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 www.mdinvasivesp.org or call the
Maryland Department of Agriculture at 410-841-5920.
photos available electronically on request.