Battle to Eradicate Hydrilla Continues

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Tompkins Weekly— May 19, 2012

By Sharon Anderson

As the waters of Cayuga Inlet warm, the tubers of an aggressive water weed known as hydrilla will sprout.  A volunteer aboard the Floating Classroom, Jordon Stark, found hydrilla (Hydrilla verticillata) in Cayuga Inlet in August 2011. It was the first confirmed occurrence of this pest in the entire Great Lakes basin. When found, this non-native plant already was present in more than 100 acres, with 9 acres of dense growth, even though it had been in our waters less than two years.  The exponential growth, up to a foot a day, means hydrilla could blanket the Inlet completely and spread to Cayuga Lake.

Boats – power, sail, windsurfer, canoe or kayak – can break off and carry fragments of the plant to new areas. The fragment then can sprout and form a new infestation.  Most likely the weed arrived here on a boat, trailer or fishing equipment from somewhere further south, such as the Potomac River. Hydrilla, which is native to India and other parts of Southeast Asia, has been in the United States for about 50 years.

Homes and businesses along Cayuga Inlet provide two million dollars in property taxes each year. Another two million dollars in revenue is generated by local businesses tied to boating in the Inlet and lake.  Much of that revenue will be lost if this non-native plant takes over.  If left alone, there would be a necklace of hydrilla choking Cayuga Lake everywhere the water is 20 feet deep or shallower.

The dense mats of hydrilla smother native vegetation and are poor quality habitat for fish. Not much else will grow once hydrilla takes over. The exception is blue green algae, which produces a neurotoxin blamed in the deaths of eight eagles in areas of North Carolina with hydrilla. Southern states and California have battled the noxious weed for years.  Florida has given up, spending millions of dollars each year to keep boat channels open by using mechanical harvesters and periodic herbicide treatments.  California has successfully eradiated hydrilla in many of its lakes.  Herbicide treatments are the only technique to successfully rid large, connected waterbodies of hydrilla.

After reviewing all the available options, the Cayuga Inlet Hydrilla Task Force has settled on herbicide treatment in Cayuga Inlet. The Task Force includes scientists, water quality professionals, elected officials and municipal staff and staff from regulatory agencies.  The first treatment, in October 2011, was successful. Ninety percent of the plant leaf and stem mass was killed.  However, the only herbicide feasible to use that late in the growing season did not kill the underground tubers, which look like miniature potatoes. Tubers over winter from year to year and, like stem fragments, can spread and start new plants.

“We’ve found it early and have the potential to stop it here, before it becomes an ecological emergency of the highest order.” says Roxanna Johnston, Watershed Coordinator for the City of Ithaca. “We know it will take years to eradicate hydrilla totally, but this was an important first step.”
Future herbicide treatments are planned starting as soon as the plant begins actively growing in the Inlet.  Additional herbicide treatment has been proposed for mid-summer to attack the underground tubers.  Similar herbicide applications will need to be repeated annually, probably until 2020, to completely eradicate hydrilla.

The herbicide used last fall, endothal, is expected to be applied in early summer, approximately mid-June.  The exact timing is based upon when the plant is actively growing and begins to form rhizomes.  The Inlet will need to be closed to boating and water recreation for one to two days but, if all goes according to plan, no longer.  The chemical treatment disrupts plant photosynthesis; the ability to make food from sunlight.  It is considered safe for other aquatic life, birds and human contact.  The Tompkins County Department of Health, in cooperation with NYS Department of Environmental Conservation, will monitor the levels of chemical in the water to ensure that the levels are safe.

“Eradication is always cheaper than maintenance,” says Johnston. “Eradication is only possible if you catch infestations early. Successful eradication requires early detection and a commitment to the treatment process both in funding and duration. Taking shortcuts with hydrilla treatment is not an option,” she adds.

For more information on hydrilla, visit or contact Sharon Anderson 607-272-2292 or

Sharon Anderson is the Environment Program Leader for Cooperative Extension of Tompkins County and serves as the chair for the outreach subcommittee of the Cayuga Inlet Hydrilla Task Force.

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