Summit County garlic mustard

Project Summary

The EDRR Weed Control project in Summit County is funded through the Utah Department of Agriculture and Food, Invasive Species Mitigation Fund, and partner matching funds. The project is focused on the Class 1B state noxious weed, garlic mustard (Alliaria petiolate) and the Class 2 state noxious weed, spotted knapweed (Centaurea stoebe (C. maculosa)). In April of 2019, Park City Municipal Corporation, and the Summit County CWMA were awarded $200,000 for the treatment of Garlic mustard and spotted knapweed during the 2019-2020 fiscal year with Park City Municipal Corporation as the fiscal agent.

Along with partner in-house weed control efforts, the project uses four weed management contractors including Providia Management Group (PMG), Ground Solutions, Jesus Reas Landscaping and Ecology Bridge. The main partners include Park City Municipal Corporation, Summit County, Snyderville Basin Special Recreation District, Pinebrook Master HOA, Deer Valley and Vail Resorts. Three priority areas were the focus of work within Summit County: Summit Park and adjacent communities, Snyderville Basin, and Park City.  

Treatment and Data Collection

This is the eighth year of ISM funding to treat garlic mustard, sixth year of contiguous treatment of garlic mustard in both the spring and fall of the same year and first year treating spotted knapweed. It is the third year the project used pretreatment weeding to thin flowering plants for better plant herbicide contact and weeding of remote backcountry locations. The project was given consent by property owners to treat 778 private and public parcels summer and fall of 2019 and 686 spring of 2020. Participation had an 84 percent increase for summer and fall 2019 and 83 percent increase for spring 2020 since 2017. 

This is the second year we partnered with local HOA’s to assist with outreach to their members and obtain access to HOA open space. This allowed for the treatment of 88 populations of garlic mustard on 29 HOA parcels and 50 populations of spotted knapweed on eight parcels during the summer and fall of 2019. During spring of 2020 garlic mustard was controlled on approximately 20 HOA open space parcels and no treatment of spotted knapweed was conducted prior to June 30, 2020. 

During July 1, 2019 through November 2019, approximately 100 acres were weeded with an additional 4000 acres monitored with small patches manually controlled, and 463 acres treated with herbicide and an additional 138 retreated with herbicide. This equates to 14 percent of treatment being hand weeding, two percent being biological control and 84 percent herbicide treatment. Due to multiple germinations of garlic mustard, several sites were treated twice July through November and some three times. Knapweed was generally treated once except a few particularly large populations that were treated twice and one location three times. Spring of 2020 approximately 76 acres of garlic mustard were treated with herbicide and 35 acres hand pulled and 15 acres of spotted knapweed were treated with herbicide and 0.02 acres hand pulled.

Last year was the first year that we required residents to weed flowering garlic mustard before treatment. In previous years it was becoming clear residents were not putting in effort to control their own weeds. The weeding requirement was intended to shift the responsibility from the grant back to the landowner. This requirement increased resident efforts in 2019, however, in 2020, we did not enforce this requirement due to an inability to fairly identify homeowners unable to weed due to COVID 19 impacts. 

Treatment Results

Summit Park is showing reduction in garlic mustard density where consistently treated and the spread to open space has been contained. Of the garlic mustard populations treated in the Summit Park/Timberline and Toll Canyon area, 94% were on private residential property. Spotted knapweed, however, was only present and treated on private residential parcels. Two populations in the Pinebrook HOA showed reduction in number, size and density of patches: while, two other areas showed significant increase. These areas showing an increase in cover experienced fire mitigation activities that likely disturbed soils considerably and slightly increased sunlight. Of the garlic populations treated in Pinebrook, 58% were on private, residential parcels while only 5% of spotted knapweed were on private, residential parcels.

Waterways in Snyderville Basin (i.e. Willow Creek) and Park City (i.e. Poison Creek) are significantly reduced in cover. Areas of Park City along McLeod Creek and the creeks of Thayne’s Canyon had declined boundaries in 2019 but the distribution in 2020 was more similar to historic cover. The largest population of garlic mustard on Deer Valley property was treated with weeding and herbicide in 2019 and cover has been reduced by 95%. The site seems to be following the path of the Masonic Trail population. Neighborhoods that are newer to the program and newly accessed HOA open space had dense populations and tended to have more flowering plants than those treated in the past. The densest population of these new areas is the Crescent Ridge Condo open space which is just down slope from the approximate 30-acre Armstrong population found two years ago. Three transects were surveyed between July 1, 2019 and June 30, 2020. The remaining transects from previous years have all experienced levels of disturbance that would confound results so have been abandoned. Data indicate drastic reduction in garlic mustard at the all locations with the greatest reduction at the Masonic Trail site since first treated in 2018. A minor increase in seedlings was observed spring of 2020 and a single herbicide treatment again left the site with primarily bare ground. The Toll Canyon and 570 Upper Evergreen transects both show signs of native plant establishment, particularly the Toll Canyon site.

Community Weed Pulls

Three community weed pull events and two local community group weed pulls were held Spring of 2020. In previous years, the Summit CWMA held a bounty paying residents per bag of mustard. We brought the program back for the three community weed pulls. By paying $3 a bag, offering native seed and holding an opportunity drawing at each weed pull, we had 68 participants pull 121 bags. Most did not take the per bag payment, preferring native seed, however the kids were driven by the bounty and continued pulling several days after the event and contacted the project manager when they had a pile of bags for pick up.

HOA Outreach Program

Two hundred and forty HOAs in the project area were contacted to assist in the collection of consent to treat on member properties. Eightyfour of these HOAs forwarded on project information and consent collection instructions. Thirty of these HOA’s partnered to treat their open space lands. The Pinebrook Master HOA has become an ongoing partner for the ISM project and is working with Snyderville Basin Special Recreation District to address other noxious weeds and develop a weed program. They have also committed to assist with a weed pull in Pinebrook in 2021. The Summit Park HOA has added noxious weed control requirements and information to their new resident welcome packet and plans to help with a weed pull in Summit Park in 2021. The Summit Park, Pinebrook and Crescent Ridge HOAs have committed to annual garlic mustard pulls events within their communities As many of these HOA open spaces are adjacent to or contain waterways and trails that lead to public open space, treatment of these area is important to reduce reinvasion of public open space.

For more information about this project please contact:

Sara Jo Dickens @ jo@ecologybridge.com