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

Family: Asteraceae (Aster Family)

Synonym(s): Acroptilon repens, 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. br />
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.
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History: It has been declared a noxious weed in 18 US states and four Canadian provinces.

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: As it is allelopathic and survives under a variety of conditions, it has been become an invasive exotic wherever it is imported. Infestations reduce yields of desired plants and decrease the production quality of rangelands.

Horses with prolonged consumption of R. repens can develop 'chewing disease' or equine nigropallidal encephalomalacia (ENE); a permanent disease caused by lesions in the brain. Symptoms include the inability to eat or drink, aimless or awkward movement, and spontaneous activity. Symptoms may occur after ingestion of 60-200% of its body weight for at least 30 days. However, R. repens is not toxic to sheep and cattle have grazed infested pastures with no evidence of toxicity

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: Temperate Asia and Europe

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: 2024-02-08 by ARMO, TISI