Weed scientists warn of aggressive spread of hydrilla, spotted in N.Y.

LAWRENCE, Kan. — Six months ago one of the world’s most aggressive aquatic weeds was spotted in an inlet adjoining Cayuga Lake, part of New York’s famed Finger Lakes.

The culprit was hydrilla (hydrilla verticillata), an aquatic plant species holding a well-earned spot on the federal noxious weeds list. Officials fear an environmental disaster in the making — and for good reason. A native of Asia, hydrilla gained a toehold in the U.S. about a half century ago and has wreaked havoc since.

“Dense mats of vegetation can quickly take over a body of water, where they clog flood control channels, impair water supplies and endanger recreation and tourism,” said Robert Richardson, Ph.D., an aquatic weed specialist from North Carolina State University and a member of the Weed Science Society of America.

“A 15-acre infestation found in Florida spread to 3,000 acres in just two years — a tribute to hydrilla’s fast growth,” he said. “It can spread through creeping shoots, fragmented shoots and tubers. The tubers can remain dormant in sediment for years.”

Large waterway

Previous New York detections have been limited to small ponds or contained bodies of water. But the Finger Lakes discovery raises the stakes. Each lake is part of an interconnected waterway, creating the potential for hydrilla to spread, travel through the Erie Canal and contaminate the Great Lakes.

“We estimate this particular infestation approaching two years old, and it covers up to 166 acres,” said Roxanna Johnston, watershed coordinator for the city of Ithaca. “We’ve found it early and have the potential to stop it here, before it becomes an ecological emergency of the highest order.”

A coalition of state and local officials, university personnel and hydrilla experts from around the country quickly banded together to take action. They knew typical control methods used in a contained pond wouldn’t work in the inlet — such as draining the infested water, introducing grass carp to feed on the hydrilla or using matting to smother the plants.

Harvesting by hand was attempted, but the murkiness of the water made for difficult working conditions. In addition, the hydrilla fragmented during harvesting, and officials worried that small particles floating away might actually serve to spread the plant.

In the end, they chose an aquatic herbicide to remove much of the initial hydrilla biomass and to halt the production of the tubers and vegetative buds the plant uses to spread.

“We know it will take years to eradicate hydrilla totally, but this was an important first step,” said Roxanna Johnston. “We plan to repeat the treatment this spring and to continue to look for nonherbicide options where specific site conditions may be favorable.”

Ultimately, though, one of the best tools may prove to be public awareness. Officials are training volunteer surveyors to patrol both the inlet and Cayuga Lake for new infestations.

They are conducting workshops, holding information forums and manning booths in public gathering spots. Washing stations have been established so boats, canoes and kayaks can be cleaned after each use, avoiding transport of small hydrilla fragments to new locations.

“Everybody can take the responsibility to do something,” Johnston notes. “It’s important to learn how to recognize hydrilla, know where it has been spotted in the past and avoid boating and other water sports in areas that are infested. It’s also important to talk to your elected officials. Control can be costly, but that pales in comparison to the investment required if hydrilla gets the upper hand.”