St. John's Wort in Australia

Abstract

ST. JOHN'S WORT (Hypericum perforatum var. angustifolium), introduced into Australia in about 1880 as a garden plant, is now a serious weed in many parts of that country. Besides reducing the carrying capacity of the pasture, stock may become affected with 'wort dermatitis', for the hypericin in the plant acts on the nervous system, rendering the exposed non-pigmented areas of their skin photosensitive. Control measures of various kinds are being tried, including improvement of the pasture by sowing competitive species, chemical treatment and the liberation of insect parasites. Some account of the success attending these trials is given in recent publications of the Australian Council for Scientific and Industrial Research. Bulletin 151 consists of a paper by R. M. Moore and A. B. Cashmore, who have investigated the problem from the agrostologist's point of view, while the entomological aspect is specially dealt with by F. Wilson and T. G. Campbell in the Council's Journal (16, p. 45). The results are most promising. Subterranean clover (Trifolium subterranean), a winter-growing annual, proved an efficient competitor with St. John's wort, and in association with perennial grasses, such as Phalaris tuberosa or Lolium perenne, almost completely eradicated the weed and provided a productive and nutritious pasture. The mixture is best sown with a dressing of superphosphate after a summer fallow, a dense pasture being afterwards maintained by regular top-dressings and a rotational system of grazing. The use of dark-coloured stock is also recommended as they are less prone to wort dermatitis. For entomological control, three insects have been established in Australia, two leaf-eaters, Chrysolina hyperici and C. gemellata, and a root-boring Buprestid, Agrilus hyperici. The prospects of success are good, particularly with Agrilus, as it is remarkably free from predators and parasites, but the Chrysolina species have a high reproductive rate, and judging from experience in France, all three insects can play a useful part in the control of the weed.