Weber County Yellow Starthistle

Quick and Effective Control of Yellow Starthistle

The Weber County Yellow Starthistle project began in 2019 when yellow starthistle had become problematic throughout Weber county on mountain sides and even within city limits. The Davis and Weber County’s Conservation Districts have excelled at organizing and implementing this project.

Yellow starthistle is a biennial/ winter annual that reproduces through seeds. On average, a plant can produce up to 120 seeds, but in optimal conditions, it can produce up to 100,000 seeds (USDA-NRCS). It can outcompete other beneficial plants and can cause the deadly chewing disease in horses. This is particularly problematic as there is a large infestation of yellow starthistle at the Weber County fairgrounds horse obstacle course.

What we did

For treatments, backpack and aerial sprays have been used with Milestone at 7oz/acre and/or Esplanade at 6 oz/acre, and some biocontrol have been implemented.

For monitoring, we at UDAF, installed sites at the Weber County Fairgrounds and near the Memorial Gardens Cemetery. 

Average % cover

At the Memorial Gardens Cemetery, we installed 6 transects. Three of the lower transects were sprayed in the fall after the initial monitoring. Three of the upper transects were sprayed in the following spring. After the initial treatment, the cover dropped quickly from around 21% cover to 0% cover on the transect. At the Weber County Fairgrounds, the cover was slightly higher initially, and by 2021, the cover dropped to trace amounts (<1% on average). This indicates that the spraying has been very effective for this species. We would recommend continued spot spraying to ensure the species does not rebound.

Overall, this project has done an excellent job at controlling yellow starthistle. However, there are many other noxious weeds of concern occurring on the sites, low native cover, and decreased vegetation cover in general. There are many things that could be impacting the cover of other plants, but if these do not improve, other measures may need to be taken to prevent noxious weeds from returning.

Yellow starthistle infestation

Utah Department of Agriculture and Food

UDAF funds projects on a SIIPA score method

To learn more please visit https://utahweedsupervisors.com

Utah Department of Agriculture

Aaron Eagar

Mapping and reporting

Average % cover

Utah Department of Agriculture and Food