Purple Loosestrife


Purple Loosestrife, Lythrum salicaria, is a large perennial wetland plant which is native to Europe and was introduced to the North America as an ornamental and medicinal plant in the 1800s. Purple Loosestrife can be found throughout 9 Canadian provinces and in nearly every state in the United States excluding Florida, Hawaii, and Alaska.
Distinct characteristics of this weed are its tall square stems which can grow up to 9ft. in height with 2-5 inch narrow leaves with a rounded or heart shaped base, and numerous off-shooting branches which in mature plants will bare bright purple inflorescence.

Purple Loosestrife seeds begin to germinate in moist or wet soil in the late spring and early summer when soil temperatures reach approximately 68°F. In the first season of growth alone the young plants can quickly grow up to 3ft tall, and generate a substantial taproot and root system which is used for nutrient storage. The plant will begin producing flowers in mid-June or July; seeds of Purple Loosestrife are easily spread through waterways, by humans and wildlife, as well as wind. When the first frost occurs in the fall the stems will die back and in the following spring new stems will be produced using the stored nutrients from the taproot.


Purple Loosestrife can grow in most wetlands and waterways including swamps, riverbanks, and ponds and it can quickly out grow native plants.

Biological Control

Four insects have been approved as biological control agents against Purple Loosestrife, Galerucella pusilla, Galerucella calmariensis, Hylobius tranversovittatus Goeze,Nanophyes marmoratus Goeze, in the Northeast primarily G. pusilla has been used.
G. pusilla beetle between 0.15 and 0.3 inches in length and light brown in color. The beetles emerge as adults from overwintering sites in the plant litter in the early spring. The beetles will feed for 8-10 weeks before mating in late May and early June. Feeding occurs on the leaves and young shoots, and eggs are laid on leaves and stems in clusters of 1-10 and covered in a black line of frass (fecal deposits). A single female is capable of producing up to 400 eggs in her life time. After about 1 week the larvae will hatch from the eggs and begin feeding on leaves and young shoots before pupating in the soil and emerging in mid-June and mid-July. These newly emerged adults will feed for a period before going down into the leaf winter to overwinter.
Biological control agents can have a substantial impact on the growth habitat of this plant. Purple loosestrife would normally grow to a height of 20 feet tall or more it only grows to 3 to 4 feet tall in the presence of the control organisms.


Reestablishment of Native Plants in Roger Williams Park Zoo Wetland after Biological Control of Purple Loosestrife, Lythrum salicaria