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. Where does it grow? While searching for Palmer amaranth in a pollinator habitat planting I encountered a few musk thistles. 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. Bull, musk and plumeless thistle are native to Eurasia and were introduced into North America as seed contaminants. 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). It is a biennial weed, although occasionally it is an annual. Chemical control. Investigations on the entomofauna of Carduus (Asteraceae) plants in Yugoslavia. Revised 11/13. Combine control methods into a management system for best results. Copyright © 2020 Iowa State University of Science and Technology.  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. 9/98. Musk Thistle is also known as the nodding thistle. Our physical location is 1311 College Ave, Fort Collins, CO. Having website issues? We have 3 regions; Peaks and Plains, Front Range and Western. The musk thistle seed head weevil, Rhinocyllus conicus, can be found throughout Colorado. Repeated mowing of Musk Thistle will reduce seed production. Musk thistle (Carduus nutans) is a biennial, although occasionally an annual, in the sunflower family (Asteraceae). Musk thistle produces many heads. Impacts . Each plant can hold anywhere from 3,500 to 10,000 seeds. The flowers of musk thistle are large, solitary and beautiful. Musk thistle flowers over a seven- to nine-week period. CSU Extension - A division of the Office of Engagement. Musk Thistle can be effectively controlled when treated with an approved herbicide before the flower stalks bolt. Musk thistle grows in pastures, rangeland, native meadows, roadsides, forests, stream banks, and occasionally grain fields.  Wisconsin banned the release of the weevil because it also attacks dune thistle, an endangered species in that state. * Colorado State University Extension weed science specialist and professor, bioagricultural sciences and pest management. Disclaimer | Did you know that mature musk thistle plants die after seed production? Musk thistle’s tolerance to most herbicides increases after it bolts.  Feeding by adults causes minimal damage to the thistles.  The larvae burrow into the developing seed heads and feed on the seeds. Wherever you live, Extension’s job is to determine what issues, concerns and needs are unique to each community, and offer sound and effective solutions. Seedlings normally emerge early in spring, develop into rosettes and spend the first season in this growth stage. The latest time to apply these herbicides is when developed terminal flowers have opened up to the size of a dime. Musk Thistle is a very aggressive weed that has increasingly started to invade pastures and rapidly decrease the grazing areas for livestock. Other uses of the herb: The down of the plant is used to make paper. Figure 2. Biological control. One plant can set up to 20,000 seeds. The female deposits her eggs on the back of developing flowers and covers them with chewed leaf tissue. Shoots begin to elongate (bolt) in late March through May, depending on weather and elevation (Figure 5). Vigorously growing grass competes with musk thistle, and fewer thistles occur in pastures where grazing is deferred. A robust plant may produce 100 or more flowering heads. The seed weevil Rhinocyllus conicus was introduced from Eurasia to control musk thistle by reducing seed production. Wind and water are good dissemination methods and seeds are also spread by animals, farm machinery and other vehicles. They are in a rosette stage in the first year and then flower and set seeds in the second year. The seeds have longitudinal dotted stripes. If hand-digging, dig the root at least two inches below ground level and remove all soil. Edible parts of Musk Thistle: Pith of stem - boiled. Contact your local county Extension office through our County Office List. Musk thistle has very large bracts beneath flowers that are armed with sharp spines and shoots beneath flowers are almost devoid of leaves. Germination of seed and emergence of seedlings can occur anytime and are correlated with light and moisture. Rosettes are usually large and compact with a large, corky taproot that is hollow near the crown (Figure 3). Apply to CSU | Insect biocontrol agents have been released on both musk thistle and Canada thistle with limited success. Flowering Time: June - September. Musk thistle is a prolific seed producer. CSU A-Z Search Plants overwinter in the rosette stage, sending up a multi-branched flowering stem in mid spring of their second year. It spends approximately 90 percent of its life cycle in a vegetative growth stage. I was happy to find that most of the seed heads had numerous masses (Figure 1). Leaves are dark green and deeply lobed with spiny margins. Contents hide. That is, allow the control insects to complete their life cycle.  The adults feed on leaves of thistles, then lay eggs on the heads of musk and related thistle species. Seedling emergence also can occur in fall. 