Identification, Distribution,

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Identification, Distribution, Impacts of
Russian knapweed

• Mark Renz, PhD
• Extension Weed Specialist
• NMSU

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Adventitious buds sprouting on roots.
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Russian Knapweed

• Identification
• Lower Leaves are 2 to 4 inches long and deeply
  lobed.
• Upper leaves are smaller and less lobed with
  smooth margins.
• Flower heads occur on shoot tips, and are
  urn-shaped generally 1/4 to 1/2 inch in diameter
  with smooth papery bracts.
• Flower color can ranges from pink to lavender or
  white
• Roots are perennial, creeping, and have a
  distinct black scaly appearance.

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Rounded and papery bracts.
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Note Black and scaly deep penetrating roots.
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Plant habit

• Stems erect 1-2 ft in height
• Lower Leaves lobed
• Upper leaves are smaller and less
• lobed with smooth margins

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Impacts

• Extremely competitive plant
• As infestations develop they displace nearly all
  herbaceous resident vegetation
• Reduces forage for livestock
• Can nearly eliminate plant biodiversity
• Produce allelopathic chemicals that inhibit
  growth of other plants
• Compounds can hamper revegetation efforts
• Poisonous to horses
• Causes chewing disease, a neurological
  disorder that produces brain lesion and ulcers in
  the mouth
• Generally avoided by grazing animals due to
  bitter taste

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Distribution

• Native to southern Asia
• (Mongolia, Iran, Armenia, Turkestan)
• Introduced in infested alfalfa seeds 1890s
• Can find it in 412 counties in 21 western states
• First documented in 1943 in Quay County

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Russian Knapweed

• Shoot biology
• Root biology
• Reproductive biology
• Management options

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Shoot biology

• Shoots emerge in early spring from root buds
• Can form dense stands 100-300 shoots/m2
• Shoots densities as low as 11/m2 have
  significantly reduced yields in crops
• Infestations can persist for gt100 years
• Can survive in low light areas (under tree canopy
  in riparian areas)
• increased leaf area

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Root biology

• The main method of spread for Russian knapweed is
  from adventitious buds and the creeping perennial
  root system.
• Roots can grow 6 to 8 feet in one season, and
  expand radially up to 14 yd2 in two seasons.

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Seed biology

• Russian knapweed is not a prolific seed producer.
• Each shoot can produce 50 to 500 seeds
• Seeds remain viable in the soil for 2 to 3 years
  (Beck 2003).

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Russian Knapweed management

• Prevention, early detection and eradication are
  the best management tools, as large infestations
  are difficult to eliminate.
• Small establishing infestations require few
  resources to eradicate and typically resident
  plants recover from management methods
  eliminating the need to restore the site.
• The best management plan includes cultural
  control combined with mechanical and/or chemical
  control techniques.
• A single control strategy, such as mowing or
  herbicide use, is not sufficient to control old,
  dense infestations.

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Common management tools

• Mechanical
• Mowing, disking can have some success if
  integrate with other methods
• Biological
• CLASSICAL Subanguina picridis, Stem/leaf gall
  nematode. Several others being researched
• COMPETITION Healthy, competitive plant community
• Herbicides
• Can be effective and economical for large
  infestations
• Need to replace open space created

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Herbicide Active Ingredient Rate of Herbicide Timing of application Comments
Tordon 22K Picloram 1-2 qts/A Anytime plants are actively growing best results in the fall after frost Residual herbicide Selective, will not harm many grass species
Tordon 22K 2,4-D1 Picloram 2,4-D 11.5 qt/A 0.5 lbs ai/A Anytime plants are actively growing best results in the fall after frost Residual herbicide Selective, will not harm many grass species
Reclaim 2,4-D1 Clopyralid 2,4-D 1.0 pt/A 0.5 lbs ai/A Anytime plants are actively growing best results in the fall before frost Residual herbicide
Reclaim ( Transline) Clopyralid 0.67-1.33 pts/A Anytime plants are actively growing best results in the fall before frost Residual herbicide
Plateau methylated seed oil Imazapic methylated seed oil 12 fl oz/A 1 qt/A Late fall after frost Residual herbicide
Arsenal Imazapyr 2 pts/A Anytime plants are actively growing best results in the fall after frost Residual herbicide
Many compounds Glyphosate 3-4 qts/A Flowerbud stage Poor control can result some years
Escort Metsulfuron 0.75 1.0 oz/A Flowerbud stage Residual herbicide Selective, will not harm many grass species
Telar Chlorsulfuron 1.0 2.0 oz/A Flowerbud stage Residual herbicide Selective, will not harm many grass species