THE BIOLOGY OF CANADIAN WEEDS. 83. Hypericum perforatum L.

Abstract

Hypericum perforatum L., St. John’s-wort is an introduced weed growing in waste places, roadsides, rangelands, pastures and similar habitats of Eastern Canada and British Columbia. It is poisonous to livestock causing a photosensitization in grazing animals with light-colored hair. In Canada, two introduced leaf-feeding beetles Chrysolina quadrigemina and C. hyperici have provided effective control. In Nova Scotia an endemic host-specific "strain" of Colletotrichum gloeosporioides generally maintained this weed at low levels, particularly in lowbush blueberry fields. It spreads both by seeds and vegetatively by rhizomes. Details related to its morphology, reproductive biology, responses to human manipulation, parasites and control measures are summarized.Key words: Hypericum perforatum, weed biology, review