Introduction:
Common St. John's wort (Hypericum perforatum) Weed.
Hypericum perforatum, more commonly known as St. John’s wort, is a native flowering perennial plant of Eurasia. It has been widely introduced, mainly by human vectors, to North and South America, parts of Africa, Australia and New Zealand. St. John’s wort can survive in a wide range of environments and has the ability to store reserves in its root crown and compensate during harsh times, which makes this plant difficult for management control. In recent years Hypericum perforatum has gained media attention for its use in alternative medicine, mainly for treating depression.
Description:
St. John’s wort is a perennial herb with two distinct growth phases, a fall/winter prostrate or basal growth, and a spring/summer erect woody stem growth. St. John’s wort has an underground rhizomatous stem and deep taproot with many lateral roots. The erect vegetative growth has opposite, sessile, entire, linear to elliptical leaves 10-30mm long and 3-16mm wide, with translucent glands located on the undersides of the leaf and black glands located along the leaf margins. The flowers are numerous, paniculate cymes with 5 yellow petals, 5-8mm long, black dotted along the margins as well. Multiple stamens cluster into three groups, with three styles present. The capsules are 7-8mm long, dark brown ovoid, three chambered, holding thousands of small, pitted cylindrical seeds.
Occurs in:
Agricultural areas, natural forests, planted forests, range/grasslands, ruderal/disturbed, scrub/shrublands, urban areas.
Common St. John's wort (Hypericum perforatum) Distribution in North America shown in green.
Habitat description:
Hypericum perforatum forms dense stands on recently disturbed sites from impacts like mining, fire, logging, construction, etc. It also establishes itself in waste grounds, roadsides, pasture, rangeland, and open woodland. It has adapted to a wide range of environmental conditions in its native and introduced range. H. perforatum can tolerate a variety of soils, from dry, rocky, shallow soils, to deep fertile soils, with it performing best in regions with greater than 760mm of precipitation a year. Soil pH tolerance ranges from 4.3-7.6. It can tolerate drought and disturbance conditions by storing reserves in its root crown.
General impacts:
St. John’s wort establishes itself on recently disturbed sites and displaces and inhibits the settlement and establishment of native flora. The plant contains two primary toxic compounds hypericin and hypericum red, which can cause photosensitivity in grazing livestock, leading to loss of weight and condition, even death in rare circumstances. The dried stems that are present during the fall and winter can pose as a fire hazard for forest and range lands.
Management information:
Chemical:Chemical control of St. John’s wort has had mixed results depending on the management plan and location of application. In South Africa, the initial
Close up of the Common St. John's wort (Hypericum perforatum) Weed.
management plan was a chemical eradication, however this programme was suspended when it proved unsuccessful and too expensive. Similarly, a chemical control in British Colombia, Canada, also was uneffective in eradicating the plant. However several field studies and programmes were initiated that designed a chemical application management strategy in the foothills and pasture lands of South Australia. Several different chemical formulations were used, but the ones that proved most successful were a combination of 2,4-D + 2,2,-DPA, or a straight application of glyphosate. Timing of the applications is crucial in the success of a chemical application, with an autumn spraying seeming to be most effective in Australia. In addition the method of application and the composition of the infested area prerequisite the chemical used. Triclopyr + picloram in combination were not selective for just St. John’s wort but also killed any nearby legumes. A boom and spot method for application was discovered to work best with these chemicals. For glyphosates an aerial application worked better, and was more selective to St. John’s wort, however glyphosates did not perform well at warmer temperatures. For the best coverage using an aerial application adjuvants, water carriers, and repetitive anuual sprayings are recommended. Ammonium sulfamate has been shown in several studies to be an effective herbicide against woody stem plants and St. John’s wort, with the added benefit of decomposing into a plant soluble fertilizer for native grasses.
Physical: Mechanical removal is not recommended for this species as it can vegetatively reproduce from the rhizomatous root crown which can be quite extensive underground. Fire is not recommended as a means of control since the plant can persist from underground resource storage in its crown and then reproduce through suckers.
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