Drought, development and fires open door to invaders
|Musk thistle blossoms cover the roadside along Florida
Road just east of town on Tuesday. The plant is not native to the area
and as such, has no predators, which allows it to grow and spread unchecked.
Although the most recognizable invader in the county, Rod Cook, La
Plata County weed manager, said there are other noxious weeds that
are far more worrisome for the local region./Photo by Todd Newcomer.
A t first glance, the yellow centered daisy almost passes as a wildflower.
But a deeper look at an area like Needles or Durango Mountain Resort
reveals a vigorous, almost cancerous spread of the plant. In fact, the
attractive oxeye daisy, a noxious weed, exists in abundance throughout
La Plata County.
"To me, that's the trait of an aggressive weed," said Rod Cook, La Plata
County weed manager. "It can grow in a variety of elevations and degrees
of moisture and temperature. I've seen oxeye daisy above treeline near
Molas Pass, growing out of shale in Ridges Basin and growing out of pine
needles in stands of ponderosa pine."
Cook also has bigger concerns than just getting a grip on the spread
of oxeye daisy. A major invasion of weeds of all types has come on the
heels of the last five years of drought in Southwest Colorado. And while
invasive weeds may seem to be spreading unchecked locally, so is local
awareness. Cook and others see a bright future for La Plata County as
it works to stem the spread.
Noxious weeds are plants that are not native to the region and consequently
have no natural predators. They either arrive as seeds riding on clothing,
vehicles, wind or pets or are sold as ornamentals by some nurseries and
garden centers. Once established, they are difficult to eliminate. In
addition to gobbling up thousands of acres, noxious weeds also squeeze
out natives. Of Colorado's 3,000 native plant species, approximately
500 have already been displaced by the spread of weeds. Although this
statistic may seem alarming, Cook said that Colorado is actually in much
better shape than many Western states.
"We're not in the same bad way as a lot of other states," he said. "The
spread of weeds is unbelievably vast up in places like Western Montana
However, things are also particularly difficult for Southwest Colorado
at this point of major housing growth and limited rainfall. The lingering
drought has failed to sustain native species and opened the door for
invaders, according to Cook.
ally in the war against weeds
Tired of digging up musk thistle by the roots?
Help could be on the way from a surprising source.
The recent return of moisture to the region has
also brought the return of the seed head weevil,
an insect that was introduced in the early 1980s
to feed on thistle. It had been presumed that
drought eliminated the bugs, but numerous egg
cases have been observed this season.
Rod Cook, La Plata
County weed manager, said, "It
took 20 years for the number of bugs to grow
to the point where they were effective. Then
in 2002, they crashed. That's why we're now seeing
thistles that are 6 and 7 feet tall all over
The seed head weevil feeds exclusively on the
musk thistle seeds during its larval growth stage
and destroys most of the seed production. The
reappearance of the bugs appears to be a natural
recovery response, but they also need a little
Cook explained that shoveling thistle, disposing
of flower heads or spraying adult thistles will
interrupt the weevils' life cycle and ultimately
lead to more musk thistle. Instead he encouraged
people to leave the adult thistles and weevils
alone during the summer and control the new thistle
rosettes, next year's plant, during September
"The weevils may come back in just a few years
if we have favorable conditions," Cook said.
"The challenge for this office has been educating new land owners and
working to deal with weeds in a drought situation," he said. "A drought
always increases the frequency of weeds. We've been
dealing with this drought since 1998, and we're going
to have to pay for it for a long time."
Cook explained that the drought and earthwork are similarly attractive
for invasive weeds. In both cases, existing life is erased from the land
and traveling or dormant seeds have an easy time getting established.
"There are voids in the vegetation and nature abhors a vacuum," Cook
said. "It's going to fill it with something, and it's not always desirable.
Weeds are just a symptom of something that's happened on the land."
Nicole Smith, program director for the San Juan Mountains Association,
explained that fire is another form of disturbance that is attractive
to weeds. She pointed to sections of public lands burned during the 2002
Missionary Ridge Fire and a section near Lemon Reservoir that burned
at an earlier date.
"You would always hope that with rehabilitation efforts, the natives
would come back," she said. "But with disturbed areas, the weeds have
also come in quickly."
Cook said that the most recognizable weed for residents in La Plata
County is the Musk Thistle. He added that although it seems unpleasant,
it is also relatively easy to eliminate.
"The Musk Thistle is the one that everybody objects to and the one I
get the most calls about," he said. "Then I usually go out for a site
visit and show them some others that are bigger problems."
Citing bigger problems, Cook explained that in western La Plata County,
Russian knapweed, a serious noxious weed that is also poisonous to livestock,
is a growing problem. Leafy Spurge, the most serious weed threat in the
state, is getting a foothold in the southern areas of the county. Oxeye
daisy has spread throughout the northern end of the county. And yellow
toadflax, a snapdragon that was introduced as an ornamental, has spread
vigorously through areas like Wildcat Canyon.
However, people are also beginning to understand the problem and getting
serious about managing weeds throughout the county. Smith noted that
SJMA has been actively working to educate people through weed walks and
"We've been focusing on public education on weeds and trying to create
a general knowledge about them and the impact they can have on public
and private lands," she said.
Smith added that awareness in La Plata County is actually quite strong. "I'm
impressed by how many people are aware of the noxious weed problem," she
said. "And I think awareness is the first step toward dealing with the
Cook agreed that local people are definitely concerned about stemming
the local spread of weeds. "I think we have a high level of interest," he
said. "I get a lot of calls in this office every day, and I do a lot
of site visits."
And while Cook said that eradicating noxious weeds can be difficult,
there are many signs of hope. As an example, he pointed to a local woman
who purchased 40 acres that was infested with leafy spurge, spotted knapweed,
Russian knapweed, yellow toadflax, musk thistle, Canada thistle and a
wide variety of mustards.
"She went after it with a vengeance," he said. "Not long ago, I got
a call from her and she asked me to come out and have a look. She had
virtually cleaned it up by herself over a five-year period."
For more information on weed identification and weed management log