Lythrum salicaria L. (Family: Lythraceae)

Description: Purple loosestrife is a perennial, emergent aquatic plant that can reach between 4 and 10 feet tall with up to 50 erect, annual stems growing from a single rootstock. Its stalkless, ½-inch- to 4-inch-long leaves are opposite, or sometimes in whorls of 3 on the lower part of the plant, and are rounded or heart-shaped at the base. Stems are 4- to 6-sided with evenly spaced nodes. The plant is covered in fine hairs. Pink-to-magenta flowers with 5 to 7 petals occur from June to September along 4- to 16-inch flowering spikes. The fruits are capsules that remain on the plant from October through winter.

Origin: Purple loosestrife is native to much of Europe and Asia. It was introduced to the United States and Canada in the 1800s for ornamental and medicinal purposes. It is still widely sold as an ornamental although its sale and purchase are illegal in several states including Indiana.

Distribution: Purple loosestrife invades many types of wetlands including wet meadows, tidal and non-tidal marshes, stream banks, pond edges, reservoirs, and ditches. It can sometimes grow in upland sites.

Problem: Purple loosestrife produces seeds prolifically—a single plant may produce 2.7 million seeds in a season—allowing the establishment of dense stands in only a few years. It excludes native vegetation and comes to dominate its wetland environment but is of little use to most native wildlife. Seeds are spread by water, by wind, and by clinging to animals. They remain viable for 10 to 15 years, and, once germinated, can reach sexual maturity in 8 to 10 weeks, flowering and reproducing in the same season. This leads to a very extensive seed bank.

Control: If plants are young, hand pulling or cutting during the summer is the simplest method for controlling purple loosestrife. If plants are older, be sure to remove as much of the root system as possible. If using chemical control, apply a 1.5-3% a.i. solution of glyphosate formulated for use over water during July or August. Broadcast spraying is not recommended. After spraying, any flower heads should be cut and removed.

USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations.

For more information, see http://www.invasive.org/species/weeds.cfm.

Photo credits:

• Steve Dewey, Utah State University, Bugwood.org, Image Number: UGA1459315
• Norman E. Rees, USDA Agricultural Research Service, Bugwood.org, Image Number: UGA0024065
• Linda Wilson, University of Idaho, Bugwood.org, Image Number: UGA1291004
• John D. Byrd, Mississippi State University, Bugwood.org, Image Number:  UGA1391156
• Steve Dewey, Utah State University, Bugwood.org, Image Number: UGA1459325
• Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, Image Number: UGA5273004