Since 2000, the aquatic invasive species known as Trapa bispinosa (two-horned water chestnut or two horned trapa) has spread to more than 60 known locations in Fairfax County. The county is raising awareness and asking for help detecting, reporting, and eradicating the invasive plant.
The plant is found in rivers, tidal bays, and ponds throughout Fairfax County and is distinguishable by its triangular-toothed leaves. Typically, infested waterways suffer from degraded water quality and detrimental impacts to surrounding habitats. Spring is the peak season in which seedlings sprout and it rapidly spreads within a water body. The plant typically emerges from seeds between April and May and once summer comes, infestations spread across the water body rapidly and become more difficult to eradicate. It will flower, fruit and the leaves become dense and visible on the water surface from June to September. All the leaves die back with a hard frost in December, leaving just the viable seed in the bottom sediment. The previous year’s black, two-spined seed hulls (1 inch wide) can be found adrift along the shoreline any time of year.
Coordination among interested parties requires communication and we hope this site provides a platform where you can report a possible sighting (USGS - Sighting Reporting Form), ask questions and seek advice (Northern Virginia Soil and Water Conservation District), request control help from local environmental groups, and share experiences among social media groups. If you think you have trapa in your pond, we strongly urge you to follow these steps:
Allowing T. bispinosa to proliferate in your pond will create an abundant seed bank, which can in turn lead to this plant spreading to other water bodies. These seeds may transport by streams, creeks and flooding events that connect water bodies; but the most common vector is seed transport by waterfowl. The ‘horns’ of the seed pod become lodged for travel on a bird, leading to an unpredictable spread of this plant. If you have T. bispinosa in your pond, the problem may not be as isolated as you’d reasonably expect. If you have waterfowl visit your water body, you may one day have T. bispinosa.