Here’s a look at some of Colorado’s most common noxious yard weeds, and ways to fight back against them.
Myrtle spurge
“This is the poster child for noxious weeds,” says Steven Anthony, Garfield County noxious weed coordinator. With its fleshy green leaves, yellow flowers and low, spreading growth pattern, myrtle spurge is a common ground cover in residential rock gardens and Xeriscapes. Now it’s escaped its backyard bounds, crowding out other native vegetation. Even worse, it has a milky, latex sap that can be poisonous to animals and can cause skin irritation in humans.
You can dig it up, but make sure to pull it out by the roots and wear rubber gloves and eye protection to shield you from the milky sap. Anthony says another nonchemical option is to cover the plants with black plastic and suffocate them. According to the Colorado Department of Agriculture, the most effective chemical control is a 2,4-D herbicide like Weed B Gon or Trimec. Seeds can linger in the soil for eight years, so check the area to make sure no new plants pop up.
Canada thistle and common mallow
These can be hand pulled, but dig deeply to get the taproot, says the Botanic Gardens’ Krishnan. They can also be killed with most herbicides.
Bindweed
With its creeping stems that can wind around any unmovable object, bindweed is one of the most competitive perennial weeds. According to the Larimer County Weed Control District, bindweed has an extensive root system, making it hard to pull out completely. Roots can store two to three years worth of food, and seeds can stay viable in the soil for up to 40 years.
How to get rid of it: The state ag department offers free bindweed mites – microscopic bugs that feed on bindweed leaves and stems, stressing them and eventually killing the plant. Don’t expect instant eradication, though. State Weed Coordinator Kelly Uhing says you’ll see results in a year or two, but Denver Botanic Gardens’ Director of Horticulture Sarada Krishnan says it’s more like four or five years. The mites are shipped on bindweed stems from the ag department’s insectary in Palisade, 866-324-2963 or ag.state.co.us/csd/insectary/index.html.
According to Larimer Weed Control, pumpkin vines are another nonchemical option; they help to reduce bindweed’s competitive tendencies.
Colorado State University’s cooperative extension service recommends applying an herbicide such as Weedone, Turflon or Trimec to bindweed in mid-April through early June, or September to October. If the herbicides are sprayed in the hot summer months when the temperature is over 85 degrees, Uhing says they volatize and travel to other plants.
Downey brome, nutsedge and cheat grass
The trick is to pull, mow or spray these grassy weeds before they go to seed. “It’s called cheat grass because it cheats all the other grasses by seeding early,” Krishnan says. You may already be too late this year, so make plans to zap these weeds next spring, shortly after they appear in your yard.
For more information on noxious weeds, visit the Noxious Weeds of Colorado website,
Beneficial weeds
Weed experts insist there all no beneficial weeds, but Krishnan takes pity on those of us who love our dandelions. Butterflies also love dandelions, she says, and painted lady butterfly caterpillars eat thistles. Monarch butterfly caterpillars are particularly partial to milkweed, she says.
Going organic
Hate herbicides? Some people opt for vinegar as a weed killer, but there’s debate as to how effective it really is. The U.S. Agricultural Research Service found in a 2002 study that not only is vinegar cheap and environmentally safe, but it also kills common weeds.
Scientists hand-sprayed vinegar on Canada thistle, common lamb’s quarters, giant foxtail, velvetleaf and smooth pigweed. They found that 5 percent and 10 percent concentrations killed the weeds during their first two weeks of life. Canada thistle had a 100 percent kill rate at a 5 percent concentration–the amount found in household vinegar.
But don’t overspray, Krishnan says. Too much vinegar can make your soil acidic, which is good for many fruits and vegetables but bad for grass and some other plants.
