The Weed Society of America has given us plenty of bad news, but every now and then there's actually some good news to report. Listed on the "most noxious weeds" list in nearly three dozen states, purple loosestrife (Lythrum salicaria) has, at long last, met its match. First, let it be said that the stuff is actually rather pretty. With tall spikes of purple flowers that honey bees love, the plant hails from Europe, and there was a time when it was sold to gardeners across the U.S. Unfortunately, it's terribly invasive. The purple pest has choked waterways, displaced native aquatic plants, and affected wildlife and water quality across North America's temperate wetlands, and, considering that just one purple loosestrife plant can produce up to 2.5 million of its tiny, featherweight seeds, it's no wonder.

In the past, wetland managers have had limited success relying on the application of herbicides and hand-pulling before the weeds had a chance to go to seed, but, with a little help from two types of loosestrife-loving beetle, the numbers of the aggressive plants are withering. Some Minnesota-based researchers first enlisted the help of the beetles -- Galerucella calmariensis and Galerucella pusilla -- in the early '90s, and, since then, over eight million beetles have been released in that state. The result? Formerly lush stands of purple loosestrife look like rose bushes after a Japanese beetle convention. According to the Weed Science Society of America, the costs associated with herbicide management of purple loosestrife in Minnesota have decreased by tenfold from 1989 to 2003.

And Minnesota isn't the only state with a success story. Over the past decade, loosestrife infestations in the backwaters of Nebraska's Lewis and Clark Lake have been cut by nearly two-thirds, and any individual purple loosestrife plants that do manage to grow there -- despite the onslaught of hungry beetles -- have been badly stunted and very late to set seed. Overall, that means even less herbicide will be needed to control the weed, and, with any luck, maybe those wetland stewards will dispense with poisons altogether. 

This article originally appeared in "Plenty" in April 2008.

Copyright Environ Press 2008

Knocking back purple loosestrife
Beetles eliminate use of chemicals in invasive loosestrife battle.