Impacts of Invasive Thistles Invasive Thistle Management THISTLES OF THE • Invasive thistles commonly invade Prevention: Thistles are shade intolerant disturbed areas: pasture land, waste and prefer disturbed areas. Cultivate ILLAMETTE areas, roadsides, agricultural land, native plants and use careful grazing W riparian areas, forest openings, etc. practices to minimize disturbance. VALLEY • They can spread rapidly. Biological Control: Introduced species that attack invasive thistles are present in • Lack of control can result in the Willamette Valley. R. conicus and L. Native or reductions in crop production of up to planus attack native thistles. Contact the 25% in infested areas. OR Dept. Agriculture for more info. Non-Native Invasive? • Invasive thistles take the place of Chemical Control: Herbicides can be other forbs and native grasses and used to control the growth and spread of most are not palatable to livestock; in invasive thistles. Contact your local large amounts, slenderflower thistle agricultural extension agent or soil and water conservation district office for can be toxic to sheep and cattle. specific treatments. • Invasive thistles eventually form dense Bull Thistle monocultures which decrease Hand pull or cut 1 inch below soil surface biodiversity. These monocultures do before flowering. Tilling, as well as goat not provide habitat for most wildlife, and sheep grazing, are also effective. including many game animals. Slenderflower & Italian Thistle Mowing is not effective. Hand pull/dig at seedling stage. For larger infestations, till Why are our Native Thistles deeply before flowering occurs. Canada Thistle Important? native Cirsium edule Mow or hand pull every 3-4 weeks for • Native thistles provide food for insects entire growing season. that also eat invasive thistles. How do you identify among native • Native bees and butterflies are great C. brevistylum photos courtesy of Toby Query. pollinators and a valuable agricultural Cover photo Dominic Maze. All other photos and non-native thistles? courtesy of Gerald D. Carr. For more information asset. Our declining populations of contact Dominic Maze: How do non-native, invasive native thistles provide excellent habitat [email protected] or for these pollinators without [email protected] thistles harm the environment? www.portlandonline.com/bes/invasives threatening agricultural systems. This brochure was made possible by the Western Why are native thistles important? • Native thistles were used by the Invasives Network, the City of Portland Bureau of Environmental Services, and the efforts Dr. Calapooia and Chinook peoples and are Catherine De Rivera’s students at Portland State How do you manage non-native, a part of our cultural heritage. University. May be reproduced for non-commercial purposes and without written consent. 2013. invasive thistles? WILLAMETTE VALLEY Few Leaved Thistle (Cirsium remotifolium Canada Thistle (Cirsium arvense) var. odontolepis & var. remotifolium) • General: 0.5-2 m NATIVE THISTLES tall, perennial, • General: 0.3- 1.8 m tall, deep creeping root taprooted, short-lived system that forms Indian Thistle, Clustered Thistle, Short perennial, weakly erect aggressive colonies Styled Thistle (Cirsium brevistylum) stems, sparingly branched, wooly or • Leaves: generally becoming hairless lobed, wooly • Leaves: wooly beneath, beneath, rufed becoming hairless above, margins with very deeply lobed or divided, sharp yellowish spiny, lower leaves have prickles or entire, spiny petioles (leaf lower leaves with stems), upper leaves narrow bases General: 0.5-2.5 m tall, • lack petioles • Flowers: small taprooted biennial or • Flowers: several (less than 2 cm), clustered, purple blooms, short-lived perennial, clustered creamy white unisexual (composed of male or female flowers), wooly below flowerhead, to purple flowerheads, male flowers shorter (1.25-1.5 cm) than female rarely branched bell-shaped, many flowers (2.25-2.5 cm), leaves below flowerhead • Leaves & stems: coarsely toothed with weak spines, narrow spiny-tipped less than 2cm long thin, wooly below and green above. Stems soft. leaves below flowers • Flowers: red-purple (rarely white), slender Italian Thistle (Carduus pycnocephalus) and flowerhead base, dense bristles, style (small, WILLAMETTE VALLEY NON- white stalks) exerted out flower tubes 1-2 mm Slenderflower Thistle (Carduus NATIVE, INVASIVE THISTLES tenuiflorus) Edible Thistle (Cirsium edule) • General: 0.4-3 m tall biennial/perennial with Bull Thistle (Cirsium vulgare) • General: similar-looking taproot, simple stems. annuals, 0.3-1.8 m tall

• Leaves: deeply lobed, white spots on Italian, • Leaves: wooly below, • General: 0.3-2 m tall; becoming hairless biennial; stems are leafy, “wings” extend down above, deeply pinnately branched and wooly stem, wooly underside lobed, dense small • Leaves: narrow lobes; • Flowers: clustered, spines on the margins terminal lobe longer than pink-purple, 2.5 cm • Flowers: Few pink- laterals; tipped with across, blooms early purple (rarely white) yellowish spine-like prickles; wooly under-side; (Apr-June) dying by flowerheads, leaves conspicuous spiny “wings” extend down stem Aug. Italian has fewer below flowerhead are lobed, becoming simple and tipped with a spine, from leaves and covered with stif, blunt hairs blooms, and stif, style exceeds flowers by 0.25-0.75 cm • Flowers: large (2.5-5 cm), purple, many narrow forward pointing hairs leaves below flowerhead tipped with spines on flower leaves