Bear Valley Community Services District

Yellow Starthistle Identification and Management

Yellow Starthistle identification and management

Published on:
June 24, 2019
Originally published:

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 isout of control, wasting up to 15 million acres of range and farm land.  We do not want it to get any more out ofcontrol here.  This very invasive weed isunpleasant, as it has sharp needles around each  flower, which neither man nor beast would walkinto.  It will out-compete native andother invasive plants and weeds, as it has a very deep tap root.  It will suck the soil around it dry to adangerous extent, possibly affecting the water table.  Plants bolt and flower continuouslythroughout the summer months, requiring constant monitoring.  

Yellow Starthistle flowerhead

The BVCSD no longer has a Yellow Starthistle controlprogram, except on CSD-owned land and rights-of-way.  It is now necessary that the property ownerscontrol any YST on their land.  And it isrequired 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 YSTat all of its stages, so that you can recognize it at its earliest stages onyour property.  For the earlier YST isidentified, the easier it is to control.

Before flowers appear, the YST may be removed by cutting itoff at ground level—I find a shovelis 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 carefullydisposed of at the yellow starthistle burn area at the CSD green waste disposalarea.  I recommend accumulating it on atarp rather than trying to get the sticker-ie 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-emergentspray control.  Or YST can be sprayedwith a post-emergent such as 2,4-D (preferred) or Roundup.  

Mature Yellow Starthistle plant

Once any flowers erupt, a much strongerconcentration of the herbicide is required; and, when fully flowered, the plantcan no longer be effectively controlled by spraying. Never mow or weed-whackYST, as the stem will be left and it will simply re-grow closer to theground.  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 heavyflowering and for small infestations, cut it off at ground level with a shovelor hoe.  Then, if there are flowers,remove the plants carefully to the CSD burn pit located at the Solid Waste TransferStation.