The Huerfano County Noxious Weed Office is here to help landowners address their noxious weed control related issues. Services include: control recommendations, vegetation management plan development, species I.D., equipment calibration training, release of biological control agents, chemical (herbicide) applicator safety training, and species distribution mapping.

We ask for the public’s assistance in combating the ever evolving threat that noxious plant species pose. It is the legal responsibility of all landowners\tenants to control the designated noxious plant species in accordance with the Colorado Noxious Weed Act of 1991 (C.R.S Title 35, Article 5.5).

35-5.5-104. Duty to manage noxious weeds. It is the duty of all persons to use integrated methods to manage noxious weeds if the same are likely to be materially damaging to the land of neighboring landowners.

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There are 79 plant species designated as noxious weeds in Colorado and an additional 19 that are being closely monitored to determine their potential to become problematic within our state. These are non-native species that take a devastating toll on our native ecosystems and agricultural lands. These non-native species displace our native\desirable species through aggressive plant competition. The deleterious effects of these noxious plant species include: habitat loss, reduced biodiversity, reduced crop yields, increased risk of wildfires, increased soil erosion, heavy water consumption, increased flooding and loss of recreational areas\opportunities. Within this guide readers will find the top 10 most problematic noxious plant species in Huerfano County along with basic identification and control information. While these species are problematic throughout our region, the 2018 Spring Fire burn scar is particularly vulnerable given the large scale site disturbance. These invasive plant species reproduce at a much greater pace than our native plant species and have the potential to greatly impact the recovery of our burn scars. The key to effective invasive vegetation management is early detection and rapid response. A successful rate of control is greatly reduced as infested acres increase.

This perennial species is particularly difficult to control due to its extensive underground root system that can spread up to 17 feet deep and 15 feet laterally. New plants develop from the root system at any depth and can also develop from root fragments. Leafy spurge also has a unique ability to spread seeds by its three chambered seed pod literally exploding, projecting seeds 15 feet or more. There are approximately 350 seeds produced per plant annually, with an overall seed viability of 5-8 years. Due to the extensive underground root system, control options are limited.

Distribution in Huerfano County: The heaviest concentrations of leafy spurge are located around the La Veta and Chama\Redwing areas. Leafy spurge is well adapted to many habitats\soil types and infests over 3 million acres in 29 states

This is another perennial species that spreads by an extensive root system and seed. Roots can spread up to 20 feet deep and 15 feet laterally. Each plant produces up to 5,000 seeds per plant with a seed viability of over 20 years. Canada thistle is regarded as one of the most problematic weeds, affecting a variety of land\soil types. Root fragments are capable of producing new plants. Due to the extensive underground root system, control options are limited.

Distribution in Huerfano County: Canada thistle is widespread throughout the county with the heaviest concentrations found among riparian areas and irrigated lands.

This perennial species shares many of the same characteristics as the aforementioned species, being that it has a root system that spreads 12-30 feet a year, spreads by its root fragment, and is capable of producing nearly 5,000 seeds per plant annually.   Hoary cress also secretes its own herbicide that precludes the growth of other vegetation, known as allelopathy. This has historically been a difficult species to control given that flowering takes place early in the season and the window of chemical susceptibility is relatively short. Control options are limited.  75% of its biomass is located in the root system.

Distribution in Huerfano County:  Hoary cress is widespread throughout Huerfano County with the heaviest concentrations found around areas that are irrigated or have a high water table.  Hoary cress is particularly problematic around the La Veta and Gardner areas among rangelands and hay fields.

This perennial species has an extensive and vigorous black, scaly root system. It is capable of out competing desirable vegetation by spreading from seed and root rhizome. This plant is very toxic to horses, affecting the nervous system similar to Parkinson ’s disease in humans. Facial muscles freeze; there is an inability to chew and drink, and an overall drooping of facial muscles. No treatment is available, euthanasia is recommended to prevent starvation. This plant also holds allelopathic properties (self generated herbicides that affect neighboring plants). This plant has reproduced to nearly epidemic proportions in the San Luis Valley, to the point that in some cases the expense of control measures are not economically feasible compared to land value\use.

Distribution in Huerfano County: Russian knapweed distribution is limited within Huerfano County when compared to neighboring areas. Documented populations exist around Old La Veta Pass, Little Sheep Mountain and C.R. 555 west of Gardner. Russian knapweed is widespread throughout the San Luis Valley.

