spotted knapweed
Spotted Knapweed
CEMArosette

Asteraceae or Sunflower Family
Centaurea stoebe (syn. maculosa)

IDENTIFICATION:
Growth Habit:
Biennial or short lived perennial, grows 1-3 feet tall.
Leaves: Long and divided on lower, short and narrow above, covered with fine hairs.
Stems: Erect with slender wiry branches, covered with fine hairs.
Flowers: On branched stem tips flowers are pink to purple, rarely white. The seed head has black tipped bracts.
Roots: Taproot, and well developed, fibrous.
Seeds: Produces 1,000 seeds per plant, viable up to 9 years.
Reproduction:
By seed.
Habitat: Found in meadows, roadsides, native grasslands, pastures, and waste places.

MANAGEMENT OPTIONS:
Handpulling: This is an extremely effective method on small-scale infestations of spotted knapweed. Pulling is easiest when soil is moist; allowing you to remove most of the taproot and kill the plant. Any stage from flowering on should be bagged and removed from the site in order to minimize seed at the site.
Mowing: Mowing will help reduce seed production of spotted knapweed; however, repeated mowing will result in plants flowering and setting seed below the blades of the mower. Mowing should occur during the bud stage but before flower to prevent cut plants from producing viable seed.
Biological Control: There are thirteen biological control agents that have been released in Montana to control spotted and diffuse knapweed. Of those species, eight have been shown to effect the health of knapweed populations. The majority of these species are widespread in Western Montana. Contact the Missoula County Weed District for assistance with monitoring and additional releases.
Grazing: Repeated grazing by cattle, sheep and goats can be effective at reducing levels of spotted knapweed if managed to reduce damage to desirable species such as native forbs and grasses. Grazing should occur when native species are dormant (either in the spring before native species begin growing or in the fall after they have dropped their seed). Managers should also be careful not to graze so much as to produce excessive bareground, which can result in increased weed invasions.
Herbicide: The following herbicides have been labelled for controlling spotted 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 pt/acre most effective in actively growing plants; spring or fall  Cannot use near surface water, shallow water, landscaped areas and current or future vegetable gardens 
(Restricted Herbicide - need an applicator license to use.)
 Milestone  aminopyralid  4-7 oz/acre most effective in actively growing plants; spring or fall   Can be applied to waters edge;
cannot be used in landscaped areas and current or future vegetable gardens,
mulch or manure from treated areas should not be applied to vegetable gardens or composted for vegetable gardens  
 Forefront  aminopyralid + 2,4-D  2 pts/acre most effective in actively growing plants; spring or fall   Can be applied to waters edge; 
cannot be used in landscaped areas and current or future vegetable gardens, 
mulch or manure from treated areas should not be applied to vegetable gardens or composted for vegetable gardens  
 Curtail  clopyralid + 2,4-D  2 qts/acre most effective in rosette to bud stage 
 2,4-D  2,4-D  2 qts/acre least effective herbicide listed
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