Weed Management in Open Lands Areas
The Larimer County Natural Resources weed workgroup manages invasive plant species on over 26,000 acres in 27 parks and open land properties. Invasive, non-native plants are known as noxious weeds and most are listed under the Colorado Noxious Weed Act. Noxious weeds threaten the ecological integrity and visitor usability of natural areas. Noxious weeds adapt easily to different eco-systems, displace native plant communities and wildlife, and can potentially thrive in Larimer County. Weed specialists take an integrated management approach to contain and control these alien plants. By incorporating various methods of control and suppression, the long term management of invasive plants is more successful and sustainable. Individual integrated weed management plans are devised, implemented, monitored, and then revised for each of the parks and open lands properties:
- Carter Lake
Carter Lake is a reservoir tucked into the foothills to the west of Loveland, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Land Management and the Northern Colorado Water Conservancy District. The vegetation surrounding Carter Lake is managed by Larimer County Department of Natural Resources. The public park surrounding the lake occupies 1,000 acres of Ponderosa Pine woodlands. Noxious weeds of concern in the area include: Canada thistle, common mullein, moth mullein, musk thistle and yellow toadflax.
Herbicide applications targeting the thistle species below the dams have been quite successful in recent years. Monitoring and weed mapping in these areas has revealed a significant decrease in both Canada and musk thistle.
In 2008 yellow toadflax was found below the dam at the bottom of the Eagle Wind Loop campground. This species is targeted for eradication in the years to come. Although the abundance of this plant is somewhat minimal, removing it may prove to be a challenge because of its ability to reproduce rapidly and resist most herbicide.
- Devil's Backbone
The Devil's Backbone Open Space occupies 685 acres to the west of Loveland, CO. The trailhead is the starting point for the Blue Sky trail that proceeds north to Horsetooth Reservoir. The topography varies from gently sloping rangeland to steep cliffs and hogbacks. The native vegetation is mainly grassland and mountain mahogany shrub land. The noxious weeds that are present include: Canada thistle, downy brome, kochia, musk thistle and Russian thistle. Weed management on the Devil's Backbone includes weed whacking the Canada thistle and kochia, and selective herbicide applications.
On the Indian Creek portion of the Devil's Backbone the site appears to have been heavily impacted by domestic livestock grazing prior to the county's acquisition, resulting in a plant community dominated by downy brome and Japanese brome(both plants are also known as 'cheatgrass').
In 2007, Larimer County Department of Natural resources began to restore the native plant community in the Indian Creek valley. Restoration efforts consisted of a variety of management activities designed to suppress and/or control large portions of cheatgrass, and shift plant community dominance to native perennial species.
Management activity began October 2007 with a prescribed burn of 40 acres on the south end of the valley. Vegetation managers wanted to conduct the burn after cheatgrass seed had germinated, which was mid-August in 2007. The standing dead stalks (or thatch) serve as fuel to carry the fire and generate enough heat to kill newly emerged green cheatgrass at ground level. Cheatgrass seed, imbedded in the thatch layer at ground level, typically survives the burn. Perennial grasses survive and cool season species, such as western wheatgrass, are exposed to sunlight and produce new growth.
Subsequent flushes of cheatgrass following a fall burn are expected, and occurred at this site in November 2007. At the first opportunity, Plateau was applied in March 2008 across the burn area for selective control of the cheatgrass' second flush.
In the spring, a 40 acre section of cheat grass further north on Indian Creek was similarly managed. A spring burn can be more effective than in the fall because a subsequent flush of cheatgrass will not occur. However, it is possible to have snow cover present, or previous heavy winter snows can lay down enough moisture to prevent a fire from carrying.
Sheep grazing was then utilized in April of 2008 for cheatgrass suppression on the west side of the service road. Approximately 1000 sheep grazed a five acre area. A second grazing was planned for May, but the presence of bighorn sheep in the vicinity put an end to domestic sheep grazing. It was feared that the domestic sheep could potentially spread lungworm to the bighorns.
- Eagle's Nest
Eagles Nest Open Space occupies 755 acres south of Livermore. The topography varies greatly from rolling grasslands - to foothills - to large hanging cliffs. Riparian habitat is found along the North Fork of the Poudre River running through the middle of the property. Native vegetation includes grasslands, mountain mahogany shrub lands, and ponderosa pine woodlands. Pastures are leased to ranchers for cattle grazing. Noxious weed management has been ongoing and arduous at times since the purchase of the property in 2001. However, significant reduction in invasive plant species has been achieved.
