Its purple flowers look innocent enough but purple loosestrife is silently killing thousands of Midwestern waterways and wetlands.

This invasive weed offers no value to wildlife, interrupts fishing due to its thick plant growth above and below the water's surface and chokes out native vegetation.

University of Nebraska Weed Scientist Stevan Knezevic is studying integrated management approaches to stop this noxious weed's spread, including mowing, disking, biocontrols and herbicides.

A combination of herbicides and introducing loosestrife's natural enemy, the galerucella beetle, is the most effective approach, Knezevic's research shows.

Adult and larval galerucella beetles, introduced in the United States about 30 years ago, defoliate loosestrife. These insects, in combination with other plant species, act as natural competitors controlling loosestrife in its native Europe. The beetle is host specific and doesn't attack other plants.

Knezevic said birds eat the beetles, some beetles don't survive Nebraska's cold winters and the defoliation process is very slow.

"Bug control is only a small part to an integrated approach," Knezevic said. "It takes a couple hundred beetles to do some serious damage to a plant."

Herbicides also effectively treat larger loosestrife infestations, but few are available for use in wetlands. Since purple loosestrife is a perennial, spraying once doesn't kill it. Usually it takes two or three treatments over two or three years, he said.

Knezevic, who is based at NU's Northeast Research and Extension Center, works with county weed superintendents to gather and assess information to find the best integrated approach for combating the weed.

"I don't think that we can eliminate purple loosestrife completely," he said. "We have to find a way to live with it and reduce it to acceptable levels."

– Sandi S. Alswager

The color purple is bad news for wetlands. Purple loosestrife is a noxious weed that is choking out native plants and ruining wildlife habitat in wetlands and waterways.