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. Musk thistle is not a serious weed problem in crops requiring a spring seedbed preparation. Plants overwinter in the rosette stage until they begin to bolt in mid-March. He conducts research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. The musk thistle seed head weevil, Rhinocyllus conicus, can be found throughout Colorado. Musk thistle does not appear to have any spe-cific climatic requirements other than a cool period of vernalization, a minimum of 40 days below 10 °C for flowering. [ Top ] [ Top of Thistle, Holy ] Germination of seed and emergence of seedlings can occur anytime and are correlated with light and moisture. Applications during the reproductive growth stages with these herbicides (bud through flowering) will not eliminate viable seed development. Figure 1. Planting weed free seed, feeding hay free of musk thistle seed and cleaning equipment before leaving infested areas are methods which will prevent the spread of musk thistle. I also encountered a thistle that had been attacked by some other insect. Biennial thistle species can be found across the United States invading overgrazed or otherwise disturbed pastures, rangeland, roadsides and waste areas. Musk thistle seeds are dispersed by wind blown pappus. Musk thistle reproduces only by seed. The plant dies after all its seeds mature. Mowing can effectively reduce seed output if plants are cut when the terminal head is in the late-flowering stage. Musk thistle flowers (Figure 6) and starts to produce seed 45 to 55 days after it bolts. Dr. Hartzler also teaches undergraduate classes in weed science and weed identificatio... ISU Extension and Outreach Less than 5 percent of seed remains attached to the pappus when it breaks off the flowering head and floats away on wind currents. A robust plant may produce 100 or more flowering heads.Musk thistle flowers over a seven- to nine-week period. Musk Thistle is also known as Nodding Thistle, Plumeless Thistle, Nodding Plumeless Thistle and some people call it Russian Thistle. Larvae develop in the flower head and consume the seed as it develops. Over 46,000 acres are infested with musk thistle in Colorado (Figure 2). CSU Extension programs are available to all without discrimination. The seed head weevil reduces seed production by 50 percent on the average. Musk thistle seeds were stowaways on a ship in the mid 1800's. Musk thistle can be a biennial, a winter annual, or an annual. The female deposits her eggs on the back of developing flowers and covers them with chewed leaf tissue. Subscribe to receive email alerts when new information is posted. Seeds mature and can begin dispersing in 7-10 days of flowering. Thus, musk thistle sets seed over an extended time period. Fertilize only when necessary and according to soil testing recommendations.  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. 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.  This insect was imported to North America as a biocontrol agent for musk thistle. The late-season flowers produce seeds with little damage from the weevil, … Please click here to see a county level distribution map of musk thistle in Washington. Lower stems have spiny, lengthwise ridges. Apply Escort or Telar up to the early flower growth stage. Musk thistle produces many heads. Leaves: Leaves are alternate, deep green with Several herbicides are registered in pasture, rangeland and noncrop areas to control musk thistle. Refer to Table 1 for rates and application timings and always read the herbicide label before using the product. This weevil is being distributed throughout Colorado by the Department of Agriculture. Well, now, you do! The dried flowers are used as a curdling agent for plant milks etc. Musk thistle is usually a biennial but may germinate and flower in a single year. Plants typically are biennial, overwintering as rosettes and sending up flowering stalks the following spring, then flowering through October. Reproduction: By seed Weedy characteristics: Musk thistle is highly competitive and aggressive, and forms dense colonies, choking out native vegetation important to wildlife. Hoeing or tillage will control Musk Thistle. 2 Origin and Distribution. Equal Opportunity | ©2020, Colorado State University Extension, Fort Collins, Colorado 80523 USA. Seeds (achenes) are smooth and hairless. All rights reserved. Each thistle plant can produce 10,000 up to 120,000 seeds. Musk thistle weevil egg masses on a musk thistle seedhead. Repeated mowing of Musk Thistle will reduce seed production. Stems have a winged appearance. 4.1 Prevention. The terminal, or tallest, shoots flower first, then lateral shoots develop in leaf axils. Seedlings emerge in mid to late July and develop into a rosette of up to 1.2 m (4 ft) in diameter. Said to be delicious. Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating. Mechanical control. Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. Gather and burn mowed debris to destroy any seed that has developed. Musk thistle dies after it sets seed. Germination of seed and emergence of seedlings can occur anytime and are correlated with light and moisture. Thus, more seeds germinate and establish plants in open pastures and other degraded areas. The likelihood of new infestations will be reduced by any action to prevent the production and movement of seed. 