The Larimer County Department of Natural Resources weed workgroup manages invasive plant species on over 30,000 acres in 27 parks and open lands. 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, visitor usability of natural areas and negatively impacts the economy. 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 invasive exotic 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:
Every property presents unique challenges that must be taken into consideration when developing a weed 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.