Bill Johnson

Purple Loosestrife

Lythrum salicaria L.
Loosestrife family (Lythraceae)

Origin: Eurasia

Background
Purple loosestrife was introduced to the northeastern United States and Canada in the 1800s for ornamental and medicinal uses. It is still widely sold as an ornamental, except in states such as Minnesota, Wisconsin and Illinois where regulations now prohibit its sale, purchase and distribution. Purple loosestrife adapts readily to natural and disturbed wetlands.

Distribution and Habitat
According to the U.S. Fish and Wildlife Service, purple loosestrife now occurs in every state except Florida. It is found in many types of wetlands, including wet freshwater meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs and ditches.

Ecological Threat
Under favorable conditions, purple loosestrife is able to rapidly establish and replace native vegetation with a dense, homogeneous stand that reduces local biodiversity, endangers rare species and provides little value to wildlife.

Description and Biology

• Plant: erect perennial herb with a square, woody stem usually covered by downy hair; 4-10 ft. high, depending upon conditions.
• Leaves: lance-shaped, stalk-less and rounded to heart-shaped at the base; arranged in pairs or whorls around the stem.
• Flowers, fruits and seeds: produces a showy display of magenta-colored flower spikes throughout much of the summer. Individual flowers have five to seven petals. A single mature plant can have 30-50 stems arising from one rootstock, and can produce an estimated two to three million seeds per year. The flowering season extends from June to September; flowers require pollination by insects, for which they supply an abundant source of nectar.
• Spreads: through the vast quantity of seeds, dispersed by wind and water. It also readily reproduces vegetatively through underground stems at a rate of about one foot per year.
• Look-alikes: from a distance, purple loosestrife may be confused with blue vervain (Verbena hastata), blazing star (Liatris aspera and L. spicata), Canada germander (Teucrium canadense), swamp milkweed (Asclepias incarnata), and fireweed (Chamaenerion angustifolium), which is native to the northern U.S. and Canada.

Bill Johnson

Prevention and Control
Small infestations of young purple loosestrife plants may be pulled by hand, preferably before seed set. For older plants, spot treatment with a glyphosate-based herbicide such as Rodeo® for wetlands or near water and Roundup® for uplands may be effective (see Control Options). Biological control, using several imported beetle species approved by the USDA for release, is the most effective method for long-term control of large infestations.

Native Alternatives
Blazing star (Liatris aspera and L. spicata), blue vervain (Verbena hastata), Canada germander (Teucrium canadense), cardinal flower (Lobelia cardinalis) and ironweed (Vernonia noveboracensis).