Growth habits and impact on wetlands. Purple loosestrife forms a woody crown from which it sends up new shoots each year. The old stems often stay erect and in dense stands prevent light from penetrating to the soil surface effectively reducing competition by native species. In a loosestrife infested wetland, the erect dead stems restrict access to open water by resident and migratory waterfowl. Although there has been little research documenting reduction in waterfowl numbers in loosestrife infested wetlands, there is agreement among many research scientists and wildlife managers that purple loosestrife does reduce the quality of wildlife habitat.
Seed is the primary means of dispersal.
Seed is exceedingly small and dispersal is by moving water or by transport of contaminated soil as it clings to motor vehicles and animals as they move through a loosestrife infested wetland. A single plant that is left uncontrolled poses a significant threat to any wetland. Conventional control practices range from herbicides to hand removal of plants and manipulation of water levels. In large infestations where purple loosestrife has formed dense monotypic stands, or where the extent of the infestation covers large areas with purple loosestrife at low to moderate density, conventional control is far less effective and suppression rarely lasts for more than a few growing seasons. In general, using nonselective herbicides in large expanses of purple loosestrife is not recommended.