Non-native and Unchallenged

What distinguishes noxious weeds from other plants is that they are not native to the United States, and they grow unchecked by natural predators and enemies such as insects or diseases. In their native environment, these forces prevent the plant from becoming a problem.

How Noxious Weeds Spread

Noxious weeds become established in soils disturbed by a variety of activities such as construction, motorized vehicles, road maintenance, recreation, improper livestock grazing, and natural disturbances such as fire. Noxious weed seeds are transported to new sites in numerous ways such as wind, water, tires, people, as well as wild and domestic animals.

Environmental Impacts from Noxious Weeds

Biodiversity and ecosystem stability are threatened by noxious weeds. A common characteristic of all noxious weeds is their aggressive, competitive behavior. Typically, they steal precious moisture, nutrients, and sunlight from the surrounding plants. Noxious weeds also alter soil properties, the composition of plant communities, and change the structure of animal communities. Native animals are unable to adapt to using the noxious weeds for food, shelter, or nesting.

Noxious weeds are expanding exponentially in the inter-mountain West. (Courtesy Bureau of Land Management)

Of the 3,000 native species of plants in Colorado, 500 or 17% have already been displaced by noxious weeds.

Carpe weedum: Seize the weeds!

(Weed ‘em and reap; leave ‘em and weep.)

By Irene Shonle, Colorado State University Extension

The success of controlling weeds depends on three things – knowing your weeds, knowing which control method to use, and being persistent. In this article, you’ll find the basic information on different methods of control, and how it can be applied to weeds with different life cycles. Have patience – it can take up to ten years to fully control weeds. This is because it can take that long to deplete the seed bank (seeds that are waiting in the soil) – although most of the seeds will be gone in a few years. Also, reseed with a desirable species to prevent new weed seeds from coming into the bare spot.

Methods of control: The method you choose will depend on the biology of the weed (see more on that below).

Cultural control: Changing conditions to make weed invasion less likely

• Increasing turf or landscape density
• Reducing or increasing water
• Increasing or reducing fertilizer
• Decreasing compaction
• Decreasing or increasing sunlight

Pros: This is the best long-term control: you are increasing the conditions for the plants you want to grow at the same time that you are decreasing the conditions for weeds

Cons: Possibly more expensive and time-consuming; control may not be as fast

Mechanical control: Hand-pulling, cutting, mowing (weed whacker), or smothering weeds (landscape fabric, thick mulch)

Pros: Can be quick, inexpensive; environmentally friendly

Cons: Can be slow and expensive; may not be effective (could even be detrimental at wrong time), landscape fabric can be temporary and hard to remove, mulches and fabrics unfeasible for large infestations.

Biological controls: The use of carefully screened insects to attack portions of the weed (i.e., stems, seeds, flowers, etc.)

Pros: Can be an inexpensive, long-term control solution. Fairly environmentally friendly. Little labor involved.

Cons: Not always effective; requires a large population of weeds to maintain insect populations (won’t work in backyards); does not eradicate weeds; insects can sometimes attack non-target plants.

Herbicide control: The use of carefully screened chemicals to disrupt key processes in plants leading to plant death.

Pros: Effective, cost-effective, quick control

Cons: Can be environmentally problematic, must be used properly to be effective (timing, type, application rate, applicator safety), herbicide resistance can develop, can kill non-target plants, may be difficult to find, or require special licensing.

Weed Biology of Gold Hill’s noxious weeds:

Annuals (Cheatgrass, Scentless chamomile, Redstem filaree)

• The seed germinates in the spring (or fall for winter annual), plant develops and produces seed during the summer (or spring for winter annual), dies with killing frost in the fall (or heat of summer for winter annual).
• Key to control is to prevent seed production and to remain persistent until the seed bank has been depleted. Mechanical and cultural controls often adequate for control. Large areas may need to be treated with herbicides.

Biennials (Musk thistle, Common mullein, Dame’s rocket)

• Requires two seasons to complete growth cycle.
• Seeds germinate in spring; the following season, the plant flowers and matures seeds in summer and fall before dying.
• Key to control is preventing seed production, and depleting the seed bank. These plants are easiest to dig in the rosette or early bolting stage. Mechanical and cultural controls often adequate for control. Large areas may need to be treated with herbicides.

