Yellow Starthistle

The Yellow Starthistle (Centaurea solstitialis Linnaeus), or YST is an invasive, alien plant, a noxious weed, brought from Europe and Asia over one hundred years ago, probably in grain and seed shipments.  It has gained a foothold in vast areas of the West.  Reports have it that YST extends over 10  to 15 million acres in California alone. On Skyline, under favorable conditions, it can over-winter and pop up already now, gold-feathered flower-head and crown of thorns!  It forms dense infestations and rapidly depletes soil moisture with taproots that can extend over three feet into the soil.  YST poses a threat to horses—if and when they eat great quantities of it over an extended period of time, causing “chewing disease” (nigropallidal encephalomalacia), a neurological disorder.  By the time the horse shows symptoms, the disease is fatal.

Yellow Starthistle flourishes here in the absence of natural controls. USDA research laboratories and scientists at U.C. Davis among others, with Joe di Tomaso in the lead,  have been carrying out studies in methods of eradication: chemical control with Transline and Roundup  and other herbicides as well as with bio-controls using several insect species, amongst them the False Peacock fly,  Chaetorellia succinea and two seed head weevils:  Bangasternus orientalis Capiomont and Hairy weevil, Eustenopus villosus , which selectively eat the Starthistle’s crown of seeds—if found, if set out at the right time, if the weather is favorable, and if not devoured by their own predators.

Timely control is all-important.   Patience and persistence pay off.  Hand pulling while the infestation is still manageable has proven effective, but one should not expect that a single treatment in a single year would do the trick.  Effective management requires control of the current population by a combination of appropriate to the situation methods and at the appropriate time.  The goal is suppression of seed production, combined with establishment of competitive, desirable vegetation.  Also important is avoiding accidental import of YST seed in contaminated hay and mulch.  Certified weed-free hay for livestock and horses is worth the cost!

A detailed summary of YST control options, their advantages, risks, timing and best fit in strategic management planning is provided by the U.C. Davis Weed Research and Information Center Web site http://wric.ucdavis.edu/yst/manage/management17.html

For more information on the experimental methods used and results including  more recommendations for control, contact the Agricultural Commissioner of your county, and/or USDA - ARS Biological Control of Weeds Laboratory, Western Regional Research Center, 800 Buchanan Street, Albany, CA 94710.  Below are additional Web sites you may wish to consult ^[1].

~ Eva Blum