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Purple loosestrife is a perennial, herbaceous plant with one to 50 square stems that give the plant a bushy appearance. Its leaves are opposite or whorled, lance-like and rounded at the base. The plant flowers from June to September and its flowers are magenta with five to seven petals each.

This plant was introduced from Europe and Asia to the northeastern U.S. and Canada in the 1800s for ornamental and medicinal uses. Purple loosestrife is capable of invading wetlands such as meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs and ditches. A mature plant may produce two to three million very small seeds per year and the seeds can remain viable for 20 years. It also reproduces through underground rhizomes at a rate of about one foot per year.

Purple loosestrife adapts to natural and disturbed wetlands where it replaces native grasses, sedges, and other flowering plants that provide more nutrition for wildlife. Its dense, homogeneous stands restrict native wetland plant species and reduce habitat for waterfowl.

Small infestations of young plants may be pulled by hand, preferably before seed set. For older plants, spot treatment with an herbicide may be most effective when applied in mid-summer and again late in the season. Three insects have been approved by the USDA as biological controls.
More Resources:

Biological Control of Purple Loosestrife
Plant Conservation Alliance
Southeast Exotic Pest Plant Manual
Element Stewardship Abstract

Plant Invaders of Mid-Atlantic Natural Areas
U.S. Forest Service
Invasive Plants
Pennsylvania State University

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