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.
Remote (satellite photography) Sensing
University of Wyoming graduate student Chloe Mattilio, under the direction of Dr. Tekiela, is 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.
Chloe’s work began with searching out appropriate satellite photography (recent, little or no cloud cover, inclusive of our areas of interest in the Yampa River corridor . . . and reasonably priced!). She then applied a number of sophisticated processes to further refine the pixel resolution of the photography, before processing it into multiple spectral band combinations. These were then further tweaked by applying different contrast, brightness and gamma values—all in an attempt to tease out the subtle spectral differences recorded in each photographic pixel.
The end goal of these processes is to develop an algorithm that can effectively classify each enhanced photographic pixel as to whether it recorded light that was, or was not, reflected from a patch of leafy spurge on the ground. To see a detailed, and more technical, synopsis of her work thus far, click HERE.
Initial results have been very promising, and when Chloe “fact-checked” her preliminary classification results against our ground-based leafy spurge mapping data, she reported an average error of 8.24%. Chloe intends to conduct further ground truthing work during the summer of 2021, with the intention of further refining the classification algorithm. The final step will be to produce a comprehensive map of leafy spurge infestations in the Yampa River Valley.
Invasion Risk Predictive Modelling
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 an important use of management resources to protect the Yampa River corridor, irrigated agricultural lands, and associated uplands.
Starting in 2019, University of Wyoming graduate student Hannah Kuhns, under the direction of Dr. Tekiela, began working on a project to quantify the impacts of sheep grazing, herbicide applications, or a combination of the two on leafy spurge seed production. In 2020 Hannah extended her research to include an examination of the effect of various environmental variables on leafy spurge seed germination rates, as well as the potential for root fragments (such as might be eroded from a river bank during spring floods) to propagate in new downstream environments. Collectively, Hannah's investigations provide new insight into the optimum timing and best management practices for the control of leafy spurge populations in riparian areas.
We are happy to report that Hannah's work is progressing well, and she will be completing her graduate degree this spring. She presented a Zoom seminar on her Master's thesis on April 9, 2021. To view the recording of her very informative presentation (51 minutes) click HERE.