Chemical

Chemical control tends to be the first control option most people utilize. There are many chemicals available that selectively control Yellow Starthistle. The table to the right is taken from Yellow Starthistle Management Guide.

A landowner should check with their local agricultural commissioner’s office on which application is approved for the target weed. In some cases, permits are required to use chemical control.

Chemical control can be an important component of an integrated approach. Research demonstrated a controlled burn in year one and a chemical treatment in year two was very successful at controlling YST. For more information you can read Integrating prescribed burning and clopyralid for the management of yellow starthistle.

Common name	Trade name	Registered in California	Mode of action	Weed Spectrum	Soil residual	Effective timing
2,4-D	Weedar®, Weedone® and many others	Yes	Growth regulator	Broadleaf species	Less than 2 weeks	Postemergence only, from seedling to bolting
Aminopyralid	MilestoneTM	Yes, in 2006	Growth regulator	Certain broadleaf families (between clopyralid and picloram)	Full season	Effective both pre- and postemergence; applied fall, winter or spring
Chlorsulfuron	Telar®	Yes	Amino acid synthesis inhibitor	Mainly broadleaf species	At least 2 months	Preemergence only
Clopyralid	Transline®	Yes	Growth regulator	Certain broadleaf families (e.g., Apiaceae, Asteraceae, Fabaceae, Polygonaceae, Solanaceae)	Most of the season	Effective both pre- and postemergence; applied fall, winter or spring
Dicamba	Banvel®, Vanquish®	Yes	Growth regulator	Broadleaf species	Less than 1 month	Postemergence only, from seedling to bolting
Glyphosate	Roundup®, and others	Yes	Amino acid synthesis inhibitor	Non-selective	None	Postemergence only, from seedling to early flowering
Imazapyr	Stalker®, Chopper®, Arsenal®, Habitat® (for aquatic use only)	Yes; not in rangelands	Amino acid synthesis inhibitor	Non-selective	Full season	Mainly as a preemergence treatment, postemergence control with seedlings or rosettes
Metsulfuron	Escort®	No	Amino acid synthesis inhibitor	Broadleaf species	At least 2 months	Fairly effective; preemergence only
Picloram	TordonTM	No	Growth regulator	Broadleaf species, weak on mustards	Up to 3 years	Effective both pre- and postemergence; applied fall, winter or spring
Triclopyr	Garlon®, Remedy®	Yes	Growth regulator	Broadleaf species	Less than 1 month	Postemergence only, good on seedlings, fair on mature plants

chemical YST

Control of YST on the left, untreated on the right.