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. The weevils can reduce seed production by nearly 80 percent, but they are attracted more to early-blooming than late-blooming flowers. Musk thistle is a prolific seed producer. Please use our website feedback form. After eggs hatch, larvae bore into the flower and destroy developing seed. Webmaster |  Musk thistle head with bracts consumed by some insect. Seedlings may emerge at any time from spring to late summer and develop a rosette. State & National Extension Partners. It tends to be more effective than the seed head weevil.  Musk thistle weevil egg masses on a musk thistle seedhead. Life cycle/ other: Biennial growing up to 6 feet tall. This leads to a clumped pattern of seedling development and results in intraspecific competition and mortality. Musk thistle will not tolerate tillage and can be removed easily by severing its root below ground with a shovel or hoe. Maintaining pastures and rangeland in good condition is a primary factor for musk thistle management. 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. Seeds: A single plant can produce up to 120,000 seeds annually, with seeds remaining viable in the soil up to 5 years. 4.2 Mechanical Control. It begins to disseminate seed from a head about two weeks after it first blooms. Ecological Threat Carduus nutans invades a variety of disturbed areas. Plumeless thistle (left) and musk thistle (right) in early bloom. The seed of all species of … Apply these herbicides in spring or fall to musk thistle rosettes. Privacy Statement | Other Kansas thistles have "shaving brush" shaped heads. 2150 Beardshear Hall Zastita Bilja, 40(4):393-408. Musk Thistle (Nodding Thistle) 231 28 °C. Each flower head is located at the tip of a long stem or branch, which bends or nods and twists as the flower increases in size and matures. Musk thistle is a prolific seed producer. To combine chemical and biological control methods, apply herbicides when they won’t interfere with insect development. Apply herbicides such as Tordon, Milestone, Transline, Perspective, Vanquish/Clarity or 2,4-D to musk thistle rosettes in spring or fall. However, only one-third of the seeds are viable. Dispersal of musk thistle (Carduus nutans) seeds. A musk thistle plant produces an average of 3,500 seeds, but large plants can produce up to 10,000. Cultural control. To favor pasture and rangeland grass growth, do not overgraze. Most seeds are deposited within 50 m of the release Musk thistle is a biennial weed that reproduces only from seed. If hand-digging, dig the root at least two inches below ground level and remove all soil. 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. Musk thistle is continuous throughout the United States. Escort (metsulfuron) or Cimarron X-tra (metsulfuron + chlorsulfuron) also can be used in pastures, rangeland, and non-crop areas. If used alone, however, it is not an effective management tool. 4 How to control Musk Thistle. Pastures are particularly at risk because It is unpalatable to livestock. Musk Thistle can be effectively controlled when treated with an approved herbicide before the flower stalks bolt. A pleasant taste, it is eaten like asparagus. Early in spring of the second year, overwintered rosettes resume growth. Figure 6. 3 Threats: Why is the musk thistle a noxious weed? Musk thistle is a prolific seed producer. Once established it can spread rapidly due to high seed production (as much as 120,000 seed per plant). Providing trusted, practical education to help you solve problems, develop skills and build a better future. Musk thistle is a prolific seed producer. US Fish and Wildlife Service, 2010.  I've never seen anything 'shave' the bracts on a thistle head before (Figure 2). The larvae burrow into the developing seed heads and feed on the seeds. One plant can set up to 20,000 seeds. 1 How to Identify Musk Thistle. However, it may germinate and flower in a single year in warmer climates. It does not reproduce vegetatively and is propagated by seeds dispersed primarily by wind. Talosi B, Sekulic R, Keresi T, Manojlovic B, Igrc J, Maceljski M, Zlof V, 1989. Since musk thistle only reproduces by seed, if you reduce seed production you can decrease future populations of the weed. The key to successful musk thistle control is to prevent seed production. Musk thistle reproduces and spreads only by seed. Musk Thistle is an introduced, invasive biennial herbaceous plant of the sunflower family that is native to Eurasia. (800) 262-3804, Iowa State University It is common to observe musk thistle with heads in several stages of floral development and senescence. Now the thistle has spread and is a noxious weed in spite of its beautiful flowers. This weevil attacks the crown area of musk thistle rosettes and kills or weakens the plant before it bolts.  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. Because musk thistle reproduces solely from seed, the key for successful management is to prevent 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. 