Noxious Weeds Throw a Blanket on Colorado

July 21, 2008

By Beth Partin

When it comes to noxious weeds, Colorado, like many other states, suffers from an embarrassment of riches.

Take myrtle spurge. It seemed perfect for a dryland garden, resembling nothing so much as a yellow-flowered sedum.

But this xeriscape favorite has invaded sunny, dry areas in the foothills, where it carpets slopes and crowds out native vegetation. Despite its good looks, it’s on List A under the Colorado Noxious Weed Act, which means that by law it must be eradicated.

Few homeowners imagine that plants from their yards can wreak ecological and economic havoc. State weed coordinator Kelly Uhing likens purple loose-strife, another once-popular ornamental, to “biological pavement” for its devastating effects on wetlands and ability to outcompete natives.

“We have to protect our wetlands and riparian areas,” she says. “These areas may only make up 3 percent of the state, but over 97 percent of our wildlife depend on them.”

Water, wind, birds, animals, vehicle tires and even our own shoes and socks can carry seeds far from the garden. They take root in disturbed soil and from there infest nearby, once-pristine landscapes.

“Noxious weeds threaten our drinking-water supply, agricultural crops, pasture lands and native habitats,” Uhing says.

According to a Colorado Weed Management Association brochure, “The highly flammable invasive grass cheatgrass has altered the frequency of fire on Western rangelands to the extent that they now take place every three to five years, instead of every 60 years.”

The challenges facing county weed managers are daunting. In Broomfield, one full-time employee and a few seasonal employees are responsible for noxious-weed control on 3,500 acres of open space. A majority of Colorado counties face similar struggles with their weed- management programs.

Broomfield weed coordinator Nathan Kelbe has GPS-mapped most of the infestations and says Canada thistle is his biggest problem.

Broomfield has had good results using imported bugs to reduce thistle stands to the point at which they can be sprayed, and is considering using goats to graze weedy areas.

Kelbe says homeowners can help by talking to neighbors about noxious weeds. Also, go to www.cwma.org for information on noxious weeds in Colorado. The site includes pictures and information on training, events, publications and resources.


Book of weeds

* The Colorado Weed Management Association publishes Noxious Weeds of Colorado (printed book) and Garden Smart Colorado (an e- book). Go to www.cwma.org/weed.htm and click on “Publications” on the left.

* Colorado Department of Agriculture. Go to colorado.gov/ag/csd and click on “Noxious Weed Management Program” on the left.


Colorado’s noxious weeds

Noxious weeds are nonnative plants brought to Colorado that threaten native species. They have no natural controls, such as insects that feed on them, and thus spread quickly. The Colorado Noxious Weed Act categorizes weeds into three lists: List A (eradicate), List B (keep from spreading) and List C (provide additional education, research and biological control resources).


* What: Perennial from Eurasia

* Worst features: poisonous; can project seeds many feet away

* Where it is: xeriscape gardens, foothills, mountains, plains

* Management strategy: List A

* How to get rid of it: Pull it in the spring before it flowers or apply a selective herbicide.


* What: Perennial from Eurasia

* Worst features: overtakes wetlands; can produce 3 million small seeds per plant

* Where it is: gardens, wetlands, along the northern Front Range, with infestations scattered in western Colorado as well

* Management strategy: List A * How to get rid of it: Pull small infestations by hand, getting all the roots; apply herbicides for larger infestations; bag flowers and seeds; and use clean clothing and tools for seed removal.


* What: Biennial. It resembles common mullein but can be distinguished by its pungent smell and scalloped leaves.

* Worst feature: produces 100,000 seeds per plant

* Where it is: rangeland, pasture, roadways in Boulder, Larimer and Garfield counties

* Management strategy: List A

* How to get rid of it: Dig up the rosette or apply herbicides in the spring of its first year; for second-year plants gone to seed, remove entire plant, including at least two-thirds of the root, and dispose of properly.


* What: Perennial from Europe

* Worst feature: extensive root system that stores nutrients

* Where it is: widespread

* Management strategy: List B

* How to get rid of it: Stress the plant to use up its root stores. Plant native species for competition; optimum times for herbicide application are late spring/ early summer and again in the fall. Mow regrowth repeatedly in the summer months.


* What: Tree from Europe

* Worst feature: water guzzler

* Where it is: planted as ornamental in yards, windbreak on farms

* Management strategy: List B

* How to get rid of it: Cut tree down, leaving a small portion of the stump, and treat with recommended herbicide.


* What: Perennial from Europe

* Worst feature: crowds out native plants

* Where it is: foothills, Western Slope

* Management strategy: List B

* How to get rid of it: Pull by hand, making sure to pull entire root system; bag flowers and seed heads.


* What: Perennial from Europe

* Worst features: Has an extensive root system that resists pulling; seeds will sprout for decades.

* Where it is: widespread

* Management strategy: List C

* How to get rid of it: Stress the plant by increasing competition from other plants, spraying or using biological controls (bindweed gall mite can be obtained from the Colorado Department of Agriculture Insectary in Palisade).

Originally published by Beth Partin, Special to the Rocky.


comments powered by Disqus