BACKGROUND: St. Johnswort was introduced from Europe. It invades areas with sandy or gravelly soils. Reproduction is by seeds and short runners. It contains a substance that is toxic (but rarely fatal) to white-haired animals causing them to develop skin irritations and often lose weight when exposed to sunlight. It is also a key ingredient of some popular dietary supplements.
Other common names: Klamath weed
DESCRIPTION: This perennial grows one to three feet tall. Stems are rust colored and woody at the base. Leaves are characterized by prominent veins and transparent dots, visible when held up to light. The flowers are bright yellow with five petals.
CONTROL: Several biocontrol agents are available and can offer good to excellent control. Herbicides can offer good control when applied to activley growing plants between rosette and pre-bloom stages. Contact your local state or county weed specialist for specific updated information.
Photos and text taken from Noxious Weed Field Guide for Utah
