Community Ag Alliance: The cost of noxious weeds

Greg Brown/For the Steamboat Today

Native wild land vegetation, managed forest and rangeland and agricultural land are threatened by noxious weeds, which can reduce or eliminate wildlife habitat, pollinator food sources and grazing resources.

Native plants occupy specific niches in the ecosystem to utilize the climatic, soil, geographic and moisture resources to flourish and maintain their populations. They share these resources with other organisms suited to the environment, and while there may be competition for resources, a system of checks and balances exists which keeps thing roughly stable and manageable. When a non-native plant with aggressive reproductive capabilities is introduced into this relatively stable system, it is usually the native plants that suffer, because the alien species may not have any natural deterrent to exploiting the resource base.

By definition, noxious weeds in Colorado are always non-native plants, usually with a Eurasian source. They have been imported into North America as contaminants in agricultural seed, e.g. houndstongue; ornamental escapes, e.g. dalmatian and yellow toadflaxes; or as contaminants in packing and shipping materials, e.g. cheatgrass. When native plants are displaced, there is often a significant decrease in plant diversity and corresponding declines in the capacity for the community to support native fauna and livestock. Rangeland forage can be seriously impacted for grazing, and the resultant economic losses to rural communities can be substantial. Leafy spurge can readily reach cover densities of 50 percent, with a corresponding carrying capacity reduction of 90 percent for cattle.

Noxious weeds can also alter the environment to make it even more favorable for their success. They may exude chemical compounds from their roots which inhibit the growth of other plants (allelopathy), and their optimum season of growth can be different than the natives they are impacting. Cheatgrass begins growth very early in the spring and provides some grazing. However, it reaches maturity very quickly, dries up and becomes a fire hazard, which increases fire frequency, often to the detriment of native species. Some species, such as tamarisk, accumulate salt, which changes the soil chemistry to the point where other species will not germinate.

It is estimated more than 100 million acres in the U.S. are infested with noxious weeds, resulting in an economic loss of $6 to $18 billion per year and growing approximately 8 percent annually. These losses represent direct costs for treating the weeds and indirect costs associated with agricultural losses and habitat impacts. Pollinators native to an environment have been found to make substantially less use of invasive plants than of native flora, and the displacement of pollinators may result in reduced pollination of the native species, which further erodes populations.

It is these impacts on native landscapes and agricultural lands that have led to the establishment of weed laws across the country. The Colorado Noxious Weed Act applies to all state, federal and private land in Colorado and requires every landowner and manager to control noxious weeds. For details on specific weeds and recommended control strategies, please contact Greg Brown, Routt County Weed Program, at 970-870-5246 or or Todd Hagenbuch, CSU/Routt Extension, at 970-879-0825 or

Greg Brown is weed supervisor for the Routt County Weed Program.

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