Norman E. Rees, USDA Agricultural Research Service, Bugwood.org

Family: Asteraceae (Aster Family)

Synonym(s): Centaurea picris

Duration: Perennial

Habit: Herb

Listed by:
Invasive Plant Atlas of the US: 1
Federal Noxious Weed: 0
TDA Noxious Weed: 0
TPWD Prohibited Exotic Species: 0

Description: Noxious perennial to 1 meter tall, with dark, creeping rhizomes. Plants exhibit allelopathic effects and are aggressively competitive, facilitating rapid colonization and development of dense stands. Infestations can be extremely long-lived due to extensive root and rhizome systems. Stems dieback after flowering in summer, and new shoots are generated in spring. Introduced from Central Asia. Like yellow starthistle (Centaurea solstitialis L.], Russian knapweed is toxic to horses, causing nigropallidal encephalomalacia or "chewing disease" when sufficient quantities are consumed. Under most circumstances livestock will avoid grazing Russian knapweed because of its bitter taste.

Other white, pink, and purple-flowered knapweeds in the genus Centaurea and bearded creeper (Crupina vulgaris Cass.) are most easily distinguished by their lack of dark, spreading rhizomes and by phyllary and achene characteristics. In addition, only bearded creeper has leaf margins with stiff hairs barbed at the tips (glochidiate hairs) and flower receptacles with flattened, scale-like, chaffy bracts.

History:

Biology & Spread: Reproduces primarily by vegetative shoots from rhizomes. Plants usually produce small quantities of viable seed. Seed heads mostly remain closed. Seeds disperse passively near the parent plant or with the seed head. Seeds germinate over a broad temperature range (0.5-35 C; optimal 20-30 C), and light is not required. Scarification, fluctuating temperatures, and alternating light and dark periods increase germination. Seed can remain viable about 2-3 years.

Ecological Threat:

US Habitat: Fields, cultivated sites, orchards, vineyards, roadsides, ditchbanks, and waste places. Inhabits many soil types.

Distribution

US Nativity: Introduced to U.S.

Native Origin: Temp. Asia, Europe (Germplasm Resources Information Network)

US States: AR, AZ, CA, CO, IA, ID, IL, IN, KS, KY, MI, MN, MO, MT, ND, NE, NM, NV, OH, OK, OR, SD, TX, UT, WA, WI, WY

Resembles/Alternatives:

Management: When irrigation is possible, Russian knapweed may be effectively managed with a combination of herbicides and crops that provide dense shade. It is extremely difficult to establish perennial grasses in dense stands of Russian knapweed due to allelopathic chemicals produced by the knapweed. Use of herbicides followed by reseeding of perennial grasses has resulted in increases in grass cover by >50%. Reseeding of perennial grasses in combination with the knapweed gall nematode has not been examined. Long term control will inevitably require yearly examinations of infestations and subsequent management for success.

USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.

Listing Source

Texas Department ofAgriculture Noxious Plant List
Texas Parks and Wildlife Department Prohibited Exotic Species
Invaders Program
Federal Noxious Weed
Union of Concerned Scientists
United States Forest Service Southern Research Station

Text References

Data Source

Encycloweedia, California Department of Food and Agriculture.
Know Your Knapweeds

Last Updated: 2019-08-30 by DEW(LBJWC); update: HFL (LBJWC)