Seed set begins in mid to late July and continues through late summer. Seeds may be dispersed by water, wind and in mud attached to animals. Purple loosestrife also spreads vegetatively. Root or stem segments can form new flowering stems. Muskrat cuttings and mechanical clipping can also contribute to rapid spread by floating in riverine and lacustrine systems.
Purple loosestrife lacks natural enemies in the United States.
Purple loosestrife quickly crowds out most native vegetation in marsh, fen, sedge meadow, wet prairie, bog, and panne communities, creating a monoculture that provides little food or shelter for native wildlife. The natural character of several Illinois nature preserves is threatened by this exotic species. Current Status Purple loosestrife is categorized as an exotic weed under the Illinois Exotic Weed Control Act of 1987. As such, its commercial sale in Illinois is prohibited. However, only mechanical and chemical means of control are currently available.