The Summit County Sage-grouse project has the overall goal of improving habitat for sage-grouse and is funded by the Forest Service. One of the ways this project is improving habitat is by controlling noxious weeds in the Sagegrouse Management Area. The Summit County Weed Department has been working closely with both the Forest Service and private land owners to control noxious weeds, and they asked the Utah Department of Agriculture and Food, to assist in monitoring the changes in the noxious weeds at three sites.
This project area is located in Summit County and is very large, encompassing about 305,193 acres (Fig. 1). UDAF monitored a much smaller portion of that by installing three 100 ft. transects. The transects were located on two different private properties, east of Coalville and off Chalk Creek Road (Fig. 1). Both properties utilize the land for grazing and provide great habitat for wildlife
The main noxious weeds found on site are thistles, primarily musk thistle (Carduus nutans) but also Canada thistle (Cirsium arvense) and Scotch cottonthistle (Onopordum acanthium). In 2020, UDAF also discovered trace amounts of houndstongue (Cynoglossum officinale).
Musk and Scotch thistles are biennials that spread with easily dispersed seeds.1,2 These thistles are incredibly difficult to eradicate because the seeds can remain viable for long periods of time. Musk can last up to 15 years in the soil.3,4 Scotch thistle seeds can last up to 39 years.2 They can grow in thick stands that outcompete other more desirable plants.4 In fact, research has found these species have allelopathic qualities.2,5 Also, the spines on the plant inhibit grazing, human recreation, and likely movement of wildlife
Unlike musk and Scotch thistle, Canada thistle is a perennial plant that spreads quickly through both seeds and rhizomes (creeping roots).7,8 As a result, it is very difficult to control.9 Canada thistle outcompetes other desirable plants and will form monocultures.7
Houndstongue was first detected in the 2020 monitoring session on transect 1 and near transect 3. It is not a big problem yet, but it could be if not kept in check. It is a biennial, and it spreads through seeds with barbs that make the seed very sticky.10 As a result, these seeds can be transported long distances, reduce wool quality, and can cause skin and eye irritation in animals.10 Additionally, houndstongue is toxic to horses and cattle and can even result in death.10
Because of the negative impacts of these noxious weeds, controlling them is high priority for not only private land owners, the county, and the state, but also for preserving sage-grouse habitat. The Western Association of Fish and Wildlife Agencies listed Canada thistle as #10 for relative invasiveness in sage-grouse habitats, Scotch thistle as # 17, and musk thistle as # 19.11 Therefore, this project is a great example of multiagency cooperation to meet multiple goals. Annual grasses are another big concern for sage-grouse habitat including cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae).11
This project began both herbicide treatment and monitoring in 2018. Grazing has continued throughout the timeline of the project. For thistles and houndstongue, research has recommended spraying rosettes early in the growing season or in late fall when the plants are actively growing.2,8,10,12 Research has also found that mixing grazing with spraying is one of the most effective ways to quickly control musk thistle.12 The herbicide and time of spraying for this project are on target and recommended by research for all noxious weed species found on the properties (Table 1).2,8,10,12
For monitoring timing, UDAF monitors over a 5 year time frame, but takes a break in year 4. This report is occurring after the third year of monitoring. UDAF monitored in early June for the past 3 years and were able to take pretreatment measurements in 2018.
UDAF personnel went out to the sites to measure changes over time as treatment occurred. To do this, they recorded several observations and took measurements along transects. We used SamplePoint to analyze the photos, and we used excel to calculate the means and confidence intervals to determine changes over time.
After the first year of treatment, the percent cover of musk thistle dropped to less than 2% on all transects. Musk thistle is a biennial with long lived seed source and allelopathic chemicals that suppress the growth of other plants.4,12,13 Therefore, for the first 2-3 years, it is very important to treat all rosettes, even if the cover and density is small. Transect 1 was not treated in year 2. Although, at that time, it only had a 0.3% cover of musk thistle with a small number of plants (1 per m2), the untreated plants expanded to a cover of 33% of the ground by 2020 (Fig. 2 and 3). We would recommend aggressively treating here for at least 2 more years consecutively. Transect 2 also had about 3 plants/m2 in 2019, but after treatment, the percent cover dropped from 1.3% in 2019 to 0.4% in 2020 with no plants found rooted in the transect itself (Fig. 2 and 3). Because there were still trace amounts of musk thistle near transect 2, we would recommend at least 1 more year of spot treating here. Transect 3 had the smallest coverage of musk thistle to begin with, and the plant has not been detected at the site after the first round of treatment. On average, the cover of musk thistle had decreased from 29% to 11%, which is great progress.
By spraying in early summer and using appropriate herbicides, this project has decreased the noxious weed plant cover by 60% while increasing the cover of other plants 16%. The goal of this project was <10% cover of musk thistle and <2% of Canada thistle. They successfully reached their goal for Canada thistle. For musk thistle, the goal would have easily been met if treatments had gone as planned, and if treatments resume, they should easily met their goal by year 5 of monitoring. The increase of non-noxious plants and biodiversity is impressive, and if the sites continue on this trajectory, no other additional restoration activities should be needed (i.e. seeding). We recommend herbicide treatment at transect 1 should begin again with 2 years of consistent sprays. We recommend considering spot spraying transects 2 and 3 at least 1 more time to be sure all thistles and any other encroaching weeds are eradicated. We also recommend checking the sites in the future to ensure noxious weeds are not rebounding, that beneficial plants are increasing, and that erosion is not becoming a problem.
This project report is an excerpt of a complete report prepared by Brittany Duncan, monitoring specialist for the Utah Department of Agriculture and Food. You can download the full report below.
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