Invasive Plant Species of the Pacific Northwest

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Invasive Plant Species of the Pacific Northwest
By Kenneth Strawn
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Invasive Species

• Out compete native, desirable species
• Reduce biological diversity
• Reduce forage production of grazing lands
• Contaminate crops
• Invade all types of habitat, from wet marshes
  and pond banks, to dry, arid range areas, and
  forested locations

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Grazing / Biological Control of Invasive Plants
For some invasive species, grazing by livestock
is effective in controlling propagation
/.spread Integrated Pest Management- using
biological controls such as insects to destruct
invasive plants Combinations of these methods
have proven very effective for some invasive
plants, such as the leafy spurge shown below
Sentinel Butte, North Dakota
2000
1998
Ag Research Service, USDA
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Leafy Spurge (Euphorbia esula)

• Characteristics
• Erect, branching, perennial herb smooth stems
  contain milky,white sap
• 2.5-3 ft tall, yellow flowers develop in
  mid-June, deep root system, 7 year seed viability
• Thrives in dry range conditions also found in
  wetter pastures, fields, etc.
• Harmful Effects
• Displacement of native vegetation, steals
  nutrients, emits toxins into soil
• Quickly reduces forage plants- cattle refuse to
  graze w/ 10-20 spurge present (irritates
  digestion)
• Devalues land-Klamath Co. ranch worth 125-150
  per acre before spurge, 22/ acre after
  infestation
• Control MethodsBio- controls/ sheep grazing
  promising
• Sheep prefer spurge to other plants
• Flea beetles, stem/root borer, shoot tip gall
  midge

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Scotch Broom (Cystius scoparius)

• Characteristics
• Perennial evergreen shrub in legume family
• Stiff, angled dark green branches yellow
  flowers
• appear April-June
• Oval, dark seeds, 1/8 in long last to 60 years
  in soil
• Harmful Effects
• Interferes w/ establishment of conifer
  seedlings crowds out forbs, grasses, tress
• Reduces livestock feed where stands are allowed
  to gain control
• May be toxic to humans and animals
• Control Methods
• Over time, grazing by goats in young stands may
  be effective
• Mechanical removal works well cultivation
  prevents growth
• Chemical applications are limited and
  necessitate follow-up eradication efforts

Scotch Broom near Pedee, Oregon (Kenneth Strawn)
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Purple Loosestrife (Lythrum salicaria L)

• HistoryIntroduced to NE U.S. in 1800s for
  ornamental / medicinal use
• Characteristics
• Erect, perennial herb w/ square woody stem
• Grows in wet areas- meadows, marshes, stream
  banks, ponds, etc
• Lance shaped, stalkless leaves- rounded at base
• Grow 4-10 ft high, 30-50 stems from single
  rootstock
• Magenta colored flowers through summer
• Harmful Effects
• Out competes native grasses, sedges, other
  wildlife food sources
• Reduce waterfowl habitat
• Control Methods Biological control very
  promising in U.S.
• Root mining weevil and two leaf feeding beetles
  approved, others under investigation
• Manual pulling / chemical application may be
  effective in small stands

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English Ivy (Hedera helix L.)

• Native Area Europe, western Asia, northern
  Africa
• Characteristics
• Evergreen, climbing vine
• Attach to trees, buildings by root-like
  structures-produce sticky substance
• Leaves- dark, green, waxy- arranged alternately
  along the stem
• Black fruits appear in spring- enclose hard seeds
• Grows from cuttings or seeds spread by birds
• Harmful Effects
• Shades out forest vegetation, including trees
• Aids in proliferation of bacterial leaf scorch-
  harmful to elms, oaks, maples
• Control Methods
• Manual pulling from ground / trees variety of
  chemical applications
• No known biological controls

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Spotted Knapweed (Centaurea bierbersteinii D.C.)

• History
• Arrived in North America as contaminant in
  
  alfalfa/clover seed and in ship ballast
• Characteristics
• biennial member of sunflower family, stout tap
  root
• 8-50 inch flowering stems rosette leaves 8 in
  long, 2 in wide alternating leaves
• Thrives at wide variety of elevations and
  precipitation amounts open coniferous forests,
  certain prairie habitats, and disturbed areas.
  Establishes with difficulty in thick grass
• Harmful Effects
• outcompetes natives, decreases diversity,
  reduces forage production
• increases soil erosion, creating stream
  sedimentation

• Control Methods Prevention is key-clean
  equipment, feed weed free hay, etc
• Bio-controls 3 moth species, weevil,
  2 seed flies know to be effective
• Long term grazing and manual removal
  feasible in some cases

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Sources of More Information
Oregon Department of Agriculture, Plant
Division Noxious Weed Control Program, 503
-986-4621 Invasive Species Hotline,
1-866-INVADER   Agricultural Research Service,
USDA www.ars.usda.gov National Invasive Species
Council www.invasivespecies.gov