Biennial thistle species can be found across the United States invading overgrazed or otherwise disturbed pastures, rangeland, roadsides and waste areas. However, only one-third of the seeds are viable. The weevils can reduce seed production by nearly 80 percent, but they are attracted more to early-blooming than late-blooming flowers. The key to successful musk thistle control is to prevent seed production. 2150 Beardshear Hall Early in spring of the second year, overwintered rosettes resume growth. The latest time to apply these herbicides is when developed terminal flowers have opened up to the size of a dime. The late-season flowers produce seeds with little damage from the weevil, … CSU Extension - A division of the Office of Engagement. This weevil is being distributed throughout Colorado by the Department of Agriculture.  In my random examinations of musk thistle patches over the past decades I would estimate that musk thistle weevil is present at more than half of the locations. This leads to a clumped pattern of seedling development and results in intraspecific competition and mortality. Musk thistle can be a biennial, a winter annual, or an annual. Seedling emergence also can occur in fall. Contact your local county Extension office through our County Office List.  This insect was imported to North America as a biocontrol agent for musk thistle. Gather and burn mowed debris to destroy any seed that has developed. However, it may germinate and flower in a single year in warmer climates. If hand-digging, dig the root at least two inches below ground level and remove all soil. Figure 1. Musk thistle is an aggressive weed of foreign origin that occurs in pastures, rangeland, roadsides and non-crop areas (Figure 1). Musk thistle has very large bracts beneath flowers that are armed with sharp spines and shoots beneath flowers are almost devoid of leaves. Pastures are particularly at risk because It is unpalatable to livestock. Apply herbicides such as Tordon, Milestone, Transline, Perspective, Vanquish/Clarity or 2,4-D to musk thistle rosettes in spring or fall. Wind and water are good dissemination methods and seeds are also spread by animals, farm machinery and other vehicles. [ Top ] [ Top of Thistle, Holy ] Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating. CSU Horticulture Agents and Specialists Blog, Capric Acid: A Promising Next-Generation Herbicide for Organic Specialty Crop Production, Columnar and Fastigiate Trees for CO Landscapes, Management-intensive Grazing (MiG) on Irrigated Pasture, Pulse Crops and their Key Role as Staple Foods in Healthful Eating Patterns, Integrated Hive Management for Colorado Beekeepers, Management-intensive Grazing (MiG) and Soil Health, Spring at rosette growth stage; or in fall, Use higher rates for older or dense stands, Use higher rate for older or dense stands; may be used to edge ponds or streams, Spring at rosette to early bolting growth stages; or in fall, Use higher rate for older or dense stands, Spring rosette to early bud growth stages; or to fall rosettes, Spring to rosette to early bud growth stages; or to fall rosettes. If hand-digging, dig the root at least two inches below ground level and remove all soil. Musk thistle’s tolerance to most herbicides increases after it bolts. Musk Thistle is also known as the nodding thistle.  Iowa's fractured landscape prevents expansive infestations of musk thistle, therefore the biocontrol agent doesn't build up to populations that provide a high level of control. The seeds have longitudinal dotted stripes. This weevil attacks the crown area of musk thistle rosettes and kills or weakens the plant before it bolts. Cultural methods that favor desirable plant growth can be combined with chemical or biological control by superimposing proper grazing management and seeding. Combine control methods into a management system for best results. This allows the weevils to complete their life cycle and ensures their presence in subsequent growing seasons. A musk thistle plant produces an average of 3,500 seeds, but large plants can produce up to 10,000. Mechanical control. Impacts . Dr. Hartzler also teaches undergraduate classes in weed science and weed identificatio... ISU Extension and Outreach All seedlings grow into rosettes and overwinter in that stage. Where does it grow? Webmaster | A robust plant may produce 100 or more flowering heads.Musk thistle flowers over a seven- to nine-week period. Ames, IA 50011-2031 Our physical location is 1311 College Ave, Fort Collins, CO. Having website issues? Each thistle plant can produce 10,000 up to 120,000 seeds. Musk thistle seeds are dispersed by wind blown pappus. Most seed is dispersed within the immediate vicinity of the parent plant.  As I always do when I see this weed, I examined flower heads for the presence of the musk thistle weevil. Apply Escort or Telar up to the early flower growth stage. One plant can set up to 20,000 seeds. Subscribe to receive email alerts when new information is posted.  While the weevil obviously isn't eliminating musk thistle from the Iowa landscape, I believe its presence reduces thistle populations from where they would be if the weevil wasn't feeding on seedheads. The terminal, or tallest, shoots flower first, then lateral shoots develop in leaf axils. A robust plant may produce 100 or more flowering heads. Repeated mowing of Musk Thistle will reduce seed production. Musk Thistle is a very aggressive weed that has increasingly started to invade pastures and rapidly decrease the grazing areas for livestock. Plumeless thistle (left) and musk thistle (right) in early bloom. Each plant can hold anywhere from 3,500 to 10,000 seeds. Well, now, you do! Less than 5 percent of seed remains attached to the pappus when it breaks off the flowering head and floats away on wind currents. Seeds: A single plant can produce up to 120,000 seeds annually, with seeds remaining viable in the soil up to 5 years. Musk Thistle is also known as Nodding Thistle, Plumeless Thistle, Nodding Plumeless Thistle and some people call it Russian Thistle. 