Noxious Weeds

What is a noxious weed?

All noxious weeds are non-native species. The Colorado Noxious Weed Advisory Committee considers a weed to be noxious if it meets one or more of the following criteria:

  • Aggressively invades or is detrimental to economic crops or native plant communities.
  • Is poisonous to livestock.
  • Is a carrier of detrimental insects, diseases or parasites.
  • The direct or indirect effect of the presence of this plant is detrimental environmentally  to natural or agricultural ecosystems.

All noxious weeds are invasive due to the lack of natural insects and disease to keep their populations in check.

Noxious Weed Species Information
Leafy Spurge

Can cause severe irritation of the mouth and digestive tract in cattle which may cause death.

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Canada Thistle

A colony forming perennial from deep and extensive horizontal roots. Difficult to control; breaking up roots by plowing only increases the number of plants.

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Common Mullein

A tall plant with big hairy leaves and a stalk of yellow flowers. One plant can produce over 100,000 seeds.

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Dalmatian Toadflax

Can easily crowd out desired forage.

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Diffuse Knapweed

Threatens pastures and rangelands.

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Downy Brome (Cheatgrass)

A difficult hardy winter annual to control.

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Field Bindweed

Difficult to eradicate because of the long, deep taproot which can penetrate the soil to a depth of 10 feet and which gives rise to numerous long lateral roots.

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Musk Thistle

Invades pasture, range and forest lands along with roadsides, waste areas, ditch banks, stream banks and grain fields.

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Is also called ‘Goathead”. It is a ground cover annual that punctures bike tires, and sticks into anything that steps on the dried sharp seeds.

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Purple Loosestrife

Infestations can impede water flow and reduce habitat for wildlife.

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Redstem Filaree

Purple flowered annual that covers the ground and does not let any other plants grow around them.

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Russian Knapweed

Widely established in the western US.

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Spotted Knapweed

Western states are experiencing a reduction in desirable plant communities as this species is allowed to spread.

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Yellow Toadflax

This creeping perennial is an aggressive invader of rangelands, displacing desirable grasses.

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