Hydrilla: The ‘Perfect Weed’

Michigan waterfront property owners spend an estimated $20 million annually to control aquatic invasive plants, primarily Eurasian watermilfoil and curly leaf pondweed. That cost could increase dramatically, according to the Michigan Department of Environmental Quality (MDEQ), if the invasive plant hydrilla finds its way into Michigan waters.

In a presentation at the 2007 Great Lakes conference at Michigan State University, Eric Bacon of the MDEQ’s Water Bureau noted that Hydrilla verticillata has been confirmed in Indiana’s Lake Manitou, less than an hour’s drive from Michigan.

According to Bacon, the density of growth suggests that hydrilla has likely been there for a few years. In some places, its thick coverage along the lake bottom extends upward to within a few inches of the water’s surface. The dense monoculture appears to have suppressed other plant species in the same area.

Bacon and colleagues from the MDEQ visited the 700-acre lake in 2006 to examine hydrilla in natural conditions, gain experience in identification, and rehearse the agency’s response if the plant shows up in Michigan. Hydrilla is one of 11 aquatic invasive plant species listed as prohibited in Michigan.

The so-called “perfect weed,” hydrilla has several adaptive qualities that allow it to out-compete populations of native species. It tolerates both standing and flowing water and can grow up to an inch per day. It can grow in low light conditions and absorbs carbon from the water more efficiently than other plants, allowing it to grow where other aquatic plants cannot, such as in deeper water and in turbid conditions.

The tubers and runners that grow from the plant’s roots can persist, in a viable state, in the lake bottom for several years. It can also reproduce through flowers, fragments, and turions (cone shaped growths) on its stalks.Like other aquatic invasive plants, hydrilla spreads to new water bodies when fragments get tangled in boat motors and trailers. Waterfowl may also spread the plant by ingesting fragments and turions.

To aid in early identification of hydrilla, Michigan Sea Grant asks that Michigan citizens watch for hydrilla in water bodies this summer. Sea Grant has spearheaded a Michigan “Hydrilla Hunt” since 2004 in collaboration with the Michigan Department of Environmental Quality Office of the Great Lakes. A Hydrilla Hunt card, shown above, offers photos and additional information about the plant.

“If residents think they’ve found hydrilla, we ask that they compare the plant with the image on the Sea Grant web site or the Hydrilla Hunt card,” says Michigan Sea Grant’s Carol Swinehart. The images provide illustrations to help distinguish hydrilla from the native aquatic plant elodea.

> Next Article