Photographer: Leslie J. Mehrhoff, University of Connecticut Source: Bugwood.org Copyright: CC 3.0 US
As the name suggests, Trapa natans is a perennial aquatic plant. It has a submerged stem that can reach up to 15 feet long. The flowers are white with four petals, and bloom in June. After insect pollination, nuts are formed. The seeds of this plant are very sharp, with four ½ inch, barbed spines that can cause injury if stepped on or handled.
Like other invasive aquatic species, water chestnut can form dense mats that limit light and severely impact aquatic ecosystems. The impedance of light also causes oxygen to decrease, increasing the potential for fish die-off. It is also able to outcompete native vegetation and serves no nutritional value for waterfowl. Additionally, water chestnut infestations limit boating, fishing, swimming and other recreational activities.
The barbed seeds can remain viable for up to 12 years, making eradication difficult. In addition to seeds detaching, this plant is also able to reproduce by the rosette. The barbs on the seeds can attach to waterfowl, birds, other animals and objects, and allow them to spread farther.
How water chestnut was introduced to North America is unknown, but it was first observed in Massachusetts in 1859. It has since spread to several states in the Northeast.
Europe, Asian and Africa
U.S. Habitat: It prefers nutrient rich lakes and rivers, but it can grow in any freshwater area.
U.S. Present: CT, DC, DE, MA, MD, NH, NJ, NY, PA, RI, VA, VT and WV
For a county distribution map provided the EDDMapS click here.
Water chestnut is very persistent weed, making early detection the key to controlling it. This plant has been declared a noxious weed in Arizona, Massachusetts, North Carolina and South Carolina, and its sale is prohibited in most southern states.
Smaller populations are easier to handle because they can be pulled out individually. With larger populations, an integrated management strategy of mechanical and chemical treatment is suggested. Since new plants can be created from seeds and rosettes, complete plant removal is essential. However, the combined application of aquatic herbicides and mechanical harvesters can require over 10 years to be fully effective. Researchers are working on finding biological controls, but none have proven successful. Report any sightings to your local and state natural resource agencies!
Ding, J., Blossey, B., Du, Y., & Zheng, F. 2006. Impact of Galerucella birmanica (Coleoptera: Chrysomelidae) on growth and seed production of Trapa natans. Biological Control, 37(3), 338-345.
Fofonoff, P.W., G.M. Ruiz, B. Steves, A.H. Hines, and J.T. Carlton. 2003. Trapa natans. In: National Exotic Marine and Estuarine Species Information System: Chesapeake Bay Introduced Species Database.
Mills, E. L., Strayer, D. L., Scheuerell, M. D., & Carlton, J. T. 1996. Exotic species in the Hudson River basin: a history of invasions and introductions. Estuaries, 19(4), 814-823.
Orth, R. J., & Moore, K. A. 1984. Distribution and abundance of submerged aquatic vegetation in Chesapeake Bay: An historical perspective. Estuaries, 7(4), 531-540.