INVASIVEalert

The distinctive leafy rosette of two-horned trapa. Photo credit: S. Tangren.

two-horned trapa

By Sara Tangren

A Close Relative

A different species (Trapa natans, fourhorned trapa) is invading waters from northern Maryland up through New England. It can be distinguished from two-horned trapa by the color of the flower (white instead of pale pink), color of the leaf underside (green instead of red/brown), and number of spines on the seed pod (four instead of two). The adverse consequences of infestation are similar for both species. Members of the public are encouraged to report any species of trapa they see. o

Two-horned trapa (Trapa bispinosa) was first found in North America in 1995, in the Northern Virginia counties of Stafford and Westmoreland. It has since been found in the nearby counties of Fairfax, Prince William, Fauquier, and most recently Loudoun. It establishes monocultures in areas of slow-flowing water up to 15 feet deep, The floating leaves block light, killing submerged aquatic vegetation (SAV) and reducing water oxygen levels. The thick vegetation makes boating difficult by impeding paddles and binding propellers. Recreational fishing is no fun because the lure becomes caught in the trapa weeds. To make matters worse, the seed pods have two long, sharp spines, which make working or playing in or near the infested water painful. These spines become caught in the feathers of resident geese, and this is probably how the plant is spread from one waterbody to another. As of the end of the 2021 growing season, only 76 ponds were known to be infested, all in Northern Virginia. The problem mostly affects private land owners with farm ponds and government agencies with stormwater detention ponds. This is a manageable number for a control program, but funding is needed to pay staff or contractors to do the work. Once two-horned trapa spreads into the open waters of the Potomac River and the Chesapeake Bay, it will damage aquatic habitat and impede recreational and commercial watercraft, causing considerable financial and recreational damage, and costing millions of dollars to control.

What to Do if You See It

Members of the National Capital Partnership for Regional Invasive Species Management (PRISM) are asking that citizens to keep an eye on local waterways for the presence of two-horned trapa. Webinars that teach citizen scientists how to recognize and report this plant will begin in May. Using firefighting as an analogy, these observations help define an area that is ablaze, or where Virginia property owners need removal support. They also help the scientists understand the rate at which the blaze is advancing each year.

Sara A. Tangren, Ph.D., is the coordinator of National Capital PRISM, Department of Energy & Environment, Government of the District of Columbia, Washington, DC. She can be reached at sara.tangren@dc.gov.

Resources

• To register for the Trapa Recognition & Reporting lunch webinar, September 13, 2022, go to: https://tinyurl.com/bdesn9ad • U.S. Geological Survey, NAS - Nonindigenous Aquatic Species: Trapa bispinosa. https://nas.er.usgs.gov/queries/ FactSheet.aspx?SpeciesID=2974