Contact: Kerrie L. Kyde, Habitat Ecologist/Invasive Plant Specialist, Maryland DNR | kerrie.kyde@maryland.gov
ANNAPOLIS, MD (July 7, 2006) – In the tradition of enticing but scary summer horror movies, Maryland’s wetlands could soon be putting on a beautiful but insidious summer show, starring the European invader purple loosestrife. This moisture-loving plant, sporting long spikes of magenta blossoms, spreads prolifically by seed and can crowd and shade out the native plants normally found in our marshes. Although some bees visit purple loosestrife, it doesn’t provide the same food and shelter to wetland animals as the native mixed wetland community of cattails, sedges, rushes and grasses. Because during this month it is easily visible in wet places, and because Maryland DNR has a control program targeting this plant, MISC has named purple loosestrife July’s Invader of the Month.
Purple loosestrife (Lythrum salicaria) is a tall, branching perennial herb that grows in sunny moist or marshy areas. At bloom time, in July and August, it can be as much as 8’ tall. The purple-pink flowers appear in dense spikes at the top of the plant. Each flower usually has 6 petals (sometimes 5 or 7) and yellow-white centers. The leaves are opposite – two at each joint on the stem – and attach directly to the stem. They are long and narrow, with pointed tips and smooth edges. The stems of purple loosestrife are squared off and fuzzy. You can feel the edges if you try to roll the stem between your finger and thumb. Later, after the flowers are gone, the seeds mature – as many as 2 million per mature plant – in small golden brown capsules with 6 pointed tips.
Purple loosestrife was accidentally introduced into the eastern US in the early 1800s in discarded ballast water from ships trading with Europe. Later, it was brought deliberately for both medicinal and ornamental purposes. It spreads primarily by seeds, which can remain viable in water even after 2 years. The rootstocks and stems are semi-woody and remain standing in the winter after the plant has finished producing flowers and seeds. Although it does not spread widely vegetatively, new plants can sprout from broken pieces of rootstock moved around by water.
Purple loosestrife can modify marshes in several ways. It can reproduce and spread to form huge colonies called “monocultures” in which it is virtually the only plant present, suppressing native seedlings and reducing biodiversity. In turn, this monoculture reduces food, pollen and shelter sources for wetland animals, including endangered species such as the sora, American bittern and bog turtle. Growth of the plant’s rootstalk, and the debris that collects around the base of the stem can change the level of the soil surface and thus redirect water flow in marshes, roadside ditches and stormwater management ponds.
Mechanical, chemical and biological methods of control work on purple loosestrife. The plant can be dug or grubbed out by hand, but you must be careful to get all the roots. Foliar sprays of 2% glyphosate – the formula approved for use near water – can effectively kill the plant. And a beetle named Galerucella pusilla, which eats only purple loosestrife, can reduce populations to below the threshold level of ecological damage. The Department of Natural Resources is teaching MD citizens of all ages to recognize and report populations of this plant, so that they can be removed before purple loosestrife causes irreparable harm to Chesapeake Bay marshes. Find out how you can help at: http://www.dnr.state.md.us/wildlife/Plants_Wildlife/PurpleLoosestrife/. For more information about the Loosestrife Scout project and about this plant, please contact Kerrie Kyde at DNR.
For more information about other Invasive Species of Concern, visit the Maryland Invasive Species Council.