9/98. Musk thistle is usually a biennial but may germinate and flower in a single year. Weed Science, 32:120-125. * Colorado State University Extension weed science specialist and professor, bioagricultural sciences and pest management. Musk thistle is not a serious weed problem in crops requiring a spring seedbed preparation. Musk thistle weevil egg masses on a musk thistle seedhead. Musk thistle is a prolific seed producer. Musk thistle produces many heads. Disclaimer | Germination and seedling establishment are correlated with moisture and light. Flowering Time: June - September. Maintaining pastures and rangeland in good condition is a primary factor for musk thistle management. It begins to disseminate seed from a head about two weeks after it first blooms. Musk thistle produces many heads. Optimum germination will take place in moist soil with 59 to 68 degrees F soil temperature in the light and 68 to 86 degrees F in the dark. That is, allow the control insects to complete their life cycle. Seedlings normally emerge early in spring, develop into rosettes and spend the first season in this growth stage. (800) 262-3804, Iowa State University Control Said to be delicious. Leaves have consistent shape, sometimes expressing a frosted appearance around the leaf margins, and often have a cream-colored midrib (Figure 4). A pleasant taste, it is eaten like asparagus. Please click here to see a county level distribution map of musk thistle in Washington. Rosettes are usually large and compact with a large, corky taproot that is hollow near the crown (Figure 3). The seed of all species of … Refer to Table 1 for rates and application timings and always read the herbicide label before using the product. To successfully manage musk thistle, prevent seed formation. Several herbicides are registered in pasture, rangeland and noncrop areas to control musk thistle. Musk thistle is a prolific seed producer. Investigations on the entomofauna of Carduus (Asteraceae) plants in Yugoslavia. Germination of seed and emergence of seedlings can occur anytime and are correlated with light and moisture. Nodding Thistle aka Musk Thistle (Carduus nutans) Provincial Designation: Restricted Identification: Stems: First year forms a large rosette; sec-ond year grows between 20cm up to 2.5 m tall. Ecological Threat Carduus nutans invades a variety of disturbed areas. However, only one-third of the seeds are viable. Larvae develop in the flower head and consume the seed as it develops. ©2020, Colorado State University Extension, Fort Collins, Colorado 80523 USA. Copyright © 2020 Iowa State University of Science and Technology. Each thistle plant can produce 10,000 up to 120,000 seeds. Since musk thistle only reproduces by seed, if you reduce seed production you can decrease future populations of the weed. Privacy Statement | Learn more about us or about our partners. Figure 6. After eggs hatch, larvae bore into the flower and destroy developing seed. The seeds of the Milk Thistle (Carduus Marianus), known also as Silybum Marianum, have similar properties and uses, and the Cotton Thistle, Melancholy Thistle, etc., have also been employed for like purposes. Spreading by seed only and producing 8,400 seeds per plant with plumeless thistle to 20,000 seeds per plant from musk thistle. Musk thistle reproduces only by seed.  The adults feed on leaves of thistles, then lay eggs on the heads of musk and related thistle species.  The musk thistle weevil will lay eggs on seedheads of several biennial thistles, but 'prefers' musk thistle since this species flowers at the same time as egg laying of the weevil. 2 Origin and Distribution. One plant can set up to 20,000 seeds. Its seeds can be viable in soil for up to 10 years and are widely dispersed by wind, water, wildlife, livestock, and humans. Plants overwinter in the rosette stage, sending up a multi-branched flowering stem in mid spring of their second year. A single plant … The likelihood of new infestations will be reduced by any action to prevent the production and movement of seed. Thus, more seeds germinate and establish plants in open pastures and other degraded areas. Musk thistle heads are distinguished by their "powder puff" shape. Research from Colorado State University and the University of Nebraska shows that chlorsulfuron or metsulfuron prevents or dramatically reduces viable seed formation when applied in spring, up to early flower growth stages. Over 46,000 acres are infested with musk thistle in Colorado (Figure 2). Musk thistle is generally classed as a biennial, but under some environ­ mental conditions it may develop as an annual, biennial or winter annual. Leaves are dark green and deeply lobed with spiny margins. Smith LM, Kok LT, 1984. The musk thistle seed head weevil, Rhinocyllus conicus, can be found throughout Colorado. Now the thistle has spread and is a noxious weed in spite of its beautiful flowers. Germination of seed and emergence of seedlings can occur anytime and are correlated with light and moisture. The seed head weevil reduces seed production by 50 percent on the average. It does not reproduce vegetatively and is propagated by seeds dispersed primarily by wind. One or many stems can grow from one root crown. Musk thistle flowers (Figure 6) and starts to produce seed 45 to 55 days after it bolts. Optimum germination will take place in moist soil with 59° to 68°F soil temperature in the light and 68° to 86°F in the dark. Add a good agricultural surfactant at 0.25 percent v/v to Escort or Cimarron X-tra treatments or control is inadequate (equivalent to 1 quart of surfactant per 100 gallons of spray solution). They are in a rosette stage in the first year and then flower and set seeds in the second year. Mowing can effectively reduce seed output if plants are cut when the terminal head is in the late-flowering stage. Musk thistle weevils were released by ISU personnel in the 1980's, and they can be purchased from companies involved with biocontrol. 