Problem Thistles of Oregon, EC 1288

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PROBLEM THISTLES OF OREGON EC 1288 / Revised December 2006 hese thistles are native to control program. Know your enemy. Yellow Bull thistle Canada thistle Europe and the Middle East. Effective control of a perennial thistle, starthistle Cirsium vulgare Cirsium arvense Some are not true thistles; for such as Canada thistle, differs greatly from Centaurea Life cycle. Bien- Life cycle. Creep- example, purple/Iberian and control of the similar-looking, but annual, solstitialis nial, sometimes ing perennial. Tyellow starthistle actually are knap- Italian thistle. Key characteristics to look annual. Flowers. Light Life cycle. Flowers. Purple, purple to white, weeds. All of these plants, however, for are flower color and size and time of Annual that germi- 1 1 3 2 ⁄2 to ⁄4 inch in diame- nates in fall, winter, 1 ⁄ to 2 inches in share a spiny, thorny, invasive nature bloom. ter, borne at the tips of or spring, depend- diameter, often and long-lasting, hard seed. These Early detection and control of new the branches, often in ing on soil distur- clustered at the ends traits make people who use or man- infestations is essential to keep Oregon clusters. Flowers July bances and moisture of branches. Flow- through August. age land for recreation, wildlife, or from being overrun by these and other availability. ers July through Description. The livestock very concerned. We need to noxious weeds. Flowers. Bright September. 1 3 Description. Bull smooth stems are from act now to protect Oregon’s precious yellow, ⁄2 to ⁄4 inch 1 to 4 feet tall, erect and ridged. The leaves are in diameter, usually thistle forms a spiny agricultural and natural areas. edged with stiff, yellowish spines. Life cycles occurring singly rosette the first year; Bull and Canada thistles have been How it spreads. Mostly by extensive, The plants we discuss in this publica- at the top of each the many-branched branching root systems. Also by seeds. established in Oregon for many years. tion are classified as annuals, winter annu- branch. Blooms July stem is formed the The problem. Canada thistle differs from Consequently, they’re widespread als, biennials, or perennials. These terms through October. second year. The other true thistles in that the flowers are unisex- in the state. Others have been estab- Description. leaves are deeply describe the normal growth habits of ual, with male and female flowers on separate Actually a knapweed; lobed, hairy above lished long enough to become severe these weeds, but exceptions are common. plants. Its colony-forming nature, coupled with the spines on yel- and cottony below. problems, but in limited areas. Distaff its deep and extensive horizontal root system, When a biennial is clipped in its second low starthistle are Spiny wings are thistle has been identified in Oregon can lead to infestations of same-sex plants that year, for example, the plant may function straw-colored, about formed on the stem only since 1987, purple/Iberian 3 of the prickly leaf do not produce seed but still are extremely as a short-term perennial. Winter annu- ⁄4 inch long, and are invasive and persistent. It grows in a wide range starthistle since 1993. around the blooms. base. als may germinate in the spring instead of of environments. Cultivation breaks up roots, Most of these thistles have a par- The rest of the plant How it spreads. fall and act as biennials. Soil disturbance which can form new plants and subsequent is covered with short, Seeds often are blown ticular niche in the environment that and availability of moisture and sunlight colonies. cottonlike hairs that a long distance by they exploit to their advantage and Distribution. Prefers deeper, richer soils usually are the determining factors. give the foliage a wind. than many thistles. Canada thistle occurs in at the expense of other vegetation. In For assistance in identifying or con- characteristic grayish- The problem. every county in Oregon. North America, they don’t have the trolling these or other noxious weeds, green appearance. Bull thistle has been present in Oregon since great complex of insects and diseases Leaves sometimes extend down the stem, giving before 1900. It occurs along roadsides, in waste contact: areas, meadows, and forest clearcuts. It can form that evolved with them overseas. Free • Oregon Department of Agriculture, a “winged” or flattened appearance. How it spreads. Rapidly by seeds, as many dense stands in pastures that are in poor condi- from such pests, they are much more Noxious Weed Control Program tion. Promoting the health and vigor of grasses competitive in this country than in as 150,000 from a single large plant. 