Russian KnapweedAsteraceae or Sunflower Family
Centaurea repens

IDENTIFICATION:
GROWTH HABIT: Perennial forb, grows up to 3 feet tall.
LEAVES: Entire or serrate, narrow to a sessile base. Basal leaves are toothed and covered with fine hairs, making them appear grayish-green in color.
STEMS: Erect, openly branched. Stems are covered with fine, white hairs that give the stem a blue-green color.
FLOWERS: Cone-shaped flowering heads are 1/4 to 1/2 inch in diameter, solitary at the tip of leafy branchlets. Flowers are pink to lavender with many pearly involucral bracts with rounded or acute papery margins. Individual plants produce as many as 200 flower heads. Flowering occurs from June to September.
Russian Knapweed RosetteROOTS: Grow 6-8 feet in the first season and 16-23 feet in the second season.
SEEDS: A single plant may produce 1,200 seeds, which remain viable for 2-3 years.
REPRODUCES: Primarily by adventitious shoots from widely spreading black roots and also by seed.
HABITAT: Cultivated fields, orchards, pastures, and roadsides.

"This weed is toxic to horses causing a neurological disorder"

MANAGEMENT OPTIONS:

Hand pulling:  Handpulling is not an effective tool for the management of Russian knapweed as it will rapidly re-sprout from rhizomes.
Mowing:  While Russian knapweed does spread by seed, it mostly spreads by rhizomes through the soil.  Mowing will reduce biomass, but it is not an effective method of control for this species.
Biological control: N/A
Grazing:  Grazing is not an effective tool for the management of Russian knapweed due to its deep, rhizomatous root system and can actually cause a neurological disorder called “chewing disease” in horses.
Herbicide:  There are a number of herbicides that provide effective control of Russian knapweed. The following herbicides are recommended for control of Russian knapweed.  Always consult product labels and read them carefully to ensure correct species/land management usage and chemical application.

Trade Name: Active Ingredient: Rate: Efficacy: Comments
 Tordon 22k Picloram 1 quart /acre  Effective if used during bud stage, while in flower, or in the fall. Cannot be used near wells, surface water, or shallow ground water.
 Milestone Aminopyralid 4-6 oz/acre  Effective when used between bolt and bud stage, or in the fall.  Can be applied to waters edge; cannot be used in landscaped areas and current or future vegetable gardens.

 

 

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