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.