635 Capitol St. N.E., Salem, OR 97301 The problem. Yellow starthistle grows in a and forage through fertilization and rotational their native range. Phone: 503-986-4621 wide range of environments. It favors dry range grazing can make pastures much less susceptible Oregon is extremely vulnerable and pastures, where its sharp spines discour- to bull thistle invasion. Web: oregon.gov/ODA/PLANT/WEEDS Distribution. Bull thistle occurs in every to further invasion by thistles. Sev- age livestock grazing. Feeding on this plant can © 2006 Oregon State University • Your local Oregon State University county in Oregon. eral thistles are so well established Extension Service office cause susceptible horses to develop a nervous This publication was produced and distributed in furtherance in particular areas that eradication is system disorder called “chewing disease,” which of the Acts of Congress of May 8 and June 30, 1914. Extension • Your county weed program supervisor usually results in death because the horse is work is a cooperative program of Oregon State University, the not possible. However, much suitable unable to eat or drink. U.S. Department of Agriculture, and Oregon counties. habitat in Oregon is open to invasion Report new suspect invasions by Distribution. Major infestations occur in Oregon State University Extension Service offers educational and needs to be protected. Jackson, Josephine, Douglas, Baker, and Wheeler programs, activities, and materials without discrimination based calling the Invasive Species Hotline: on age, color, disability, gender identity or expression, marital counties, with sizable infestations present in Thistle identification is key to plan- 1-866-INVADER. status, national origin, race, religion, sex, sexual orientation, or ning and implementing an effective Umatilla County. Smaller infestations occur in veteran’s status. Oregon State University Extension Service is an Wasco, Sherman, Morrow, and Gilliam counties. Equal Opportunity Employer. Major infestations also occur in California. Published March 1989. Revised December 2006. PROBLEM THISTLES OF OREGON EC 1288 / Revised December 2006 hese thistles are native to control program. Know your enemy. Yellow Bull thistle Canada thistle Europe and the Middle East. Effective control of a perennial thistle, starthistle Cirsium vulgare Cirsium arvense Some are not true thistles; for such as Canada thistle, differs greatly from Centaurea Life cycle. Bien- Life cycle. Creep- example, purple/Iberian and control of the similar-looking, but annual, solstitialis nial, sometimes ing perennial. Tyellow starthistle actually are knap- Italian thistle. Key characteristics to look annual. Flowers. Light Life cycle. Flowers. Purple, purple to white, weeds. All of these plants, however, for are flower color and size and time of Annual that germi- 1 1 3 2 ⁄2 to ⁄4 inch in diame- nates in fall, winter, 1 ⁄ to 2 inches in share a spiny, thorny, invasive nature bloom. ter, borne at the tips of or spring, depend- diameter, often and long-lasting, hard seed. These Early detection and control of new the branches, often in ing on soil distur- clustered at the ends traits make people who use or man- infestations is essential to keep Oregon clusters. Flowers July bances and moisture of branches. Flow- through August. age land for recreation, wildlife, or from being overrun by these and other availability. ers July through Description. The livestock very concerned. We need to noxious weeds. Flowers. Bright September. 1 3 Description. Bull smooth stems are from act now to protect Oregon’s precious yellow, ⁄2 to ⁄4 inch 1 to 4 feet tall, erect and ridged. The leaves are in diameter, usually thistle forms a spiny agricultural and natural areas. edged with stiff, yellowish spines. Life cycles occurring singly rosette the first year; Bull and Canada thistles have been How it spreads. Mostly by extensive, The plants we discuss in this publica- at the top of each the many-branched branching root systems. Also by seeds. established in Oregon for many years. tion are classified as annuals, winter annu- branch. Blooms July stem is formed the The problem. Canada thistle differs from Consequently, they’re widespread als, biennials, or perennials. These terms through October. second year. The other true thistles in that the flowers are unisex- in the state. Others have been estab- Description. leaves are deeply describe the normal growth habits of ual, with male and female flowers on separate Actually a knapweed; lobed, hairy above lished long enough to become severe these weeds, but exceptions are common. plants. Its colony-forming nature, coupled with the spines on yel- and cottony below. problems, but in limited areas. Distaff its deep and extensive horizontal root system, When a biennial is clipped in its second low starthistle are Spiny wings are thistle has been identified in Oregon can lead to infestations of same-sex plants that year, for example, the plant may function straw-colored, about formed on the stem only since 1987, purple/Iberian 3 of the prickly leaf do not produce seed but still are extremely as a short-term perennial. Winter annu- ⁄4 inch long, and are invasive and persistent. It grows in a wide range starthistle since 1993. around the blooms. base. als may germinate in the spring instead of of environments. Cultivation breaks up roots, Most of these thistles have a par- The rest of the plant How it spreads. fall and act as biennials. Soil disturbance which can form new plants and subsequent is covered with short, Seeds often are blown ticular niche in the environment that and availability of moisture and sunlight colonies. cottonlike hairs that a long distance by they exploit to their advantage and Distribution. Prefers deeper, richer soils usually