St. John's wort: pest

Page last updated: Tuesday, 14 April 2020 - 1:58pm

Please note: This content may be out of date and is currently under review.

St. John's wort, klamathweed, goatweed (Hypericum perforatum) is a common weed in the lower southwest of Western Australia (WA). This article describes the nature of the plant with links to control methods.

Form: herbaceous — perennial

Status: present in WA

Appearance

Native of Europe, western Asia and North Africa. There are two varieties, var. perforatum with broad leaves and var. angustifolium with narrow leaves, but intermediates are also known. One plant will produce thousands of seeds and these may remain viable in the soil for many years. Introduced to Australia in 1800s, and still spreading, especially on roadsides and cleared land. St. John's wort can densely infest grazing land, particularly when pastures get denuded.

The leaves of St. John's wort contain a toxin which causes photosensitisation, especially amongst white-faced stock. The plant also affects animals nervous systems, causing unthriftiness and sometimes death.

St John's wort is a perennial plant that reproduces from seed and from creeping underground rhizomes. The plants do not flower in their first year, but flower and seed prolifically in later years. Seeds may survive in the soil up to six years before germination.

Stems: In winter the stems are spindly and low growing with a dense mat of leaves. Erect woody stems are produced in spring. These are cylindrical and shiny, often reddish,  0.6 to one metre tall, branching near the top with two opposite ridges running down the stem.

Leaves: 1.5 to 3 centimetres long and narrow, stalkless and arranged in opposite pairs. They bear translucent oil glands, which are clearly seen when held to the light.

Flowers: The flowers are up to 25 millimetres across with five bright yellow pointed petals, that often have black dots on the edges. There are three bundles of yellow stamens in each flower. Numerous flowers are found together in clusters near the top of the stems. Flowers in late spring and summer

Seeds: Dark brown to black, cylindrical and one millimetre long. They are produced in large numbers in a sticky capsule. Seeds germinate in either spring or autumn.

Agricultural and economic impact

Toxic to livestock.

Declared pest category

The Western Australian Organism List (WAOL) contains information on the area(s) in which this pest is declared and the control and keeping categories to which it has been assigned in Western Australia (WA). Use the external links on this page to reach St. John's wort in WAOL.

Search > detect > record

Record: this pest using the MyWeedWatcher smartphone and tablet application or online recording tool.

Control method

When using any agricultural chemicals please ensure that you always follow instructions on the label and any permit. Users of agricultural chemical products must always strictly comply with the directions on the label and the conditions of any permit.

Only registered products can be used for weed and pest control.

Control methods for this plant can be found through the APVMA website, use "wort" as the pest name.