Colorado Noxious Weeds

Aliens have invaded the Colorado landscape! These aliens are in the form of non-native weeds called "noxious" in Colorado. They've gotten that name because of their invasiveness, aggressiveness and the rate in which they spread. Noxious weeds are difficult to control, and most are very adaptable. They also can withstand a variety of harsh conditions, including climate extremes, drought and poor soils.

There are approximately 1 million acres of noxious weeds in Colorado. The weeds cost Colorado residents more than $10 million annually in lost productivity. Noxious weeds often displace native plants. Many native species have been forced out of their natural habitat.


There are several noxious weeds in Colorado. Among the worst are leafy spurge, spotted knapweed, diffuse knapweed, Russian knapweed, Canada thistle, musk thistle, Dalmatian toadflax, yellow toadflax, field bindweed and purple loosestrife.


Weed management includes cultural practices such as avoiding overgrazing, re-vegetating disturbed soils and maintaining the vigor of desirable grasses or other plants that compete with weeds. The easiest time to control noxious weeds is when only a few plants are present. Mowing weeds before their seeds are mature will help prevent the seeds from spreading and will reduce weed vigor.

Biological control can involve using livestock such as sheep and goats to graze on weeds, which reduces their vigor. It also may involve introducing a specific disease or insect to affect weeds. Biological control has proven to be effective to varying degrees on some weeds.


Herbicides may be used on noxious weeds as part of an integrated control strategy, often in combination with cultural and biological controls.


For more information, see the following Colorado State Extension fact sheet(s).

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