TELLURIDE – San Miguel County will begin treating areas of the Valley Floor with herbicide as early as Friday, weather permitting, in an attempt to control the spread of noxious weeds that threaten its native riparian vegetation.
“We want to get out there as soon as possible but need good dry ground and ideal conditions,” said Sheila Grother, San Miguel County Weed Manager.
This is the first time the county has been able to address the spread of invasive plants on the 572-acre parcel because it did not have access to it until Telluride won its lawsuit against the San Miguel Valley Corporation and took ownership of the property in June.
“They’ve got some big issues they’re going to have to address,” Grother said.
Five species of noxious weeds will be targeted: Canada thistle (Cirsium arvense), musk thistle (Carduus nutans), oxeye daisy (Chrysanthemum leucanthemum), scentless chamomile (Matricaria perforata), and yellow toadflax (Linaria vulgaris).
While the state of Colorado has designated none of the five species for mandatory eradication, all are among those for which the state joins with local governments to develop and implement management plans designed to stop the plants’ continued spread.”
Both the Canada thistle and the oxeye daisy have the ability to completely take over the native vegetation.
“Those are a huge danger to the riparian area,” said Grother.
Yellow toadflax is a particularly difficult species to eradicate because, like aspen, it is capable of reproducing both with seeds and by sending off shoots in its root system. The visible part of the plant represents only about 25 percent of its total; the rest is a huge underground root system, according to Grother.
Among the five plants, musk thistle is the only one that could potentially be removed manually with any success, she continued.
“The idea of pulling weeds on the Valley Floor is very appealing, but it’s going to be very, very slow to be effective; and in the meantime these plants are going to spread,” she said.
Noxious weeds represent somewhere between 10 and 15 acres of the total Valley Floor vegetation, according to Grother.
“If left to its own devices for 10 years, I could easily see that being tenfold,” she said.
The county hopes to treat between two to three of the worst weed-infested acres during its three-day spraying campaign. It will use an herbicide containing the active ingredient aminopyralid, which Grother chose because of its comparatively low toxicity and low use rate with not more than seven ounces of the chemical applied for every one acre.
“This is as benign a chemical as I can come up with,” she said. “I think this is the best we can find.”
Aminopyralid is classified under the U.S. Department of Environmental Protection’s Reduced-risk Initiative that expedites the registration of conventional pesticides believed by the EPA to pose less risk to human health and the environment than existing alternatives, according to the agency’s website. They are said to have a low impact on human health, pose lower toxicity for birds, fish and non-target plants, contain a low potential for groundwater contamination, and require that less active ingredients be used than conventional alternatives.
However, this past June controversy arose in the United Kingdom where home gardeners were advised to not eat the vegetables they had grown after their gardens were contaminated with the chemical, according to The Observer.
The deformed and withered vegetables appeared to have come into contact with aminopyralid after gardeners composted or mulched food plants using purchased manure produced by animals fed with treated forage, despite warning labels against the practice.
At press time a notice appeared on the website of Dow AgroSciences, the chemical’s manufacturer, advising that sales and use of the herbicide had been suspended in the U.K. “until assurances can be given that the product and subsequent treated forage and resultant animal wastes will be handled correctly.”
Rather than conducting a wholesale spraying of the selected areas, the application of the herbicide will be targeted and applied via handgun from an all-terrain vehicle or, in areas too delicate for vehicle traffic, from four-gallon backpack sprayers carried by county workers.
“We want people to understand what we’re doing and why; that we’re not just randomly tossing herbicide into the environment,” said Grother.
Should any other noxious weeds be encountered, and Grother believes they may well be, they will also be sprayed.
Not the dandelions, though.
“We’re not dealing with dandelions other than where it’s co-located [with the target species],” Grother said.
“There’s way too much out there to make any effort of control.”