Noxious weeds of concern at Eagles Nest include: Canada thistle, dalmatian toadflax, cheatgrass, leafy spurge, musk thistle and Russian thistle. Leafy spurge is the most difficult to manage. Most effective control requires two separate herbicide applications: first in the spring to inhibit the spread of seed and again in the fall to target the roots during the translocation process. Dalmatian toadflax is managed with herbicide in the fall once new growth is found at the base of the plants. These two perennial weeds are especially challenging because there appears to be only a brief period of time that they are very susceptible to herbicide. The Larimer County weed work group is currently looking into releasing mecinus janthinus, an insect bio-control agent that targets dalmatian toadflax, onto the steep and inaccessible hills at Eagle's Nest to the west of the river.
- Flatiron Reservoir
Flatiron Reservoir is in the foothills, north of Carter Lake and west of Loveland, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Land Management and the Northern Colorado Water Conservancy District. The vegetation around Flatiron Reservoir is managed by Larimer County Department of Natural Resources. The public park surrounding the lake occupies 200 acres of mountain mahogany shrub lands, native plant communities and campgrounds. Noxious weeds of concern in the area include: Canada thistle, common mullein, diffuse knapweed, moth mullein, musk thistle and Russian olive trees.
An application in June with a selective herbicide is used to control the various weeds at Flatiron Reservoir. Musk thistle and common mullein is removed by shovel on rainy and windy days.
- Fossil Creek
Fossil Creek Open Space is located west of I-25 and north of Highway 392. The open land occupies 836.5 acres and has trails that lead to Swede Lake where bird blinds are setup for wildlife viewing. The primary vegetation at Fossil Creek is comprised of cottonwood trees, willows and native grasslands. Noxious weeds of concern at Fossil Creek include: Canada thistle, hoary cress, leafy spurge, musk thistle and Russian knapweed. In 2010 Fossil Creek management will be transferred to the city of Fort Collins.
The Open Space property was under agricultural production prior to acquisition by Larimer County. Much of the property has been restored to native vegetation. The most recent restoration project is on a 60 acre portion on the southwest corner of the property, bounded by Carpenter Street on the south and the Water Treatment Plant to the west. The 60 acre area was formerly smooth brome grass, a non-native species grown for hay production, and undesirable on a site being restored to a native plant community.
The project began with an herbicide application on the smooth brome in June of 2007. In December of 2007 the site was plowed. The plowing served two purposes: to prevent re-growth of smooth brome by disrupting the extensive root system of the perennial grass and to alleviate soil compaction for better root development of the native grasses to be planted.
In June of 2008, sorghum was planted on the 60 acres. The sorghum variety was a sterile hybrid (produced no viable seed) to ensure volunteer sorghum would not be a problem in future years. The sorghum plants die off after a hard frost in the fall, but the stalks provide cover for the grasses to be planted. Sorghum stalks catch blowing snow and prevents topsoil from blowing while grasses are establishing.
A mix of native grass species was planted in December of 2008. The grass seed was drilled between the rows of sorghum stubble, and with adequate spring moisture should emerge in the spring or early summer in 2009.
- Hermit Park
Hermit Park is south east of Estes Park on US highway 36. This park's topography varies between rolling mountains and pristine grass meadows. The vegetation is comprised primarily with ponderosa pine woodlands and native grasses. Hermit's Park was purchased by Larimer County Natural Resources in 2007. This park is new to the county therefore, weed specialists are working diligently to scout the entire area and map key weed infestations. Some of the noxious weeds of concern include: Canada thistle, diffuse knapweed, musk thistle and yellow toadflax.
In early summer 2009 the diffuse knapweed will be targeted for eradication at the main entrance of the park. Selective herbicides will be applied before flowering, and the unaffected plants will then be pulled and bagged. Later herbicide applications will take place to control the thistle and yellow toadflax.
- Horsetooth Mountain Park
Horsetooth Mountain Open Space occupies over 2,700 acres of land to the west of Horsetooth Reservoir. The topography varies greatly from meadows to cliffs, and the vegetation consists of ponderosa pine woodlands, mountain mahogany shrub lands and native grasses. The noxious weeds of concern include: bull thistle, Canada thistle, common mullein, dalmatian toadflax, moth mullein, musk thistle and myrtle spurge.
Myrtle spurge, being an A list species, is targeted for eradication in the park. Currently three small infestations are known to exist. Myrtle spurge can be controlled through hand pulling if enough of the root is ripped out of the ground.
Early in the summer, all invasive thistle species are targeted with a selective herbicide. Late in the fall, dalmatian toadflax is targeted with a selective herbicide.
- Horsetooth Reservoir
Horsetooth Reservoir is tucked in the foothills to the west of Fort Collins, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Land Management and the Northern Colorado Water Conservancy District. The vegetation surrounding Horsetooth Reservoir is managed by Larimer County Department of Natural Resources. The public park surrounding the lake occupies 2,000 acres of Ponderosa Pine woodlands and mountain mahogany shrublands. Noxious weeds of concern include: bull thistle, Canada thistle, common mullein, dalmatian toadflax, houndstongue, leafy spurge, moth mullein, musk thistle poison hemlock, tamarisk/saltcedar and yellow toadflax.
