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Knapweeds Growth Habit Leaves Root System Flower Bracts Taken from PNW432 Bighead Centaurea macrocephala Upright, stems unbranched; perennial Light-green, broadly lance- shaped with toothed edges and pointed tips Woody Taproot Solitary, in a large globe- shaped head; yellow Thin & papery, with fringed margins Black Centaurea nigra Upright, stems are few and branch near the middle; perennial from a woody root crown Green-gray, broadly lance- shaped basal leaves on a stalk Woody Taproot Rose to lavender Covered with “comb-like”, dark brown or black fringed margins up to 3x as long as the bract Bighead Black Diffuse Centaurea diffusa Upright, stems branch profusely; annual or short-lived perennial Slivery-green; lower leaves are divided, upper leaves are narrow and elliptical Taproot White, rose, or purple Covered with “comb-like” spines Meadow Centaurea jacea x nigra Upright; perennial growing from a woody root crown Deep-green leaves are lance-shaped & stalkless; basal leaves taper at both ends, upper are leaves smaller and not lobed Woody to fleshy Taproot Solitary, globe- shaped heads; rose to purple Fringes gold to dark brown, about the width of the bract and rounded at the tip Russian Acroptilon repens Upright; hardy, long- lived, perennial spreading by creeping roots and seeds Slivery-green; lower leaves long and lobed, upper leaves smaller & toothed. Horizontal, brown to black in color Diffuse Meadow Pink to purple Pearly and papery, with no noticeable fringes or spines Spotted Centaurea stoebe Upright; biennial or short-lived perennial; rosette will form in the first year followed by stocks in the second Medium-green with a silvery- gray cast; deeply lobed on young plants becoming elliptical with maturity Stout Taproot Solitary; purple, pink or sometimes white Fringed tips dark & short Brown Centaurea jacea Upright, stems branch near the top; perennial Lance-shaped, undivided; leaves grow progressively smaller near the top Woody Taproot Russian Spotted Rose to purple Tips are wider than base and the thin, papery margins have a dark brown center Yellow Starthistle Centaurea solstitialis Upright, stems branch and are ridged; winter annual forming a rosette early & then growing upright. Grayish-green; lower leaves are deeply lobed, upper leaves are smaller and pointed Taproot Single, terminal; bright yellow Modified into stiff spines up to ¾” long Brown Yellow starthistle ---PAGE BREAK--- FOR MORE INFORMATION ON WEEDS IN WASHINGTON, CONTACT: Washington State Noxious Weed Control Board P.O. Box 42560, Olympia, WA 98504 (360) 725-5764 Web site: http://www.nwcb.wa.gov Or Washington State Department of Agriculture 21 North First Avenue #103 Yakima, WA 98902 (509) 225-2604 Or Your local County Noxious Weed Control Board: You Can Help Protect Washington’s Environment from Noxious Weeds! Cover artwork by Laurel Baldwin Knapweed artwork taken from PNW 432 Produced by & Sue Winterowd, Coordinator of the Stevens County Noxious Weed Control Board First published in 2003 ¾ Overview Knapweeds are aggressive, invasive noxious weeds of pastures, cultivated fields, travel corridors, and any bare ground sites. They increase soil erosion, consume soil nutrients and crowd out native vegetation. Weed specialists have attributed the success of some knapweeds to their ability to release a natural herbicide that eliminates competition by killing neighboring plants. This enables these weeds to quickly and effectively take over an area once introduced. Knapweed infestations are noted to increase production costs for ranchers, impair the quality of wildlife habitat, decrease plant diversity, increase soil erosion rates, decrease the visual quality and appeal of recreational lands, and pose fire hazards. These species have little value as forage for cattle and game and some can cause chewing disease in horses. ¾ Dispersal Mechanisms Knapweed is easily moved by animals and birds that may pick up the weed seeds and disperse them. Wind and water can also move knapweed seeds, though the biggest contributors to the movement of weed seeds are humans. We transport them on our vehicles, on clothes, on recreational gear and equipment, and on farm and other heavy equipment. ¾ Management Timing is key for effective control of knapweeds, early detection and fast action can stop the weeds from becoming established in an area. Managing a knapweed problem should be done by using a combination of mechanical, chemical, cultural, biological controls. You should do a site specific evaluation to determine what control tactics will work the best for your land. For more information on control consult your county weed control board, county extension office, or the Pacific Northwest Weed Control Handbook. The best knapweed control is prevention! You must correctly identify the plant to keep an infestation from becoming established. SELECTED KNAPWEEDS OF WASHINGTON Information & Identification