The biology of invasive alien plants in Canada. 9. Impatiens glandulifera Royle

Abstract

Impatiens glandulifera Royle (Himalayan balsam) is an invasive alien annual up to 3 m in height with showy flowers that are generally pink or purplish. Native to the Himalayan region, I. glandulifera was first recorded in Canada in 1901 in Ottawa, and is now found in eight Canadian provinces: British Columbia, Manitoba, Ontario, Quebec, Nova Scotia, New Brunswick, Prince Edward Island and Newfoundland. Impatiens glandulifera is typically found in riparian habitats and may spread rapidly because its seeds are readily transported via waterways. Up to 2500 seeds are produced per plant and dispersed explosively up to 5 m from the parent plant. This can result in dense monotypic stands which prevent establishment of native plants and make stream banks vulnerable to erosion when the shallow-rooted plants die back. Impatiens glandulifera is susceptible to glyphosate but because herbicide use in riparian areas is not advised, other control methods such as hand weeding, mowing or flaming have been used. Methods for eradication are most successful when upstream populations are controlled first, as the plants spread downstream. Removal of I. glandulifera should be managed synchronously with non-native control measures and ideally be accompanied by planting native species to ensure the restoration of native species composition. The prognosis for curbing its spread in Canada seems poor as it has quite rapidly become established along waterways in many regions, following a pattern seen over the past two centuries in Europe. Key words: Impatiens glandulifera, Impatiens roylei, Himalayan balsam, impatiente glanduleuse, policeman's helmet riparian, invasive plant, weed biology