The Yampa River and its associated agricultural water delivery systems are spreading leafy spurge seeds downstream from large areas of infestation that have occupied floodplain areas between Hayden and Craig for several decades. The presence of leafy spurge in these difficult-to-treat riparian environments presents an especially difficult challenge to land managers.


The YRLSP seeks to address this problem through scientific research complementing local knowledge, aimed at the development of effective and sustainable leafy spurge management practices. To this end, the YRLSP has developed a relationship with Dr. Dan Tekiela, invasive weed scientist with the Department of Plant Science at the University of Wyoming, who has recruited two graduate students to work on leafy spurge research projects in the Yampa River Basin. YRLSP volunteers are also engaged in leafy spurge mapping and biological control monitoring activities.


Leafy Spurge Mapping

Field Maps

In 2019, YRLSP began a two-year project for mapping leafy spurge infestations along the Yampa River. Principle mappers Ben Beall and Peter Williams, aided by a group of dedicated volunteers, mapped 60 miles of the river in mid-July. The Yampa has now been mapped from the upper reaches of the infestation near Hayden, all the way downstream past Craig and through the Little Yampa Canyon. Plans for 2020 include additional mapping from the mouth of the Little Yampa Canyon downstream to the east boundary of Dinosaur National Monument.


Our thanks to the many landowners along the river who graciously allowed us access to their properties for the mapping project. Field maps of the 2019 data have been prepared and are now posted to the YRLSP Maps pages.

Mapping leafy spurge in the Little Yampa Canyon

Remote-Sensing Maps

University of Wyoming graduate student Chloe Mattilio, under the direction of Dr. Tekiela, is also developing remote-sensing mapping technology for detecting leafy spurge infestations across the entire Yampa River Basin, using high spatial resolution, multispectral satellite imagery. Chloe's development of the remote-sensing application includes correlation with the field mapping data being collected by YRLSP.

Predictive Modeling Maps

The leafy spurge invasion in the Yampa River Basin is still in progress—what we see today does not define the potential extent of future infestations. Under the direction of Dr. Tekiela, Chloe Mattilio is also working on an invasion risk predictive model for the basin that will aid leafy spurge control efforts now and into the future.

A primary resource is the extensive spatial dataset that has been developed in nearby Fremont County, Wyoming. Locations of leafy spurge populations have been recorded by Fremont County Weed & Pest for years, resulting in a robust dataset cataloging over 14,000 individual populations. By correlating environmental data for the Fremont County and Yampa River study area infestations (including soil type, texture, and pH; annual and monthly mean climate temperature and precipitation; location slope, elevation, and aspect; as well as infestation proximity to roads and developed areas), Chloe will build a predictive model that can be applied to the Yampa River Basin to identify and map locations where new leafy spurge infestations are more likely to occur in the future.


Integrated Pest Management

Leafy spurge is an extremely difficult species to effectively manage and many standard herbicide management options produce less than satisfactory results. In riparian areas, the problem is more complicated because several of the herbicides used to control leafy spurge in upland areas are not labelled for use near water. Because eradication is nearly impossible for well-established invasions, reducing seed production and the resulting spread of seed to new areas is the most responsible use of management resources to protect the Yampa River corridor, irrigated agricultural lands, and associated uplands.


In 2019, University of Wyoming graduate student Hannah Kuhns, under the direction of Dr. Tekiela, began work on a project to quantify the current seed load produced by leafy spurge populations on the Yampa River, as well as establish best management practices for reducing cover and seed production of leafy spurge in diverse riparian systems. Currently, Hannah’s research is focusing on grazing by sheep, the use of a variety of herbicide applications safe to the water line, and combinations of both grazing and herbicide applications in the same growing season.

Sheep can be an important part of Integrated Pest Management


Biological Control Monitoring

Although conventional herbicide treatment of upland leafy spurge infestations has been the norm in the Yampa River Basin, the use of biological control agents also dates back to at least 1989. Unfortunately, in the early years recordkeeping was sometimes incomplete, and virtually no follow-up monitoring was conducted. In the absence of such data, the relative success or failure of these “legacy” releases was never substantiated.

Leafy spurge biological control involves the introduction of one or more different insect species that have co-evolved with leafy spurge in its original old-world habitats. The most commonly released biocontrol agents in the Yampa River Basin have been flea beetles in the genus Aphthona, as well as a stem-boring beetle from the genus Oberea. Recent investigations have also revealed the presence of another introduced species for which no record of local release has been found, the leafy spurge hawk moth (Hyles euphorbiae). More information on leafy spurge biological control can be found on the YRLSP Resources page.

Leafy spurge biocontrol agents photographed locally in 2019

Left top and bottom: Leafy Spurge Flea Beetles (black and brown)

Right top: Leafy Spurge Hawk Moth Caterpillar

Right bottom: Leafy Spurge Stem Borer Beetle

The YRLSP’s efforts towards establishing a leafy spurge biocontrol monitoring program began in 2018, with the research and compilation of all available records for legacy leafy spurge biocontrol releases in Moffat and Routt counties. The location and year of release for over 40 sites were identified (see the YRLSP Maps pages.) For most of these release sites we also have additional information regarding the type and quantity of biocontrol insects that were released.


Beginning in the summer of 2019, volunteer Tamara Naumann, with help from individuals associated with the local Colorado Master Gardner program, and local, county, state and federal land agencies, began revisiting these legacy biocontrol release sites. Using a sweep-net protocol, the current presence or absence of biocontrol insects at each legacy site was established, and the current condition of the leafy spurge infestation was assessed. Other habitat variables (e.g., geomorphic location, aspect, soil type and dominant vegetation) were also inventoried. After these inventories are completed in 2020, each site will be evaluated for its appropriateness for continued biological control monitoring in the future.

Preliminary results from the 2019 monitoring suggest that past releases of biological control species in the Yampa Basin have been more persistent than was conventionally thought. At least one biocontrol species was found at virtually every visited legacy release site where leafy spurge was still present. Both Aphthona and Oberea were also observed in additional locations miles from any known release site (see the YRLSP Maps pages for these results).

Sweeping for leafy spurge biocontrol insects

Monitoring data will also contribute to a better understanding of the resiliency of the various biological control species in association with differing environmental conditions. This information will be invaluable for establishing enhanced biocontrol populations through additional releases in the future. Ultimately, YRLSP hopes to establish a number of viable nursery sites for local-sourced beetle releases.

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