Noxious Weeds

Upsetting the Balance: Invasive Weeds in the Estes Valley

Our native grasses and wildflowers evolved over millions of years to fill unique ecological niches. What we know as weeds today (non-native, ecologically damaging plants) did not exist in the Estes Valley prior to human settlement.

Escaping their natural enemies, some non-native plants become invasive, reducing the diversity and quantity of native plants. Weeds rapidly invade areas where the native ground cover is disturbed. This is especially true around any new construction sites in the Estes Valley.

 Why should I be concerned?

• Weeds are a growing problem in the Estes Valley and inside the National Park, seriously detracting from our enjoyment of the natural environment.

• Weed control increases the cost of maintaining both public and private open space.

• Weeds take over important habitat areas for wildlife, displacing native shelter and forage for wildlife while reducing the diversity and quantity of native plants.

• Weeds reduce land values, causing damaging economic impacts in the local neighborhood.

• If left uncontrolled, weeds can dramatically change a visual landscape by completely dominating an area that once held a mix of native species.

• Some weeds thrive because they are poisonous to wildlife. One weed found in the park area, common burdock, has even been documented to fatally trap hummingbirds with its sticky sap.

 The containment of established weeds is very difficult:

• The invasive leafy spurge seed pods build up pressure and explode, shooting seeds 15 feet away.

• Small rodents and birds eat knapweed and Canada thistle seeds, helping to disperse them away from the parent plant.

• Thistles and many other weeds are spread widely by the winds.

• The invasive dyers woad and hoary cress seeds float on water.

• Houndstongue and burdock seeds hitchhike on animal fur (and on human clothing).

In short, there is a pervasive and persistent supply of weed seeds in the Estes Valley just waiting for an opportunity to take root in freshly disturbed ground.

Controlling weeds poses a special dilemma because, once a weed infestation is identified, it is often already so large that containment is labor intensive and expensive. Manually pulling weeds or using machines to dig them up is effective with smaller infestations if done carefully to avoid spreading seeds. Herbicides can be effective in controlling weeds and stopping their spread, especially when infestations are detected early. Effective control generally requires an integrated approach, using a combination of these methods.

Prevention:

Preventing the invasion of weeds is a responsibility shared by all the residents of the Estes Valley , especially those involved in home construction projects. The saying "An ounce of prevention is worth a pound of cure" certainly holds true here.

Prevention requires minimizing soil disturbance resulting from construction activities. Careless site construction activities needlessly damage and destroy native ground cover, creating opportunities for the invasion of weeds. Careful site planning and construction oversight is needed to protect valuable native grasses and wildflowers. This native vegetative cover that is naturally resistant to the invasion of weeds is difficult and expensive to replace. It takes a minimum of three growing seasons to replace native cover.

Once the native ground cover has been disturbed, weeds will immediately invade, “out-competing” the native plants and wildflowers unless preventive measures are taken. Disturbed ground must be reseeded and re-vegetated with native grasses as soon as the construction activity is completed. Usually this requires drilling the desired seed mix into the disturbed soil and hydro-mulching on top to hold the seed bed. The mulch also holds in natural moisture and gives the desired grasses a chance to become established by reducing soil contact with wind borne weed seeds. In some cases slope stabilization with erosion control matting is needed hold the seed and soil in place long enough to establish a new vegetative cover. The semi-arid environment of the Estes Valley presents another obstacle to successful re-vegetation of disturbed sites. Re-seeding measures will be most successful in the spring and early summer when natural soil moisture is most abundant. Seeding during the summer months requires regular hand-watering to ensure substantial germination and rooting.

Early Detection:
It is important to recognize invasive plants before they become established. In order to do this, it is important to be able to identify invasive plants in the seedling or immature stage in addition to the flowering or mature stage. Once a plant has set seed or become established, the amount of effort to manage the plant increases. Known infestations must be contained and prevented from spreading.

Timely Management:
When developing a weed management plan, emphasis must be placed on timely action. Rapid response to an invasive plant problem reduces the amount of time and energy required to keep populations in check. Management options will vary with each weed species. For example, annual and biennial weeds can sometimes be managed with timely cultivation (i.e., before seed set). Herbicides registered for invasive plants have also proven effective in certain situations.

Site Rehabilitation:
Site rehabilitation generally means helping desirable plants to become more competitive after an initial management effort has been implemented to reduce or eliminate an invasive plant. Initial efforts to manage invasive plants prior to rehabilitation efforts may include the use of cultivation, herbicides, and/or biological techniques (check with the Department of Agriculture before using biological-control techniques). If nothing is done to rehabilitate or enhance the infested site once invasive weeds are removed, another undesirable species can take the place of the weed that was removed. Site rehabilitation usually involves reseeding an area, or it may simply involve enhancing the competitive ability of the desirable plants that are still viable on the site. An important part of rehabilitation involves considering the inherent production potential of the site itself (soils, precipitation levels, and topography, etc.).

Links:
Larimer County Weed Control District
Colorado Weed Management Association
Preferred Planting List for the Estes Valley

Questions?  Contact us.