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Exotic invaders
 by Rebecca Goetz
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Purple loosestrife, also known as "purple plague," has spread throughout the United States, invading lowlands and marshes. (photo courtesy Carole Lembi) |
Plants are some of the worst invaders along the Great Lakes, Charlebois says.
Purple loosestrife, for example, has invaded so many U.S. lowlands and marshes that it's earned the nickname "purple plague." This native European plant arrived in the 1800s, when New Englanders so admired its flowers that they planted it in gardens. From their flowerbeds, it spread through most of the United States.
"When purple loosestrife comes in, it takes over," Charlebois says. "It pushes everything else out. And animals don't use it. The plant's seeds are even too small for birds to eat."
In the spring, Charlebois and Natalie Carroll, state environmental 4-H specialist, taught volunteer 4-H leaders to raise loosestrife-eating beetles (also an exotic but one that doesn't harm the environment). The leaders, in turn, teach 4-H youth to release these beetles in marshes and lowlands infested with purple loosestrife; 4-Hers will watch the marshes to see if the beetles have any effect.
Another aquatic invader came to the Midwest in fish tanks. In the 1940s, people used Eurasian watermilfoil to brighten their aquariums. Soon after, the plants started showing up in U.S. waterwaysprobably dumped by people tired of feeding goldfish and scraping algae. Unknowingly, these former fishkeepers started a green revolution that has filled up lakes across the United States and Canada.
"Eurasian watermilfoil is a big pest in natural lakes in northeastern Indiana," says Purdue aquatic weed scientist Carole Lembi. "This thing grows 15 to 20 feet deep and crowds out native species of plants. It can really fill a lake and make it hard to swim. And it gets sucked up in boat motor intakes."
Homeowners can use herbicides to kill Eurasian watermilfoil, Lembi says, but some herbicides indiscriminately kill all plants in a lake. When all the plants die, fish and the creatures they feed on lose their habitat and cover from predators. Then, as the dead plants decompose, they can use up the oxygen in the water and cause a fish kill.
Lembi is looking at methods to control Eurasian watermilfoil that are better for the environment. She has been testing plant-growth regulators called gibberellin synthesis inhibitors. These compounds stunt Eurasian watermilfoil just enough to keep it out of boat motors, fishing lines and swimmers' feet.
From what she's seen in field tests, gibberellin synthesis inhibitors are effective on Eurasian watermilfoil and other aquatic weeds. She's hoping industry will pick up on it and make it commercially available.
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