Invasiveness Ranking System for Non-Native Plants of Alaska

Known level of impact in natural areas (0–6) 3Common St. Johnswort invades grasslands and open forestsin California, Oregon, Washington, Idaho, and Montana. InIdaho, common St. Johnswort creates medium to dense standsin grasslands, replacing native vegetation. It has been establishedin cut and burned-over areas in Pinus ponderosa forests in Idaho(Tisdale et al. 1959). This weed forms large dense stands in moistgrasslands and open forest areas in British Columbia (Powellet al. 1994, White et al. 1993). Common St. Johnswort invadeslarge areas in forests, riverbanks, and pastures in NortheasternAustralia (Parsons 1957)Role of anthropogenic and natural disturbance in3establishment (0–5)Original infestations are usually associated with logging, fire,mining, or other disturbance. It can establish in forested areasexperiencing natural disturbances such as fire or animal diggingand burrowing (Clark 1953, Davey 1919). Vegetative propagationis usually stimulated when St. Johnswort plants are affected bygrazing, mowing, or fire (Tisdale et al. 1959).Current global distribution (0–5) 3Common St. Johnswort is native to Europe, and it is naturalizedin Asia, South Africa, Japan, North and South America, Australia,and New Zealand (Gubanov et al. 2003, USDA, ARS 2005).Extent of the species U.S. range and/or occurrence offormal state or provincial listing (0–5)Common St. Johnswort has been found in nearly all thecontinental United States and Hawaii. It is known from BritishColumbia, Ontario, Manitoba, and Quebec (Crompton et al.1988, USDA 2002). Hypericum perforatum is declared a noxiousweed in California, Colorado, Montana, Nevada, Oregon,Washington, Wyoming, Manitoba, and Quebec (InvadersDatabase System 2003, USDA 2002).Total for Ecological Amplitude and Distribution 18/255Feasibility of ControlScoreSeed banks (0–3) 3In Australia, Clark (1953) found that St. Johnswort seeds mayremain viable in the soil for as long as 6 years. In Idaho, seedburied in soil retained viability after 3 years (Tisdale et al. 1959).Vegetative regeneration (0–3) 2Common St. Johnswort can sprout from buds on lateral roots(Rutledge and McLendon 1996).Level of effort required (0–4) 3Common St. Johnswort is difficult to control because of itsextensive root system and long-lived seeds. Tillage, hand pulling,mowing, or burning appears to be ineffective because vegetativereproduction may be stimulated by mechanical treatment(Tisdale et al. 1959). Common St. Johnswort can be controlledby herbicides, however, wax on the leaves inhibit herbicideuptake. Biological control has been relatively successful usingseveral leaf-feeding beetles. However, in Canada and at highelevations these insects do not thrive (Rutledge and McLendon1996, White et al. 1994).Total for Feasibility of Control 8/10Total score for 4 sections 52/100§B-56