Noxious weeds are notoriously difficult to control and in many cases nearly impossible to eradicate, which is why agencies in La Plata County turn to a powerful tool in their fight against invasive plant species: mapping.

La Plata County’s Weed Management Department and San Juan National Forest rely on mapping to guide their management of noxious weeds, using location and species information to monitor their spread and dictate treatments. It’s especially critical in Southwest Colorado where landscape variability and drought challenge weed managers.

“(Mapping) is really the first step to assess the scope and the type of infestations throughout a greater area. Unless you start doing an inventory, you don’t really know what you have,” said Ben Bain, weed manager for La Plata County.

The county’s Weed Management Department has tracked noxious weeds for more than a decade, first on printed maps before switching to a digital GIS system around 2008 that allows the county to collect data and monitor weeds more actively.

Because of budget constraints and limited staffing, the department had to suspend its noxious weed mapping from 2015 to 2019. But with additional resources, Bain has hired seasonal employees over the last three years and tapped into GIS students at Fort Lewis College who can help survey weed infestations.

With its mapping system, the county can collect data by simply driving along roadsides, relying on digitized terrain for points of reference and Bain’s knowledge of weed species.

“We can identify noxious weeds from the road with really good accuracy,” Bain said. “After a while, you just know what to look for, and then previous years’ data will tell you if there’s a certain type of weed to expect in that general area as well.”

But even with a truck and modern technology, mapping the weeds in La Plata County can be challenging. The Weed Department must cover hundreds of miles of road and thousands of parcels throughout the county’s approximately 1,700 square miles.

San Juan National Forest tracks weeds across about 700,000 acres in its Columbine Ranger District.

“We’ve got a million acres, so it’s hard to map all of that,” said Lindsey Hansen, renewable resources staff officer for San Juan National Forest. “We do really focus on those high impact areas.”

San Juan National Forest’s rangeland program leads the agency’s weed mapping efforts, which typically focus on areas of disturbance like the 416 Fire’s burn area or the land around timber sales where weeds sprout. They also include heavily used trails and campgrounds or other areas where ranchers or recreationists identify problematic weeds.

But while the rangeland program guides the forest’s response to weeds, the Forest Service trains its crews on the ground so they can help in identifying infestations, also partnering with counties and other agencies across its districts to map and treat noxious weeds.

The Colorado Department of Transportation operates its own noxious weed program to tackle infestations along state highways. The transportation agency’s crews identify weed infestations as they patrol highways, serving as critical lookouts because roads are a major source of seed dispersion, Andrew Mangold, special crews foreman for CDOT, said in an email.

The public plays a role, too.

“If people want to come to us with GPS locations of weeds, we take that information and we add it to our map layers,” Hansen said.

In its mapping, the Forest Service records the plant species, the location and any treatment the agency or its partners are doing.

The goal, Bain said, is to have a complete picture of all of the invasive weeds in La Plata County.

The work is critical because of the impacts that noxious weeds have. In La Plata County, poison hemlock and houndstongue can kill grazing animals. Other species can invade grasslands and reduce rangeland.

Russian knapweed produces allelochemicals, which poison other plants, allowing the species to take over entire landscapes and form monocultures in which they are the only plants.

“If these weeds are reducing the biodiversity and natural plants available for wildlife, (they) can have animals migrate to different areas than they used to,” Bain said.

They can even affect recreational access in severe infestations.

Once weeds establish themselves, they can be nearly impossible and costly to remove.

“It’s a financial burden for public land agencies and private landowners,” Bain said.

For agencies and weed managers, mapping is key to battling the many invasive plant species colonizing areas of La Plata County.

“If we’ve got crews out working on trails, but we’ve got a giant weed patch on that trail, they can either treat it or avoid it and not make it worse,” Hansen said. “It’s information gathering and then we can use that information to prioritize where we’re going to do treatments each year.”

In addition to informing treatments, which can consist of chemical, biocontrol (such as insects that harm weeds) or mechanical processes, mapping allows managers to monitor their progress and identify effective solutions, or follow the continued spread of weed populations throughout the county.

Agencies can share their data, helping their partners to improve their plans.

Bain uses the county’s maps to understand the distribution of species, which can be disparate in La Plata County’s variable climates.

“Different weeds have different growth cycles,” he said. “Some plants are more receptive to treatments in the spring versus some that are more in the summer, or even fall. Seeing different patterns in different parts of the counties is really helpful.”

Maps give agencies an advantage over weeds, but they still face an almost insurmountable challenge in La Plata County.

Noxious weeds are better adapted to the harsher climates of the county than many native plant species, and long-term drought has worsened the health of native plants and created patches of bare soil where invasive species can then establish themselves.

“We’ve definitely seen bigger noxious weed issues throughout the years and especially lately because it has been so dry,” Bain said.

Something as simple as shoulder maintenance can disturb soil and reactivate previously dormant seed banks. CDOT crews aim to treat noxious weeds before they produce seeds, but June rains have shortened that time, Mangold said in an email.

Still, CDOT has made progress and drastically reduced weed populations over the last five years, he said.

For La Plata County’s Weed Management Department, weeds are best mapped between mid-June and the end of August when plants are flowering.

But noxious weed mapping is not a panacea.

Preventing the spread of weeds by reducing soil disturbance is the most effective solution, Bain said.

With maps in hand, agencies in La Plata County still face an uphill climb.

“I don’t think we’re going get rid of noxious weeds anytime soon,” Bain said.

ahannon@durangoherald.com