Managing Cordova Creek: Staying ahead of Star Thistle

A native to Mediterranean Europe, the yellow star thistle (Centaurea solstitialis) made its way to California during the mid-19th century, likely via Chile through contaminated alfalfa mixes. With the lack of natural herbivores, the star thistle has the ability to create monotypic stands along disturbed landscapes. Their voracious nature eliminates and prevents other plants from growing, which degrades ecosystems and acts as a physical barrier for animal and human movement in wild spaces. Currently, it is estimated that star thistle occupies over 15 million acres of California’s floristic zone, and Cordova Creek, along with the American River Parkway, is no exception.

An unseasonably wet winter ‘16-17, hot summer, and the recently disturbed soil from Cordova Creek’s construction, all aligned to create an ideal habitat for star thistle to thrive in. As a result, the population exploded to an unprecedented level that the Water Forum and our partners were unprepared to fully manage. However, we are using the knowledge that we learned from last year’s experience to guide our current management strategies.

Starting in April, work crews have diligently hand-pulled and removed thousands of young star thistle growing throughout Cordova Creek. Despite their hard work, star thistle persistently exists in a few problem areas. To help address these problem areas, the Cordova Recreation & Park District,  Soil Born Farms, and the American River Flood Control District kindly agreed to each donate a day of mowing at Cordova Creek. Mowing star thistle can be extremely effective as a removal technique if timed correctly – once the plants have matured, bolted, and are at ~10% flowering. Mowing during this critical period prevents seeds from developing, and, without rain, the plants will be unable to regrow and flower this season.

We appreciate the help of Cordova Parks and Recreation, Soil Born Farms, and the American River Flood Control District as we manage and control star thistle. We are confident that the combined efforts will ensure the success of Cordova Creek and the immense amount of ecosystem services that it provides to the community!

For more information on how to manage star thistle in your own area: Yellow Star Thistle Management Guide

PostedFriday, June 22nd, 2018