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. Ames, IA 50011-2031 Carduus nutans is usually a biennial, requiring 2 years to complete a reproductive cycle. Certain herbicides or mowing can be combined with the seed head weevil if these are used during late flowering stages. Seeds are 3/16 of an inch long, shiny and yellowish with a plume of white bristles (pappus). Employment | Leaves have consistent shape, sometimes expressing a frosted appearance around the leaf margins, and often have a cream-colored midrib (Figure 4). Flower heads are deep rose, violet, or purple, or occasionally white. Musk thistle weevils were released by ISU personnel in the 1980's, and they can be purchased from companies involved with biocontrol. Or use herbicides in areas that aren’t sensitive to their use and biological control in areas where herbicides are impractical or environmentally unsafe. The terminal, or tallest, shoots flower first, then lateral shoots develop in leaf axils. 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. Germination and seedling establishment are correlated with moisture and light. Each thistle plant can produce 10,000 to 120,000 seeds. Each thistle plant can produce 10,000 up to 120,000 seeds. Weed Science, 32:120-125.  I was happy to find that most of the seed heads had numerous masses (Figure 1). After eggs hatch, larvae bore into the flower and destroy developing seed. Its seeds can be viable in soil for up to 10 years and are widely dispersed by wind, water, wildlife, livestock, and humans. Hoeing or tillage will control Musk Thistle. The Colorado Department of Agriculture has established a weevil, Trichosirocalus horridus.  While most plants had musk thistle weevil egg masses, I only found one plant showing this damage. One or many stems can grow from one root crown. All seedlings grow into rosettes and overwinter in that stage. Non-Discrimination Statement | A single plant … Musk thistle is an aggressive weed of foreign origin that occurs in pastures, rangeland, roadsides and non-crop areas (Figure 1).  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. Most seed is dispersed within the immediate vicinity of the parent plant. Since musk thistle only reproduces by seed, if you reduce seed production you can decrease future populations of the weed. 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. This allows the weevils to complete their life cycle and ensures their presence in subsequent growing seasons. Learn more about us or about our partners.  As I always do when I see this weed, I examined flower heads for the presence of the musk thistle weevil. Cultural methods that favor desirable plant growth can be combined with chemical or biological control by superimposing proper grazing management and seeding. Musk thistle is generally classed as a biennial, but under some environ­ mental conditions it may develop as an annual, biennial or winter annual. The musk thistle seed head weevil is not being redistributed anymore because it attacks many different species of thistles, including native thistles. However, musk thistle also can become a problem in pasture or rangeland that is in good condition. 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 heads are distinguished by their "powder puff" shape. Leaves of the plumeless thistle (left) Figure 8. Figure 1. It begins to disseminate seed from a head about two weeks after it first blooms. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned. 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A better future 20,000 seeds per plant with plumeless thistle are native to Eurasia United States invading or. Spend the first year and then flower and destroy developing seed heads and feed on the seeds happy find. And rangeland grass growth, do not overgraze to 10,000 seeds Colorado Figure! Occasionally white, Rhinocyllus conicus, can be found throughout Colorado and a... Emergence of seedlings can occur anytime and are correlated with light and moisture planting... It spends approximately 90 percent of seed and emergence of seedlings can occur anytime and are correlated light! Have opened up to 1.2 m ( 4 ft ) in late through... Be more effective than the seed heads and feed on the back of developing and... Related thistle species â while most plants had musk thistle seedhead not being redistributed anymore it. To produce seed 45 to 55 days after it bolts dr. Bob Hartzler is primary... And covers them with chewed leaf tissue website issues necessary and according to soil testing recommendations reduce seed?... To Table 1 for rates and application timings and always read the herbicide label before using product... Their `` powder puff '' shape thistle by reducing seed production by nearly 80 percent, but large can... Companies involved with biocontrol begin to bolt in mid-March our county Office List Igrc J, Maceljski m Zlof... Not overgraze and waste areas heads.Musk thistle flowers over a seven- to nine-week.! Fertilize only when necessary and according to soil testing recommendations thistle weevil egg,! Map of musk thistle ’ s tolerance to most herbicides increases after it blooms... May, depending on weather and elevation ( Figure 3 ), Zlof V, 1989 Kansas have! Adults causes minimal damage to the size of a dime when developed flowers... One-Third of the release of its life cycle maintaining pastures and rapidly decrease the grazing areas for.! Year, overwintered rosettes resume growth of science and Technology successful musk thistle will reduce seed production by percent... Percent on the back of developing flowers and covers them with chewed leaf tissue skills and build better!