The Biology of Invasive Alien Plants in Canada. 8. Lepidium latifolium L.

Abstract

The cruciferous weed Lepidium latifolium, perennial pepper-grass, is a relatively recent immigrant with a disjunct distribution in North America. Although first reported in the 1930s in Quebec and 1940s in Alberta, L. latifolium only started to attract attention as an invasive weed when it began to spread rapidly in the western parts of its US range in the 1980s, reaching British Columbia in the 1990s. Lepidium latifolium is a perennial weed of coastal wetlands, inland waterways, irrigation ditches, rangeland, hay meadows and waste areas, and tolerates saline/alkaline environments. Prolific seed production, rapid and substantial vegetative growth, creeping rhizomes with high storage capacity, potential for bud production at each node, and deep rhizome penetration have contributed to the widespread establishment of L. latifolium. Canopy height and density, combined with an accumulation of dead stalks in wetlands, has interfered with the regeneration of native plants and the habitats of birds and other animals, as well as hampering control of mosquitoes. In rangelands and pastures, L. latifolium can compete with native species and reduce forage quality. Lepidium latifolium has recently invaded agricultural crops such as cereal grains and alfalfa, and can contaminate hay shipments. Decaying litter may increase sodium content in surface soil, with a potential negative impact on salt-intolerant species. Lepidium latifolium has few natural enemies in North America. It has been partially controlled by flooding, intensive grazing, mowing and herbicides, but herbicides are of restricted use along waterways and in areas with native vegetation. Potential biological controls have shown little promise to date. Key words: Lepidium latifolium, perennial pepper-grass, perennial pepperweed, lépidie à feuilles larges, LEPLA, weed biology, invasive alien