Noxious Weed Identification

Top five noxious weeds in Castle Rock

Several types of noxious weeds have been identified as the most undesirable, unwanted or priority for control in Douglas County.

Dalmatian Toadflax

  • List B – to be eliminated or suppressed depending on the infestation
  • Native to the Mediterrean area introduces as ornamental plant
  • Tall (3ft) plant that reproduces by seed and creeping underground roots
  • One plant can produce 500,000 seeds but does not spread far
  • Control best accomplished by early detection and eradication or multiple management strategies

Dalmatioan Toadflax
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Diffuse Knapweed

  • List B – to be eliminated or suppressed depending on the infestation
  • Native to the Mediterranean area
  • Tends to invade disturbed or overgrazed areas and roadsides
  • One plant can produce 18,000 seeds that may remain dormant for years but still be viable
  • Also known to outcompete native plants by releasing a chemical in the soil that suppresses other plant growth

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Leafy Spurge

  • List B – to be eliminated or suppressed depending on the infestation
  • Native to central and southern Europe
  • Long-living creeping perennial that spreads by seed but also has extensive root system that makes control difficult
  • A management scheme that combines control methods over four to five years is recommended

Leafy Spurge
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Musk Thistle

  • List B – to be eliminated or suppressed depending on the infestation
  • Spreads only by seed but one plant can produce up to 20,000 seeds
  • Prefers open degraded habitat and pastures
  • Can grow up to 6 feet tall

Musk Thistle
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Myrtle Spurge

  • List A – must be eradicated on all property
  • also called "donkey tail" or "creeping spurge"
  • drought-tolerant perennial native to Eurasia, first introduced to North America as an ornamental
  • considered a noxious weed because it is aggressive and proliferates easily, outcompetes native plants, and has toxic milky sap

Replacements for Myrtle Spurge

  • Colorado Four o'clock (Mirabilis multiflora)
  • Sulphur-flower Buckwheat (Eriogonum umbellatum)
  • Kinnikinnick (Arctostaphylos uva-ursi)
  • Creeping Barberry (Mahonia repens)
  • Four-nerve Daisy (Tetraneuris acaulis)
  • Tufted Evening Primrose (Oenothera caespitosa)

Myrtle Spurge
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