfactant must be used whenever spraying either toadflax. <br />Spotted knapweed (Centaurea maculosa) and diffuse knapweed (Centaurea dffusa) are <br />biennial or short-lived perennial plants. They spread solely by seed production, but can <br />quickly dominate an area. Neither plant is very widespread in Routt County, and when <br />found shall be treated aggressively to prevent their establishment. Milestone is the most <br />effective herbicide available for controlling the knapweeds. Tordon at 24 oz. per acre <br />provides the very good control, but Curtail at 32 oz. per acre or Banvel at 24 oz per acre <br />also work well. Remember, Tordon is a Restricted Use herbicide, requiring a pesticide <br />applicators license from the Colorado Department of Agriculture and tordon persists in <br />the environment for a very long time. <br />Russian „knapweed (Centaurea repens) is a perennial producing by seeds and roots. Best <br />control is achieved by spraying in the spring or fall with 5-7 oz/acre of Milestone. Use a <br />non-ionic surfactant. Another herbicide control is to spray in the spring or fall with 16 oz <br />Tordon + 32 oz. 2,4-D amine per acre with a good quality surfactant. Curtail also <br />provides good control at 1 quart per acre. <br />Le& sure (Euphorbia esula) is a deep rooted perennial, reproducing by seeds, <br />rhizomes and roots. It is one of the most economically and environmentally damaging <br />plants in the West. It is very difficult to control. In the spring spray it with 1 quart of <br />Tordon + 1 quart of 2,4-D amine per acre, or 1 quart of Banvel with 1 quart of 2,4-D <br />amine per acre. Twelve oz of Plateau + methylated seed oil shows good control, but must <br />be sprayed in the fall. As it is essential that no seeds be removed from any site where <br />leafy spurge occurs, this would not provide acceptable control unless the spurge was <br />mowed or grazed to prevent it from going to seed in the summer. Very specific site <br />considerations must be evaluated before treating leafy spurge on riparian sites and it is <br />wise to contact the Routt County Weed Program with any questions regarding herbicide <br />use close to water or in areas with a high water table. <br />