Walking through dense sections of 3-foot-tall, greenish-yellow noxious weeds along a beautiful stretch of the Yampa River, which otherwise is highlighted by a healthy population of young bald eagles, volunteers tried not to be discouraged.

“We need a million more bugs,” said Ben Beall, Routt County resident and member of the Yampa River Leafy Spurge Project working group.

For the past four years, as well as during a 12-mile educational float trip on Friday, working group members have carefully released approximately 82,000 leafy spurge biocontrol insects. They hope the two types of small flea or stem borer beetles, known respectively in Latin shorthand as Aphthona and Oberea insects, will work to help combat the miles of leafy spurge along the Yampa River from taking over more land in Routt and Moffat counties.

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It is a daunting task.

The invasive weed from Eurasia, first introduced to the northeastern U.S. in the 1820s, is most widespread in Oregon, Idaho, Montana, Wyoming, Colorado, North Dakota, South Dakota, Nebraska, Minnesota and Wisconsin. As of 1979, leafy spurge occupied some 2.5 million acres in North America. By 2005, that grew to an estimated 4.6 million acres in the U.S., according to the U.S. Department of Agriculture.

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The working group is fighting that invasive spread in the Yampa Valley with the support of sponsoring nonprofit Friends of the Yampa, and biologists and staff at organizations such as Dinosaur National Monument. The efforts are hampered by the availability of beetles locally and funding.

But Natural Resource Specialist Emily Spencer, from the National Park Service, told the group stopped along the river banks that her team has applied for $700,000 in grant funding. The funds would be used toward control of invasive leafy spurge and Russian knapweed in the Yampa and Green river basins through the next eight years.

Although the beetles’ only food source is leafy spurge, the insects do not eradicate the weeds. They are just one tool, Beall explained. The hope is that the insects stunt the growth of individual leafy spurge plants over time, producing shorter stems, fewer flowers and a decreased density. Working group members believe the weed invasion would have been much worse by now in the Yampa Valley if not for earlier efforts.

Leafy spurge is persistent, competitive and spreads easily from seeds that float well. The weeds have an extensive root system abundant in the top foot of soil that may grow 15 feet deep. Sheep and goats may eat leafy spurge, but the weeds come back from roots in the soil.

Non weed-free hay may be helping to spread the aggressive weed into additional parts of the Yampa Valley, Beall said.

The educational, scenic float included representatives from U.S. Forest Service, Bureau of Land Management, Routt County commissioners, Friends of the Yampa, land owners and volunteers. Beall said limited releases of the beetles began some 30 years ago by the weed programs in Routt and Moffat counties, and some private landowners.

On the first stop during Friday’s “Show Me” float, the working group planned to release insects in one previously mapped weed patch next to the river between Hayden and Craig. But high spring water flows had washed away that particular patch of leafy spurge. That means those churned up roots washed downstream to infest other sections, Beall said.

Each of the leafy spurge’s flowering shoots produces an average of 140 seeds, and seeds are expelled up to 15 feet when capsules dry. The seeds are viable up to eight years in soil, according to the Colorado State University Extension service. Water, birds, animals and people aid seed dispersal, and waterways are good vectors for new infestations.

At various stops along the river, volunteers swung canvas nets across the tops of the dense leafy spurge to check for the presence of existing biocontrol insects that may have migrated from previous releases. Then working group members collected scientific data in plots before releasing new insects. On Friday, the working group released some 4,000 Aphthona and 200 Oberea insects donated by the Colorado Department of Agriculture.

In the past, volunteers traveled to the leafy spurge beetle nursery on the state land board property at the former Lowry Air Force Base to collect and meticulously separate the insects by hand, and then by breath using aspirators. In the future, volunteers are needed to drive to bug nurseries in Idaho to collect the beetles in abundance, working group volunteer Peter Williams said. The beetles survive for about three days after collection.

In 2022, the working group released some 30,700 leafy spurge beetles. About half of those insects were collected by volunteers, and other were purchased from suppliers in Montana and from the Palisade Insectary run by the Colorado Department of Agriculture.

Beetles also were released last year for biocontrol efforts on BLM property in Tepee Draw in Moffat County, at Yampa River State Wildlife Area, near Maybell and near Loudy Simpson Park south of Craig.

Leafy spurge is poisonous to some animals such as cows and horses, and can cause blisters on humans from the weed’s white milky latex. Infestations impact agriculture, recreation and the economy. The Yampa River Leafy Spurge Project hopes to release up to 100,000 insects annually to boost the population to a self-sustaining level.

Extensive information is available at website YampaRiverLeafySpurgeProject.com.