Due to steep terrain and the lack of four-wheel drive access to areas that are heavily infested with Dalmatian toadflax, in 2008 weed specialists from Larimer County and APHIS (animal and plant health inspection services) released the insect bio-control mecinus janthinus; a stem boring weevil. The project is a collaborative research effort to institute the best management practices for the area. It is the hopes of county weed specialist and APHIS that the mecinus janthinus will establish an abundant population and control the Dalmatian toadflax. The release area could then be used as a nurse site where insects would be collected and relocated. At Horsetooth Reservoir there have also been releases of the aphthona insect; a flea beetle, which targets leafy spurge.
Selective herbicides are also utilized throughout the late spring, summer and fall. When the water level recedes in August, the weed work group uses boats to access the Canada thistle and musk thistle that grow below the high water mark. Selective, aquatic labeled herbicides are then used to diminish the seed banks and control the invasive thistles. Aquatically labeled herbicides are scientifically proven to provide the most effective control without damaging water quality or aquatic wildlife at the recommended rates.
- Lion's Park
Lion's Park occupies 20 acres outside of Laporte, CO. This day use area serves as a picnic ground, trail head and wildlife area. The Pleasant Valley Trail follows the Poudre River through the property. This riparian area hosts a variety of vegetation from cottonwood trees and willows to wildflowers and grasses.
The noxious weeds that are present include: Canada thistle, Dalmatian toadflax, field bindweed, and leafy spurge. Weed densities have been significantly reduced, and management efforts consist primarily of monitoring the site and spot-spraying as necessary.
- Pinewood Reservoir
Pinewood Reservoir is north-west of Carter Lake and west of Loveland, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Land Management and the Northern Colorado Water Conservancy District. The vegetation around pinewood Reservoir is managed by Larimer County Department of Natural Resources. The public park surrounding the lake occupies 327 acres of ponderosa pine woodlands, mountain mahogany shrublands and native grasslands. Noxious weeds of concern include: Canada thistle, common mullein, diffuse knapweed, moth mullein and musk thistle. The state of Colorado 'list A' noxious weed myrtle spurge has been found in the subdivision to the north of Pinewood reservoir. If any park visitor sees myrtle spurge along the trails at Pinewood Reservoir, they are encouraged to report it to the Larimer County Weed District Office at (970) 498 5768 or by e-mail at ccisneros@larimer.org.
An application with a selective herbicide in July is used to control the various weeds at Pinewood Reservoir. Musk thistle and common mullein is removed by shovel. The diffuse knapweed is sometimes removed by hand pulling and bagging.
- Pleasant Valley trail
Pleasant Valley Trail is managed by Larimer County from the entrance of Watson Lake to the south end of Lions Park near Laporte, CO. The trail moves through a corridor that could provide habitat for the Prebles Meadow Jumping mouse, a federally listed endangered species. To mitigate for Prebles habitat, Larimer County has partnered up with various other organizations to plant shrubs along the path. To protect these new shrubs, noxious weed management is necessary to limit the plant competition in this area. The noxious weeds of concern include: Canada thistle, common mullein, kochia, leafy spurge, musk thistle and Russian knapweed.
The trail is continuously monitored by vegetation specialists throughout the spring, summer and fall. Herbicide applications are made in the late spring and fall. Some of the invasive annuals and biennials are effectively controlled with shovels and weed whackers.
- Ramsay-Shockey
Ramsey-Shockey Open Space occupies 177 acres of sloped hills with Ponderosa Pine and shrubland plant communities. Ramsey-Shockey hosts a system of trails that interconnect with Pinewood Reservoir. The noxious weeds that are found on the property include: Canada thistle, common mullein, cheatgrass, and musk thistle. The abundance of each species on the property appears to be marginal. Weed management on Ramsey-Shockey includes some digging of musk thistle and common mullein rosettes, mowing of Canada thistle to prevent the spread of seed, and a minimal amounts of herbicide application.
- Red Mountain
Slated to open up to the public in June 2009, Red Mountain Ranch occupies a 14,980 acre area in the Laramie Foothills. The property is part of an effort to preserve the pristine area between Interstate Highway I-25 and US Highway 287 in northern Colorado. Adjacent to the east of Red Mountain Ranch is Soap Stone Natural Area, which is managed by the city of Fort Collins. To the north of Red Mountain Ranch is an area managed by the city of Cheyenne. The landscape at Red Mountain Ranch changes dramatically within its borders. The vegetation includes Ponderosa pine woodlands, native grasslands and mountain mahogany shrublands. The noxious weeds present include: bull thistle, Canada thistle, dalmatian toadflax, cheatgrass, leafy spurge, common burdock, houdstongue, kochia, musk thistle, diffuse knapweed, Russian olive, Russian knapweed, Russian thistle, saltcedar, scotch thistle, and poison hemlock.