Simple Perennials (Spotted Knapweed, Bouncingbet, Common tansy, Sulfur cinquefoil)

• Possess a root crown that produces new shoots every year. Depend upon seed production to spread; plant will come back every year.
• Key to control: Prevent seed production, kill parent plant, deplete seed bank. Mechanical and cultural controls sometimes adequate for control, but biological or chemical controls may be necessary. Large areas may need to be treated with herbicides.

Creeping Perennials (Canada thistle, Yellow and Dalmatian toadflax, Oxeye daisy, Leafy spurge, Field bindweed)

• Propagate by seed, creeping aboveground stems (stolons) and/or creeping underground parts (rhizomes).
• Key to control: These are the hardest weeds to control. They often have very deep root systems, and pulling can sometimes release adventitious shoots (especially if the plant is well established). Prevent from going to seed, kill parent plant. This often will take several years to fully kill off the parent plant. Often, herbicides will need to be used in conjunction with other methods.

By Susan Fernalld

This year the invasive weeds are surging, using this year’s late moisture to colonize land where native vegetation is thin. Bare soil requires attention to prevent erosion and the rapid in-filling of weeds. The best defense against weeds of all kinds is land that is covered with healthy vegetation.

Here in the mountains where we are all on wells, any large-scale seeding, even using seeds of native plants that grow in our arid environment, is a slow process with only precipitation to get seedlings going. For several years, weeds will predominate especially in dry years, but over years the natives will become established.

Claire DeLeo, Plant Ecologist with Boulder County Parks and Open Space, provided us with a list of native grass species that are appropriate for the Gold Hill area. She first recommends Slender wheatgrass, a tall growing grass, knee height or taller, readily available from any major seed company. It comes in several varieties, and the seed companies can assist you in which variety is best for your area. It is a cool season grass, best sown in the mountains in the spring, providing cover quickly and competition for weeds.

DeLeo’s list includes other good choices for native grasses for Gold Hill: Blue grama, Nodding Brome, Fringed brome, Canada Wildrye, Rocky Mt. fescue, Junegrass, and Western wheatgrass. For those who wish to seed only short grasses for the wildfire defensible space around their homes, their choices in the list are Blue grama, Rocky Mountain fescue, and Junegrass. The seed companies may alternatively suggest Sheep fescue, which looks like Rocky Mt. fescue but is from Europe.

You might want to question the seed companies about where they collect their seed, because seed collected from the plains of Colorado might not survive as well as seed collected from higher elevations. Western Native Seed Company is known to collect from higher elevations. To see CSU Cooperative Extension’s lists of Colorado seed company sources of (not necessarily native) grass seed, click here.

Will you need to amend your soil and fertilize before seeding? Not necessarily if you are seeding with native grass seed, but yes if you are seeding non-native seed, and yes if you are seeding anything after a construction project. In the latter two cases, it would be good to get a soil test and then, if recommended, amend the soil with organic matter such as compost.

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Susan Basabe, Boulder County Planning and Zoning inspector for unincorporated Boulder County and Boulder County Parks and Open Space: 303 441-3930, sbasabe@co.boulder.co.us)

Colorado Department of Agriculture’s Biological Pest Control Section (Insectary):
Toll free 1 866 324-2963 (to order free species-specific insect predators for various noxious weeds)

Colorado’s noxious weed lists A, B and C: http://www.colorado.gov/cs/Satellite/Agriculture-Main/CDAG/1174084048733?rendermode=preview

Boulder County Noxious Weed list: http://www.bouldercounty.org/openspace/resources/weeds/noxiousweeds.pdf

National Pesticide Information Center at Oregon State University:
1-800-858-7378 (NPIC, located at Oregon State University, is not affiliated with the pesticide industry. Its purpose is to give research-based information to the public. The phone is answered by a human being ready for all your herbicide questions.)

Native seed sources:
http://csuturf.colostate.edu/Pages/COseedcompanies.htm.

Your Gold Hill Town Meeting weed committee:

Susan Fernalld 303 447-0634 and sfernalld@msn.com
Paul Roberts 720 565-9062 and juniper50@msn.com