This is a biennial species and sometimes short-lived perennial that unlike the previous plant descriptions, reproduces only by seed. Seeds are spread by dead plants breaking off in the winter months and becoming “tumbleweeds”. Diffuse knapweed is known as a pioneering species given its ability to quickly invade disturbed and undisturbed ground alike which precludes the growth of desirable plant species. This species has allelopathic properties and is capable of hybridizing with spotted knapweed.

Distribution in Huerfano County: Diffuse knapweed is found in limited areas within Huerfano County. The heaviest concentrations are located along county roads 351, 310, 320 and within Lathrop State Park.

This biennial species and sometimes short lived perennial reproduces only by seed. This species commonly forms dense monocultures that preclude the growth of desirable vegetation. Spotted knapweed has allelopathic properties and can produce up to 140,000 seeds per square meter. Plants can self pollinate and hybridize with diffuse knapweed.

Distribution in Huerfano County: The heaviest concentrations of spotted knapweed are located along Old La Veta Pass and the Hwy 160 corridor west of Tres Valles. These populations are anticipated to grow exponentially due to the site disturbances caused by the 2018 Spring Fire and limited access for treatments.

This biennial species is perhaps the most easily identifiable of all the thistles given its large physical profile. Plants are capable of growing up to 10 feet tall and produce 8,000-40,000 seeds per plant annually. Seed viability is over 20 years. While relatively easy to control compared to the species listed prior, it is one of the most widespread noxious weeds in Huerfano County, capable of forming dense monocultures that crowd out desirable vegetation, and blocking corridors of travel for livestock.

Distribution in Huerfano County: Scotch thistle is one of the most widespread and problematic species within the county. Plants can be found among a variety of sites, especially disturbed areas and rangelands. Plants can be found within the municipalities of Walsenburg and La Veta as well. Infestations become sparse above 9,000 feet in elevation. Scotch thistle can be found in varying growth stages year-round in Huerfano County.

This is a biennial species that reproduces only by seed. Each plant can produce up to 20,000 seeds with a seed life of 6-9 years. Plants grow up to 8 feet tall. Musk thistle is highly competitive and is well adapted to many habitats. Immature plants are often confused with Scotch thistle.

Distribution in Huerfano County: Musk thistle is most commonly found in the higher elevations of Huerfano County but can grow in most areas. While somewhat widespread, the largest infestations occur along the Apache Creek corridor, Medano Pass, Middle Creek and Sulphur Springs area.

This biennial species reproduces by seed. Each plant can produce over 2,000 seeds annually that are largely distributed by their ability to cling to animal fur and clothing, spreading them great distances. This species is widespread and nearly naturalized in Huerfano County. This plant contains toxic alkaloids that cause liver cells to stop reproducing. Animals may live six months or more after consuming a lethal dose. Horses and cattle are most prone to poisoning.

This perennial shrub\small tree is one of the most widespread and damaging noxious plant species in Huerfano County. Tamarisk invades our native riparian ecosystems with devastating results. Nearly all river and stream corridors below 7,200 feet in elevation are heavily infested in our area. Tamarisk precludes the growth of native plant species by growing in thick monocultures that not only creates intensive plant competition, but also by its ability to manipulate soil chemistry. Tamarisk roots reach deep into the soil profile (documented up to 170 feet) and gather various salts that are in turn secreted by its foliage. As this salt laden foliage falls from the plant it concentrates around the plant’s base and raises the soil pH to the extent that other plant species are unable to grow. Tamarisk is capable of spreading by root and seed. The presence of tamarisk in our native riparian ecosystems also poses an increased risk of wildfires due to the fact that tamarisk foliage contains volatile oils that can burn easily, even when green. Tamarisk has a very high evapotranspiration rate and consumes large amounts of water daily (30-200 gallons\day).

Much like tamarisk, this perennial shrub\small tree is one of the most widespread and damaging noxious plant species in Huerfano County. Russian olive and tamarisk share many of the same traits such as their ability to form large monocultures that prevent native plant growth, high water consumption and an ability to reproduce by both root and seed. The Huerfano and Cuchara Rivers (along with many tributaries) are heavily infested with both species. Russian olive tends to be the dominate species in the western portions of the county while tamarisk is more dominate in the eastern riparian areas. Russian olive greatly impedes access to water sources due to its dense growth habits and defensive nature. Younger Russian olive stems\limbs bear up to 2” long thorns and mature plants often have a far reaching, over arching canopy that regularly provides over 90% ground enclosure. As both\either species become established along waterways the stream channel becomes greatly constricted. This channel constriction not only eliminates the ability for native cottonwoods and other desirable species to reproduce, but also lowers the carrying capacity of the streambed so that flooding and debris blockage is much more likely.

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