are the determining factors. give the foliage a wind. than many thistles. Canada thistle occurs in at the expense of other vegetation. In For assistance in identifying or con- characteristic grayish- The problem. every county in Oregon. North America, they don’t have the trolling these or other noxious weeds, green appearance. Bull thistle has been present in Oregon since great complex of insects and diseases Leaves sometimes extend down the stem, giving before 1900. It occurs along roadsides, in waste contact: areas, meadows, and forest clearcuts. It can form that evolved with them overseas. Free • Oregon Department of Agriculture, a “winged” or flattened appearance. How it spreads. Rapidly by seeds, as many dense stands in pastures that are in poor condi- from such pests, they are much more Noxious Weed Control Program tion. Promoting the health and vigor of grasses competitive in this country than in as 150,000 from a single large plant. 635 Capitol St. N.E., Salem, OR 97301 The problem. Yellow starthistle grows in a and forage through fertilization and rotational their native range. Phone: 503-986-4621 wide range of environments. It favors dry range grazing can make pastures much less susceptible Oregon is extremely vulnerable and pastures, where its sharp spines discour- to bull thistle invasion. Web: oregon.gov/ODA/PLANT/WEEDS Distribution. Bull thistle occurs in every to further invasion by thistles. Sev- age livestock grazing. Feeding on this plant can © 2006 Oregon State University • Your local Oregon State University county in Oregon. eral thistles are so well established Extension Service office cause susceptible horses to develop a nervous This publication was produced and distributed in furtherance in particular areas that eradication is system disorder called “chewing disease,” which of the Acts of Congress of May 8 and June 30, 1914. Extension • Your county weed program supervisor usually results in death because the horse is work is a cooperative program of Oregon State University, the not possible. However, much suitable unable to eat or drink. U.S. Department of Agriculture, and Oregon counties. habitat in Oregon is open to invasion Report new suspect invasions by Distribution. Major infestations occur in Oregon State University Extension Service offers educational and needs to be protected. Jackson, Josephine, Douglas, Baker, and Wheeler programs, activities, and materials without discrimination based calling the Invasive Species Hotline: on age, color, disability, gender identity or expression, marital counties, with sizable infestations present in Thistle identification is key to plan- 1-866-INVADER. status, national origin, race, religion, sex, sexual orientation, or ning and implementing an effective Umatilla County. Smaller infestations occur in veteran’s status. Oregon State University Extension Service is an Wasco, Sherman, Morrow, and Gilliam counties. Equal Opportunity Employer. Major infestations also occur in California. Published March 1989. Revised December 2006. PROBLEM THISTLES OF OREGON

Italian thistle Milk thistle Purple where they displace valuable forage species. The Distaff thistle Musk thistle sharp spines also deter animals and people and Carduus Silybum marianum starthistle can cause problems in recreational areas. Carthamus Carduus pycnocephalus Life cycle. Winter Centaurea Distribution. The only documented site of lanatus nutans annual or sometimes calcitrapa purple and Iberian starthistle in Oregon is in Life cycle. Winter Life cycle. Slenderflower biennial. Clackamas County and is under intensive man- annual or sometimes Biennial. Flowers. Red to agement. Small infestations in Sherman and Jack- biennial. Flowers. thistle Iberian 1 purple (occasionally son counties are believed to have been eradicated. Flowers. Yellow, Purple, 1 ⁄2 to 1 Carduus white), 1 ⁄2 to 3 inches starthistle Infestations in northern California continue to 1 to 2 inches in diam- 3 inches in diam- tenuiflorus in diameter. Single Centaurea iberica threaten Oregon. eter, at the end of eter, one per stem, Life cycle. Winter blooms are surrounded Life cycle. Bien- each branch. Blooms and usually nod- annual or sometimes by inch-long spines at nial. Also can act as late June through ding. Blooms June biennial. the top of each branch. an annual or short- Scotch thistle September. through August. Flowers. Purple, Blooms April to June, lived perennial. Seeds Onopordum Description. Dis- Description. 1 dying by July. numerous, ⁄2 to germinate in both acanthium taff thistle germinates Forms a spiny 3 Description. Milk ⁄4 inch in diameter, spring and fall. At a Life cycle. Biennial. in the fall to form rosette the first usually clustered thistle germinates in the control site in Clacka- Flowers. Red to rosettes with dark year and upright at the ends of the fall; during the winter it mas County, Oregon, purple, numerous, green leaves. In the stems, usually 3 to branches. The earli- produces rosettes up to it has been behaving as 1 to 2 inches in diam- spring, the stem 6 feet tall, in the est flowering thistle, 5 feet in diameter. The an annual, germinating eter. Short spines are emerges from the second year. Spiny it blooms from April leaves are shiny green in the fall and/or spring