Purple Loosestrife on the Loose

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Published on: Aug. 2, 1998

Last revision: Nov. 1, 2010

What's purple and green and can transform wetlands into wastelands? No, it's not Barney using his imagination again. It's purple loosestrife, a plant that has overrun hundreds of thousands of acres of North American wetlands, replacing a diverse vegetation of grasses, sedges and other wetland plants with a purple monoculture.

People choose purple loosestrife, a beautiful plant, as a landscape perennial to provide color during the heat of summer, when many horticultural species are not in flower, and to provide nectar for honeybees when other bee plants are scarce.

Despite its attractiveness, purple loosestrife provides little value to wildlife and can harm many wildlife species by completely dominating wetlands. Purple loosestrife habitats in Missouri include pond and lake edges, streambanks and ditches in pastures, fields and roadsides. Native wetland plants die out due to shading from the tall, dense purple loosestrife stands.

Native to Europe and Asia, purple loosestrife was first brought to North America in the early 1800s. Its seeds may have journeyed here accidentally in the ballast of ships or they may have been brought here intentionally for ornamental cultivation. Purple loosestrife has long been used as an herbal medicine to stop bleeding and treat dysentery, providing another motivation for intentional introduction. The seeds also may have hitched a ride in imported wool and when the wool was washed in this country the seeds entered our waterways. It now grows in nearly all of the lower 48 states and is most widespread in the northeastern and north-central United States and Canada.

Missouri had populations of purple loosestrife as early as 1952. The first reports came from Franklin and Newton counties. Today we find it in the wild at 45 sites in 23 counties. Macon County, in the vicinity of La Plata, is home to the greatest concentration of plants.

Like most problem exotic plants, purple loosestrife has the ability to spread rapidly once established in a wetland. A single plant may produce over 100,000 tiny seeds in a growing season. The seeds remain viable for long periods in wetlands and may be spread by wind, on the feet of waterfowl or by other wetland animals. Seeds become buoyant as they begin to germinate, allowing them to float to new areas.

Conservation Department land managers have been attempting to eradicate purple loosestrife since the late 1980s. A spray crew annually visits known sites in mid-summer and applies herbicide to the plants before they produce seeds. A

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