UCCE Master Gardeners of El Dorado County
University of California
UCCE Master Gardeners of El Dorado County

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weed_YellowStarthistle_ C032-07
Don't Wish Upon This Star!
Controlling Yellow Starthistle
By Ada Brehmer and Laurel Rady
UCCE Master Gardeners of El Dorado County

Yellow Starthistle (YST) is one of the most feared and invasive weeds in El Dorado County. It can start germinating with the first fall rains and continue through spring. Spreading quickly through fields and lawns, this weed depletes the limited water in our soil, competes with native plants that support wildlife, and is poisonous to horses. Eradicating YST is an urgent priority in preventing further damage to our environment.

YST reproduces entirely by seed. The seeds drop near the parent plant and can survive in the soil for three years or more. YST matures during the summer months, and plants range from four inches to five feet in height. Leaves are gray-green to blue-green, with stems that are sharp and spiny, yellow thistle-like flowers, and a deep taproot. Removing the taproot is not necessary. However, if YST is allowed to drop its seeds, the infestation continues.

Hand pulling YST before it sets flowers and seeds is one of the most effective ways to control this invasive plant. This can be done any time after germination, but it is easier to wait until late spring when the plants have started to form a stem and the ground is still moist. Once it has been pulled, YST is not able to resprout, so severing the stem from the root is sufficient. Start at the outward edge of an affected area and work inward, to avoid the additional spread of seeds. Bag and tie all plant material and clean your tools and clothing afterwards. Regularly monitor and remove all new weed growth.

If YST has spread over a large area, hand pulling may not be possible and control will probably require a variety of methods. Mowing is most effective on tall, mature plants, when the soil is dry and rain/irrigation will not occur in the following week. Grazing by sheep or cattle should be done before YST’s spines form; goats can effectively graze at any time. Horses should never be allowed near YST.

Replanting the area with a more desirable, fast-growing plant is a good idea, depending on your site’s characteristics and intended future use. For obvious reasons, prescribed burning should be undertaken very carefully. The best time to treat depends on the method being used. If you can control seed production, you can control YST.

If you have YST, control measures should begin immediately, and will probably involve multiple methods and take time. Eradication cannot be accomplished with a single treatment, or in a single year. Effective management requires control of the current population and suppression of seed production - combined with establishment of competitive vegetation.

A valuable online resource can be found at cecentralsierra.ucanr.edu/files/87468.pdf discussing the management for Yellow Star Thistle in El Dorado County. Color photos of all stages of this plant and its seeds are on the beginning pages of this important 16-page document.

On Saturday, September 22nd, Master Gardener Steve Savage will present a FREE public education class on the “Starthistle” at the Government Center, Bldg C – Hearing Room at 2850 Fairlane Ct, Placerville from 9:00 a.m. to noon. The origins of this invasive weed, why it is such a threat, along with how to do battle will be examined.

UCCE Master Gardeners of El Dorado County are available to answer home gardening questions Tuesday through Friday, 9:00 a.m. to noon, by calling (530) 621-5512. Walk-ins are welcome at our office, located at 311 Fair Lane in Placerville. Visit us at the Sherwood Demonstration Garden, located at 6699 Campus Drive in Placerville, behind Folsom Lake College – El Dorado Center. The garden is open Fridays and Saturdays, 9:00 a.m. to noon.

For more information about our public education classes and activities, go to our UCCE Master Gardeners of El Dorado County website at  http://mgeldorado.ucanr.edu. Sign up to receive our online notices and e-newsletter at http://ucanr.edu/master gardener e-news. You can also find us on Facebook


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