4.2 Mechanical Control. Providing trusted, practical education to help you solve problems, develop skills and build a better future. Applications during the reproductive growth stages with these herbicides (bud through flowering) will not eliminate viable seed development. All rights reserved.  Musk thistle weevil egg masses on a musk thistle seedhead. Seeds (achenes) are smooth and hairless. Thus, musk thistle sets seed over an extended time period. Musk Thistle is an introduced, invasive biennial herbaceous plant of the sunflower family that is native to Eurasia. Equal Opportunity | Thistle—whether it's of the musk, tall or Canada variety—is a very difficult weed to eliminate from your lawn or garden once it has taken hold; a single musk thistle can generate 120,000 seeds from one flower, and can grow to six feet tall. To combine chemical and biological control methods, apply herbicides when they won’t interfere with insect development. The larvae burrow into the developing seed heads and feed on the seeds. Musk thistle dies after it sets seed.  I've never seen anything 'shave' the bracts on a thistle head before (Figure 2). The musk thistle seed head weevil, Rhinocyllus conicus, can be found throughout Colorado. Plants typically are biennial, overwintering as rosettes and sending up flowering stalks the following spring, then flowering through October. Vigorously growing grass competes with musk thistle, and fewer thistles occur in pastures where grazing is deferred. Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. It is a biennial weed, although occasionally it is an annual. Germination of seed and emergence of seedlings can occur anytime and are correlated with light and moisture. Seeds mature and can begin dispersing in 7-10 days of flowering. 1 How to Identify Musk Thistle. Bull, musk and plumeless thistle are native to Eurasia and were introduced into North America as seed contaminants. Apply these herbicides in spring or fall to musk thistle rosettes. Or use herbicides in areas that aren’t sensitive to their use and biological control in areas where herbicides are impractical or environmentally unsafe. Apply to CSU | Contents hide. Musk Thistle can be effectively controlled when treated with an approved herbicide before the flower stalks bolt. Each thistle plant can produce 10,000 to 120,000 seeds. Musk Thistle can be effectively controlled when treated with an approved herbicide before the flower stalks bolt. Revised 11/13. However, musk thistle also can become a problem in pasture or rangeland that is in good condition. Musk thistle is a prolific seed producer. It tends to be more effective than the seed head weevil. The dried flowers are used as a curdling agent for plant milks etc. Stems have a winged appearance. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned. US Fish and Wildlife Service, 2010.  Musk thistle head with bracts consumed by some insect.  Feeding by adults causes minimal damage to the thistles.  The larvae burrow into the developing seed heads and feed on the seeds. Seedlings may emerge at any time from spring to late summer and develop a rosette. Figure 1. Chemical control. Each flower head, depending on the size, can produce anywhere from 200 to 3,000 seeds by midsummer and an entire plant can produce more than 10,000 seeds. We have 3 regions; Peaks and Plains, Front Range and Western. Musk Thistle (Nodding Thistle) 231 28 °C. The seed weevil Rhinocyllus conicus was introduced from Eurasia to control musk thistle by reducing seed production. Tordon 22K (picloram), Milestone (aminopyralid), Transline (clopyralid), Perspective (aminocyclopyrachlor + chlorsulfuron), Banvel/Vanquish/Clarity (dicamba), 2,4-D, or Banvel/Vanquish/Clarity plus 2,4-D are commonly used. 4.1 Prevention. Please use our website feedback form. The female deposits her eggs on the back of developing flowers and covers them with chewed leaf tissue. Musk Thistle is a biennial weed that is reproduced by the release of its seeds and has a two year life span. Fertilize only when necessary and according to soil testing recommendations. Seedlings emerge in mid to late July and develop into a rosette of up to 1.2 m (4 ft) in diameter. Figure 2. Carduus nutans is usually a biennial, requiring 2 years to complete a reproductive cycle. Musk thistle flowers over a seven- to nine-week period. Escort (metsulfuron) or Cimarron X-tra (metsulfuron + chlorsulfuron) also can be used in pastures, rangeland, and non-crop areas. Repeated mowing of Musk Thistle will reduce seed production. Other uses of the herb: The down of the plant is used to make paper. Musk thistle reproduces and spreads only by seed. I was happy to find that most of the seed heads had numerous masses (Figure 1). Reproduction: By seed Weedy characteristics: Musk thistle is highly competitive and aggressive, and forms dense colonies, choking out native vegetation important to wildlife. The Colorado Department of Agriculture has established a weevil, Trichosirocalus horridus. The terminal, or tallest, shoots flower first, then lateral shoots develop in leaf axils. Musk thistle’s most distinguishing factor is its flowers, which grow up to 1 to 2 inches in diameter and are usually puffy with purplish hues. CSU Extension programs are available to all without discrimination. Insect biocontrol agents have been released on both musk thistle and Canada thistle with limited success. Hoeing or tillage will control Musk Thistle. 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