Summit CWMA Garlic Mustard Trials

Summit County 2020-2021

Summary

During 2020 and 2021, the Summit CWMA conducted trial seeding plots in areas where garlic mustard had been successfully treated. The goal was to determine the long-term effects of garlic mustard on soils and native plant germination in forests and forest/sagebrush habitat. Furthermore, researchers wanted to know which seed mixes and soil treatments would result in resistant plant communities in areas of treatment.

Garlic Mustard

Garlic mustard is an aggressive invader that can displace natives, is allelopathic and suppresses the soil fungal community that forest species rely on for resistance to stressors like drought and beetle kill. Forests that have been heavily invaded by garlic mustard are at greater risk of tree mortality which increases fire risk and watershed health concerns. The CWMA has treating garlic mustard in Summit, Salt Lake, and Wasatch Counties as part of the Summit CWMA ISM Garlic Mustard Control Program since 2014. Because garlic mustard impacts wildlife habitat, specifically the Greater Sagegrouse, the work was partially funded with a grant for Sagegrouse habitat improvement from the USDA Forest Service/Utah Weed Supervisors’ Association.

Project Methods

To begin to understand the limitations for revegetation in shaded forest and shrubland areas impacted by garlic mustard, the Summit CWMA established seeding trial test plots in three locations in the Park City and Snyderville Basin areas of Summit County, UT. By testing three native grass seed mixes with soil amendments, researchers wanted to identify a method and species mix for establishing native plant cover and increasing resistance to reinvasion and expansion of garlic mustard.

Findings

As of 2022, researchers had found that seeding with native grasses provides increased native grass establishment following significant reduction of garlic mustard in forests. All seed mixes show high rates of native grass establishment.SummitThe mix of grass species used is important, however whether this difference in success between seed mixes is the result of the full species mix, a smaller subset, or single species is unclear. Blue wildrye is the only species that has produced flowers in these first years. The CWMA will continue to monitor these plots in hope of identifying any additional species that are establishing. One of the clearest results in regards to seeding is that fall application is more effective for all three habitat types and especially for drier sites. Further trials with individual grass species would help to determine which species are driving the responses we have observed.

In addition to seeding, incorporation of soil amendments appears to increase seedling establishment and survival, particularly in maple/oak woodlands and conifer dominated forests. Results from the newly established plots will be helpful in determining if the benefits we have observed using compost and biochar are a result of adding these soil amendments or if seeding alone will result in similar grass establishment. Read the most recent report here.