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INTEGRATED WEED MANAGEMENT of MUSK THIS! [..E for large lot owners, farmers, and ranchers. No single control method should be used in managing weeds. A combination of methods (IPM) should be used. An integrated pest management plan deals with prevention as well as control. Eradication of weed species is often not a practical goal but in most cases reducing infestation to manageable levels should be the objective. MUSK TFIISTLE (Carduus nutans) is biennial or sometimes a winter annual, which grows up to six Ceet tall. Leaves are dark green with light green midrib, deeply lobed, spiny marginate. Edge of leaves are often agrayish-silver color. The leaves extend on-o the stem giving a winged appearance. Flower is terminal, solitary, 1 1/2 - 3 inches in diameter. It is usually bent over. I-lowers are deep rose, violet, or purple, occasionally while; they are subtended by long narrow, spine-tipped bracts. Cultural Plant wmpetition is an effective way to prevent the invasion of musk thistle. Proper management of perennial grasses will inhibit the establishment o[ this weed. Overgrazing is a major cause of perennial weed invasion. In Douglas County, one horse requires 35 to 40 acres oC pasture land if no supplemental Coed is provided. Residents should consider the above facts when planning recreational or hobby activities as it pertains to horses. A general rule of thumb to prevent overgrazing, is the take-half leave- half principle. A stand of grass will maintain or even improve its condition iC no more than one-half of its annual production is used. In other words, animals could graze until, on average, fifty percent of the grass has been utilized. Animals would then be removed until the vegetation recovers its original height. Other cultural methods include: • fertilization when necessary (A soil test is the best way to determine fertilization on a site, Contact the Douglas County Extension Of(ice for soil test kits.) • water management • where the perennial vegetation has been depleted, reseeding adapted varieties is recommended • disturbed areas should be revegetaled as soon as possible prevent weed invasions Biological Insects are being utilized as a means for long-term management of weeds. In Colorado, insects have been released on an experimental basis to control musk thistle. At this time, some are available to the general public. The Head weevil is found throughout Douglas County, but consumes only about 50% of the possible 20,000 seeds that a musk thistle produces. This weevil was released in 1974 and is established throughout Colorado. The insect feeds in developing seeds thus preventing the plant from reproducing. Another weevil feeds on the musk thistle rosette. Additional head weevils are about $20/500 & the rosette weevils are around $50/100. The head weevils should be released in May and/or June, and the rosette weevil in July. Mechanical Mowing will not kill the plant but will lessen the seed production if it keeps the seed heads Crom maturing. Small areas can be eradicated if the land owner digs all the plants on his property. The plants must be cut off below the soil surface and no leaves can remain attached or it will grow back. In addition, reduced vegetative matter Crom mowing will allow fall herbicide use to be more elleclive. Chemical Landowners should treat with extra care so as to prevent contamination of water sources and off-target damage (gardens, or desirable trees. The following are some options Cor chemical treatments of ptusk thistle: • 2,4-D (around trees and shallow water tables) at 2gts/acre in the rosette stage in the spring and a fall treatment of new seedlings. • Roundup @ 1/2 gallon/acre in the spring at the bloom stage. a ••I