At some of the most remote locations on the ranch, researchers from Colorado State University have released 1,800 insect biological control agents, Mecinus janthinus to target dalmatian toadflax. Mecinus janthinus is a stem boring weevil that naturally feeds on dalmatian toadflax. The researchers will monitor the establishment of the insect's populations and their impact upon the target plant.
The leafy spurge that is prevalent in one of the main washes that goes by the trail head is targeted for eradication using a late spring and fall herbicide application. The spring application is intended to keep this weed from going to seed. The fall application targets the plant when it is most susceptible to herbicide. Positive progress managing the leafy spurge has been monitored.
Some Russian olive trees and saltcedars have been removed, those remaining will be eradicated in the next couple years.
- Rimrock
Rimrock Open Space is north of the Devil's Back Bone Open Land. Several trails, including the Blue Sky Trail, converge on Rim Rock and head off to the north, south and east. The property itself is 437 acres of gently sloping rangeland, rocky hogbacks, and steep cliffs. The native vegetation on Rim Rock includes grasslands, mountain mahogany shrublands and skunkbush shrublands. Rim Rock is also home to several threatened plant and animal species. The noxious weeds of concern include: Canada thistle, musk thistle and field bindweed. Weed management on Rim Rock include digging musk thistle rosettes and a minimal amount of herbicide applications.
- Soderberg Homestead
The Soderberg Homestead Open Land occupies 101.5 acres to the west of Inlet Bay at Horsetooth Reservoir. The trail moves north from the trailhead and eventually connects with the Horsetooth Mountain Park trail system. The native vegetation consists of ponderosa pine woodlands, mountain mahogany shrublands and foothill grasslands. The native grasses are host plants for imperiled butterflies in the area. The noxious weeds of concern include: Canada thistle, common mullein, Downy brome, Dalmatian toadflax, myrtle spurge and yellow toadflax. Management consists of hand pulling the myrtle spurge and minimal herbicide applications.
In 2008 the weed work group found small amounts of yellow toadflax and myrtle spurge (list 'A' species) on the Soderberg homestead. These two plants are targeted for eradication in this area. Because of the early detection and rapid response to these two highly invasive species, their further spread is less likely.
Each property presents various challenges that must be taken into consideration when developing a vegetation management plan. For example, in 2008 at Horsetooth Reservoir the steep hills and lack of four wheel drive access made controlling the densely populated Dalmatian toadflax a difficult task. Instead of utilizing herbicides in these areas, weed specialists have had to rely on the release of the insect bio-control Mecinus janthinus, a stem boring weevil, to reduce and suppress the number of Dalmatian toadflax.
Once released onto the target site, these insects are monitored over an extended period of time to assure population establishment and impact upon the targeted weed species. If successful, the weevil will eventually reduce the population of toadflax to an acceptable threshold.
In Larimer County's Parks and Open Lands some of the most troublesome weeds include: Canada thistle, cheatgrass, Dalmatian toadflax, diffuse knapweed, leafy spurge, moth mullein, musk thistle, myrtle spurge, poison hemlock, Russian knapweed, Russian thistle, Russian olive, tamarisk/saltcedar, Scotch thistle, spotted knapweed, and yellow toadflax. These weeds differ in life cycle, habitat, seed production, sheer abundance and the susceptibility to any one given form of control.
Some other invasive plants that the state of Colorado has classified as 'list A' species, which the weed work group is keeping a high level of vigilance for include: Mediterranean sage, orange hawkweed, purple loosestrife and yellow starthistle.
To report the sighting of any 'list A' species or for any question, call the Larimer County Weed District office at (970) 498 5768. Prevention is the greatest tool to protect the natural integrity of the parks and open lands. The cost is less and the benefits far greater if new weed infestations are kept out or controlled early. By understanding what areas are susceptible to weed invasion, how seeds are transported by people/livestock/pets, and how to properly identify weeds, Larimer County citizens and staff can effectively recognize and prevent new weed invaders from appearing on public lands.
Weed seed on dogs and horses may be brought into the parks. Some seeds attach to fur and hair then get carried to new areas. Before and after entering a park do a physical inspection of your animals.
Although the presence of weeds may be inescapable, targeting the highly competitive and abundant invasive plants ensures that native plant and wildlife communities will continue to thrive.
Email • 
RSS • 
Twitter