Bear Valley Community Services District

Yellow Starthistle Identification and Management

Yellow Starthistle identification and management

Published on:
June 24, 2019
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very obnoxious weed with a pretty name:  Yellow Starthistle (YST).  This scourge on the land of the western U.S.was discovered in the Tehachapi area and BVS in 1990 by Chuck McCollough (founderof Triassic Legacy Winery).    In Northern California yellow starthistle is out of control, wasting up to 15 million acres of range and farm land.  We do not want it to get any more out of control here.  This very invasive weed is unpleasant, as it has sharp needles around each  flower, which neither man nor beast would walk into.  It will out-compete native and other invasive plants and weeds, as it has a very deep tap root.  It will suck the soil around it dry to a dangerous extent, possibly affecting the water table.  Plants bolt and flower continuously throughout the summer months, requiring constant monitoring.  

Yellow Starthistle flowerhead

The BVCSD no longer has a Yellow Starthistle control program, except on CSD-owned land and rights-of-way.  It is now necessary that the property owners control any YST on their land.  And it is required by the CSD and BVSA that YST or any invasive weeds be removed.

I encourage you to go on the internet to see pictures of YST at all of its stages, so that you can recognize it at its earliest stages on your property.  For the earlier YST is identified, the easier it is to control.

Before flowers appear, the YST may be removed by cutting it off at ground level—I find a shovel is easier than a hoe to accomplish this. The plant may be left on the ground. However, once flowers (seed) are present, the plant must be carefully disposed of at the yellow starthistle burn area at the CSD green waste disposal area.  I recommend accumulating it on a tarp rather than trying to get the plant into a trash bag.  No plastic is to be dumped in the burn pit.

Young, pre-flower Yellow Starthistle Plant

Before many YST flowers appear, “Star Thirstle Killer” is aclopyradid herbicide product that is appropriate for both pre-and post-emergent spray control.  Or YST can be sprayed with a post-emergent such as 2,4-D (preferred) or Roundup.  

Mature Yellow Starthistle plant

Once any flowers erupt, a much stronger concentration of the herbicide is required; and, when fully flowered, the plant can no longer be effectively controlled by spraying. Never mow or weed-whack YST, as the stem will be left and it will simply re-grow closer to the ground.  And, if the plant is in flower,it will spread the seeds.

 

Again, before many flowers have appeared, spray with “StarThistle Killer” or 2,4-D.  After heavy flowering and for small infestations, cut it off at ground level with a shovel or hoe.  Then, if there are flowers,remove the plants carefully to the CSD burn pit located at the Solid Waste Transfer Station.