on the tips of each rosette to form a wings are formed through June, dying with distinct white mar- and setting flower dur- bract at the base of the rigid, spiny plant on stems by a con- by July. bling along the veins. ing the course of the head. Blooms mid-July covered with hairs on tinuation down the Description. Two Mature plants grow 7 to season. through August. stems and especially stem of the prickly similar species, grow- 10 feet tall. Flowers. Numerous, Description. The on flowers, giving a leaf base. 3 ing from 1 to 6 feet How it spreads. ⁄4 to 1 inch long. plant forms a rosette woolly appearance. How it spreads. By seeds. tall at maturity. Ital- Rapidly by seeds. Flower color varies the first year and a Stems reach a height The problem. Musk thistle is an aggres- ian thistle has white spots on the leaves and The problem. Milk from lavender to deep single main stem up of 2 to 4 feet. Stems sive plant that spreads rapidly to form dense fewer blooms per cluster than slenderflower thistle infests roadsides, purple. Marginal flow- to 12 feet tall in the are unbranched on stands, often displacing desirable plants. thistle. Leaves are deeply lobed, often woolly waste areas, and graz- ers are not enlarged. The bracts of the flower second year. The stems the lower one-third It infests pasture, range, and timber lands on the underside; the leaf margin continues ing lands. It commonly head are tipped with a stout, rigid, straw-colored have broad, spiny of the plant and very as well as roadsides, waste areas, and ditch down the stem to form winged stems. occurs in association with Italian thistle in hillside spine about 1 inch long with one to three pairs wings. The leaves have branched on the banks. How they spread. Rapidly by seeds, pastures. Once established, it spreads rapidly. Indi- of lateral prickles near its base. Blooms June sharp, yellow spines on upper two-thirds. Distribution. Sizable infestations occur which remain viable in the soil for as long as vidual plants are so large that forage displacement through September. the edges. How it spreads. By seeds. in Klamath, Lake, Malheur, and Umatilla 7 years. is high; in dense stands, livestock can be excluded Description. Purple and Iberian starthistle How it spreads. By The problem. Distaff thistle is adapted to a counties. The problem. These thistles are extremely entirely. are very similar in appearance. The seeds are the seeds. wide variety of range and pasture conditions. Its competitive in a hillside pasture environ- Distribution. Douglas, Coos, and Curry coun- distinguishing feature; purple starthistle seeds The problem. rigid and spiny nature can exclude livestock or ties have extensive infestations. Scattered smaller ment. In spring, they form dense stands, are plumeless, while those of Iberian starthistle Scotch thistle is com- wildlife foraging even after the plants mature and This publication was made possible through a grant infestations are found in Jackson County and the which severely limit grazing and restrict are plumed. Rosettes of the plant are deeply petitive with desirable die. from the USDA Forest Service–Cooperative Programs, a sighting and gathering of sheep and cattle. Willamette Valley. lobed with light-colored midribs. Light straw- plants and forms dense Oregon is attempting to contain and control all key partner in assisting landowners improve their forest They also infest roadsides, natural clearings, colored spines develop in the center of the stands that limit graz- infestations of distaff thistle. If you see this plant, resources. The USDA is an equal opportunity provider and clearcuts, industrial sites, and waste areas. rosette. Mature plants are from 1 to 4 feet tall ing by livestock. It’s common along roadsides, in take a small sample in a sealed container to your employer. Distribution. Major infestations occur in with a stout taproot. waste areas, and on rangeland. local weed control representative or Extension Financial support also was provided by the Oregon Douglas County and to a lesser extent in Coos How it spreads. Rapidly by seeds. Distribution. Extensive infestations occur in agent for identification. Department of Forestry and the Coos Soil and Water and Curry counties. Linn, Lane, Yamhill, and The problem. Purple and Iberian starthistle Malheur County. It also is common in Gilliam, Distribution. First detected in Oregon in Conservation District. Marion counties have limited infestations. seem to have the ability to adapt to a variety of Umatilla, Grant, Morrow, and Klamath counties. 1987, distaff thistle is established in a few areas Prepared by Ken French, IWM specialist, Oregon Depart- climatic conditions. They are extremely competi- Scattered small infestations occur in Douglas, in Douglas County and on one site each in Curry ment of Agriculture, Noxious Weed Control Program; tive along roadsides and in low-rainfall range Jackson, Jefferson, and Wasco counties. and Josephine counties. Major infestations occur Larry C. Burrill, Extension weed specialist emeritus, situations as well as in higher rainfall pastures, in California. Oregon State University; and Tim V. Butler, field opera- tions manager, Oregon Department of Agriculture, Noxious Weed Control Program. PROBLEM THISTLES OF OREGON