HISTORY Water chestnut (Trapa natans L.) is native to warm water

regions of Eurasia and, due to its edible fruits and reputed medicinal properties, the plants have long been widely distributed in Europe. It was first noted in North America sometime around 1874, where it was intentionally cultured in several Cambridge, Massachusetts ponds within the botanical garden of Asa Gray, famous Harvard botanist. By 1879, it was reported to be found growing in the Charles River. Wild populations have since become established in Vermont, New York, Virginia, New Hampshire, Maryland, Connecticut, Pennsylvania and southwestern Quebec.

IDENTITY Beneath its floating rosette of sharply toothed, rhombic-ovate

shaped leaves grows a long flexible stem with scattered feathery submersed leaves. Finely branched roots may weakly secure plants to bottom substrates. Once the initial shoot has developed its floating rosette, secondary offshoots with more leafy rosettes are rapidly formed. Some may detach and develop into separate plants. Inconspicuous, four petaled white flowers are produced in the center of the leafy rosette during July. Each flower contains a two chambered ovary and four stamens. After insect pollination, the fertilized flowers curve downward and then beneath the water they develop into large, sharp spined nut-like fruits about a month later. Plants continue to flower until killed by frost. The fruits fall to the lake bottom during autumn, overwinter, and then may germinate the following spring or remain dormant for as long as 12 years. In our climate, water chestnut is considered an annual but with its potentially long seed bank dormancy, it can persist for many years. Water chestnut was the poster child for Alive in New York: A Growing Invasion, a public education exhibit that continues to visit many New York State museums.

Water chestnut has many invasive attributes. It is a habitat generalist growing in shallow, nutrient-rich lakes and streams as well as stranded on wet mucky substrates. The extensive floating leaf rosettes effectively shade out native aquatic species. As the dense water chestnut plants die and decay, dissolved oxygen levels in the water may be lowered by microbial decomposers, leaving little dissolved oxygen for other organisms. Sharps spines on the fruit make it unpalatable, thereby lowering the carrying capacity of impacted sites for waterfowl. Each fruit can produce as many as 15 rosettes when it germinates. Each leaf rosette can produce as many as 20 fruits thereby demonstrating the high reproductive effort of this invasive plant. Dense growth of water chestnut can impede surface water navigation and the hard, sharp spines can easily penetrate water shoes creating a hazard for most water-based recreation.

A LOCAL EFFORT Water chestnut was known to grow in the Keuka Lake Outlet Marsh during the

1960’s but was thought to have been eradicated. It was rediscovered during the summer of 2009, and the Yates County Soil and Water Conservation District quickly assembled a response team. Participating organizations included the Finger Lakes Institute, Finger Lakes Community College and Keuka College as well as several volunteers from the Keuka Lake Association. Over the course of two days in September, large quantities of water chestnut were hand pulled from the marsh, loaded into college canoes and then transferred to a District pick-up truck. Upstream and downstream sites were searched but no additional infestations were discovered. Collected plants were composted far from the lake and any of its tributary streams. Plans are underway to repeat these management techniques during the summer of 2010. Because the infestation is small at the present time, the hand pulling technique is favored for its selectivity when compared to mechanical harvesting. To date, attempts to find suitable biological control agents have been unsuccessful.

What can you do to help? If you discover populations of water chestnut, contact:

1. Your local lake or watershed association 2. Your county Soil and Water Conservation District 3. Your local college or university

Watch for these additional invasive aquatic plants in your area:

Vouchered water chestnut

species distribution map from

New York Flora Atlas Project.

LOCAL EFFORTS TO ERADICATE WATER CHESTNUT (Trapa natans L.) Sarah Meyer1 and Bruce Gilman2

1 Finger Lakes Institute, Hobart and William Smith Colleges, 601 South Main Street, Geneva, New York 14456. smeyer@hws.edu, 315-781-4382.

2 Department of Environmental Conservation and Horticulture, Finger Lakes Community College, 3325 Marvin Sands Drive, Canandaigua, New York 14425-8395. gilmanba@flcc.edu, 585-394-3500 extension 7255.

Two truckloads of water chestnut

were removed after two days of

hand pulling in the Keuka Lake

Outlet Marsh.

yellow floatingheart brittleleaf naiad

European frog bit

curlyleaf pondweed

variable watermilfoil Eurasian watermilfoil

fanwort

Brazilian elodea

Special thanks go to… Yates County Soil and Water Conservation District

-Jim Balyszak, Colby Peterson, Richard Ayers, and Tom

Eskildsen

Finger Lakes Community College

-Dr. Bruce Gilman and students, Jake Keymel, Ben Galens,

Keith Sharpe, Mike Leworthy, Ethan Snyder

Finger Lakes Institute

-Marion Balyszak and Sarah Meyer

Keuka College

-Dr. Tim Sellers and students, Felicia Lenzo, Aimee Vilardo,

Mike Burley, Jon Bigelow, Danielle Doll, Darla Sucy

Keuka Lake Association

-Al Wahlig, Bill Laffin, Dave deCalesta

Yates Cornell Cooperative Extension

-Peter Landre

Flora von Deutschland Österrich und der Schweiz (1885)

Photo by Sarah Meyer

Photo by Sarah Meyer

Photo by Sarah Meyer

Photo by Kevin Colton Photo by Kevin Colton