Too close for comfort: Hydrilla hunting now urgent

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

The invasive plant Hydrilla verticillata has been confirmed in a lake less than an hour’s drive from Michigan. As a result, Michigan Sea Grant is encouraging waterfront property owners, boaters, anglers and swimmers to search the state’s inland lakes to make sure it hasn’t infested bodies of water in Michigan. Sea Grant is also asking recreational users to take precautions against transporting hydrilla and other aquatic invasive species on their gear.

Biologists from the U.S. Army Corps of Engineers recently confirmed the presence of the so-called “perfect weed” in Lake Manitou near Rochester, Indiana, 55 miles south of the Michigan border near U.S. 131, a major highway to the state.

Carol Swinehart, aquatic invasive species communication specialist for Michigan Sea Grant Extension, says it’s critical to find out whether any Michigan inland lakes are infested.

“The sooner we learn whether Michigan waters are infested, the better chance we have of eradicating or controlling it,” she says. “Many of our lakes are already infested with invasive Eurasian water milfoil, and experts tell us that hydrilla is even worse.”

Hydrilla has many adaptive qualities that allow it to outcompete and greatly diminish populations of native species. It can grow in low-light areas. It absorbs carbon from the water more efficiently than other plants. It is very tolerant to both standing and flowing water and can also grow up to an inch per day. Finally, its reproductive abilities make it particularly threatening. The tubers that grow from the 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.

Michigan Sea Grant Extension has spearheaded the Michigan Hydrilla Hunt since 2004 in collaboration with the Michigan Department of Environmental Quality Office of the Great Lakes. Background information and a specimen identification card are available through the Sea Grant Web site:

Citizens can also obtain hydrilla indentification cards and a fact sheet from Michigan Sea Grant Extension offices at Michigan State University and in Grand Haven, Traverse City, Tawas City, Mt. Clemens, Detroit and Marquette, as well as MSU Extension offices in Barry, Benzie, Branch, Calhoun, Charlevoix, Clinton, Emmet, Genesee, Grand Traverse, Livingston, Macomb, Montcalm, Muskegon, Kent, VanBuren, Kalamazoo and Ottawa counties and the Kellogg Biological Station in Hickory Corners.

“If someone thinks they’ve found hydrilla, we ask that they compare the plant with the image on our web site or the Hydrilla Hunt card, which provides illustrations to help distinguish it from the native aquatic plant elodea. If it has all the characteristics described there, send us a sample so that we can make sure,” Swinehart says.

It is illegal to possess hydrilla in Michigan (except to send it for identification) or to take the plant across state lines. Michigan residents and visitors can help prevent the spread of hydrilla by properly cleaning watercraft or other water recreation gear.
More information on invasive species prevention practices is available at

Michigan Sea Grant is a collaborative program of Michigan State University and the University of Michigan, conducting Great Lakes research, education and outreach. It is one of 30 Sea Grant programs in coastal states supported by the National Sea Grant College Program of the National Oceanic and Atmospheric Administration (NOAA). For additional information about Michigan Sea Grant, visit

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