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Musk Thistle Carduuas nutans |
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Keys to Identification:
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This information courtesy of the Colorado Natural Areas Program Family: Asteraceae (Sunflower) Other Names: nodding thistle, nodding plumeless thistle USDA Code: CANUM2 Legal Status: Colorado Noxious Weed List B Identification Lifecycle: Biennial, or sometimes winter annual Growth form: Forb Flower: Flower heads are terminal, solitary, 1.5 to 3 inches in diameter, and usually nodding. Flowers are deep rose, violet or purple, occasionally white. Flowers are subtended by broad, spine-tipped bracts. Seeds/Fruit: One-seeded oblong fruit (achene) about 0.2 inches long, shiny, yellowish-brown with a plume (pappus) of white hair-like bristles. Leaves: Leaves are alternate, dark green, deeply lobed, and spiny margined. The leaves extend onto the stem giving a winged appearance (Whitson et al. 1996). Basal rosettes are well developed, leaves elliptical to lanceolate, 6-14 inches, smooth to densely hairy. Stems: Mature plants can grow as tall as 6 feet. It can appear solitarily or with several stems from one base, and is highly branched above. Roots: Fleshy taproot Similar Species Exotics: Musk thistle is similar to plumeless thistle (Carduus acanthoides). Rosettes of plumeless thistle are distinguished from those of musk thistle by having leaves that are deeply serrate (saw-toothed) almost to the midrib. Natives: There are many native thistle species (in the genus Cirsium). The natives generally do not have leaves clasping the stem all the way from node to node (strongly decurrent leaves), and many have hairy upper and lower leaf surfaces and are blue-green or gray in color. Impacts Agricultural: Likely to infest pastures. Is unpalatable to livestock. Ecological: Musk thistle is a highly competitive weed which invades disturbed areas, pasture, rangeland, forest land, cropland, and waste areas throughout most of the United States. Musk thistle spreads rapidly and forms extensive stands, which force out desirable vegetation (Rutledge and McLendon, 1998). Musk thistle may produce allelopathic chemicals that inhibit desirable plants beyond the spread of the rosettes (Wardle et al. 1993). Habitat and Distribution General requirements: Musk thistle does not appear to have any specific climatic requirements other than a cool period of vernalization for flowering (Butterfield et al. 1996). It occurs in areas with as little as 10 inches of annual precipitation (FEIS 1998). Musk thistle establishes best on bare soil, and small shallow cracks are ideal for seedling establishment (FEIS 1998). Musk thistle grows in all soil textures, but the soils must be well-drained (Butterfield et al. 1996) It occurs on soils with a pH range of 6.0 to 8.9 (Butterfield et al. 1996). Distribution: In Colorado, musk thistle is found up to approximately 10,000 feet in elevation (Beck 1999). It is found throughout North America. Historical: Native to Eurasia. Biology/Ecology Life cycle: Seeds germinate in the fall, forming a rosette of leaves. Typically, musk thistle over-winters as a rosette and bolts the following spring between April-June. Flowering begins in late May or early June and continues through mid-July (Butterfield et al. 1996). Seeds mature and are dispersed 1 to 3 weeks after flowering. Seedlings establish only on bare soils and grow less when shaded by neighboring plants (Beck 1999). Mode of reproduction: Musk thistle reproduces solely by seed. Seed production: Musk thistle is a prolific seed producer Average productivity is approximately 10,000 seeds/plant, however, a single plant can produce up to 100,000 seeds (Beck 1999). Seed bank: Musk thistle seeds appear to remain viable for at least 10 years. Dispersal: Seed dispersal is by wind water, wildlife and livestock (Beck 1999). Hybridization: May hybridize with plumeless thistle (Carduus acanthoides). Integrated Management Summary The key to managing musk thistle is to prevent seed production. Most control methods will have a detrimental effect on other plants and may cause a disturbance that will favor re-invasion by other exotic species (Rutledge and McLendon, 1998). Dense musk thistle stands along roadsides and in degraded areas can be treated by spot use of herbicides, and in high-quality areas by a persistent program of pulling or cutting (Rutledge and McLendon, 1998). Due to the long seed viability of musk thistle, up to 10 years, control methods may have to be repeated for many years to completely eliminate a stand. One integrated approach to musk thistle management involves 1) managing livestock grazing to increase grass vigor and reduce bare ground; 2) spray rosettes with clopyralid or 2,4-D; 3) re-seed treated ground with competitive desirable plants in the fall after spraying; 4) follow-up with spot cutting of entire plants when first flowers appear annually for several years to deplete the seed bank in the soil. CONTROL References
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