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Purple Loosestrife: Colorful, Extremely Attractive -- and a Menace

September 15, 2009 - AUGUSTA -- Those eye-catching, tall, magenta-colored perennials growing near ditches, along lakes and in wetlands may be pretty enough for a fall wildflower bouquet.

Don't even think about it, say plant experts. The plant is among the most aggressive, invasive species to spread its seeds and roots in Maine.

Purple loosestrife was introduced from Europe into the United States and Canada in the 1800s for ornamental and medicinal uses. It is now growing throughout Great Britain, across central and southern Europe to Asia, China and India and in the United States, is considered to be an invasive species.

"It is quite adaptable and can live in climates from northern Ontario to Texas, and it has tremendous potential for reproduction," said Lois Stack, a horticulture specialist with the University of Maine Cooperative Extension.

Purple loosestrife is an erect perennial herb with a square, woody stem and lance-shaped, stalkless leaves. Plants grow 4 to 10 feet high and produce a showy display of purple flower spikes throughout much of the summer.

It is a very prolific seed-setter with a vigorous root system that stifles other plants and spreads at a rate of about a foot a year, according to the Cooperative Extension.

One rootstock alone can send up 30 flowering stems that produce up to 3 million minute seeds a year.

"The problem is that it is very aggressive in wetlands and out-competes and replaces native species like cattails and native grasses," Stack said."It is changing the whole system because it doesn't just co-exist. It takes over."

What is alarming is its adaptability. She said just in the past 10 years, she has seen it show up in areas that are drier than the plant normally thrives in.

"To have it change so rapidly is a concern," she said.

Waterfowl use cattails, sedge and native grasses for cover and as a source of nutrition. But when purple loosestrife moves in, it forms a dense, monoculture that pushes out floating vegetation by closing open water, she said.

The plants can be found along culverts and ditches and in wet spots. When the pods burst about this time of year, the seed falls to the ground and can be spread by moving water to lower ground, Stack said.

At this time of year and in the summer, small infestations can be curtailed if people carefully snip the base of the tall stalk and capture the flowers and pods in plastic bags. They should be disposed of in a landfill -- not in a compost pile, Stack said.

Hand-pulling plants can be done in small areas with proper gardening tools; but like invasives such as milfoil, even minute pieces of root left behind will develop into new growth, she said.

If the flowers have already gone by this late in the season, Stack suggests people make a mental note or mark the area to clip the plants earlier next year.

But those in the field are banking on biological control as the best long-term option, said state horticulturalist Ann Gibbs from the Maine Department of Environmental Protection.

As of 1997, the U.S. Department of Agriculture has approved three inspect species from Europe for use as biological control agents.

Two of them -- flower-eating Galerucella beetles that chomp on various parts of purple loosestrife -- have been released experimentally in areas in 16 northern states, including Maine, Gibbs said.

The experiments show the potential impact of the insects on nontarget species is low. The beetle does not eradicate purple loosestrife, but it keeps the plant under control, she said.

"I've been watching this plant for years, and as we have more development, it spreads," she said.

Studies have shown the species does well in wetland habitats that have been disturbed or where road work or building is going on.

"You can see it now all up and down I-95," Gibbs said.

For more information, visit the University of Maine Cooperative Extension at www.umext.maine.edu, click on "publications" at the top and type in "purple loosestrife" in the search box.

Kennebec Journal news story
Monday September 14th, 2009

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