The U.S. Army Corps of Engineers’ (USACE) Engineer Research and Development Center (ERDC), in cooperation with the Virginia Department of Wildlife Resources (DWR), will conduct a demonstration project at Lake Brittle, Virginia, to evaluate the effectiveness of three U.S. Environmental Protection Agency-approved aquatic herbicides, flumioxazin, imazamox, and florpyrauxifen-benzyl, in controlling the invasive two-horned water chestnut. 

Treatment will be conducted early summer 2025 prior to the two-horned water chestnut going to seed (pre-emergent).

Lake Brittle was selected as the preferred alternative site in collaboration with Virginia DWR to deploy an early detection-rapid response multi-agency approach with the goal of eradicating T. bispinosa var. iinumai in Virginia.

The results will help determine the most effective herbicide, best treatment timing, potential effects on non-target species, and proper herbicide exposure times. Findings will inform future management practices and will be shared with state, regional, and local agencies, as well as nonprofits, to support broader efforts to control two-horned water chestnut in Virginia and Maryland.

USACE has prepared a draft Environmental Assessment and Finding of No Significant Impact under the National Environmental Policy Act to document the effects of the herbicide applications at Lake Brittle.

The ERDC demonstration project will only be conducted for one season. ERDC staff will then monitor the site to understand herbicide impacts and population changes.

Two-horned water chestnut (Trapa bispinosa) is an annual aquatic plant found in freshwater habitats, typically in still or slow-moving water. Native to East Asia (Taiwan, Japan, China, and Korea), it was first reported in the U.S. in 2014 in Pohick Bay on the tidal Potomac River near Lorton, Virginia. Initially mistaken for Eurasian water chestnut, it was later confirmed to be a genetically distinct species.

In late May, its triangular, serrated leaves begin to emerge on the water’s surface, forming rosettes. These floating leaves are green on top and reddish underneath. The plant’s roots can anchor in sediment up to 15 feet deep, and its stems contain air pockets that help it float. By June, light pink flowers bloom in the center of each rosette and develop into two-horned seed pods. The plant dies back after the first frosts in November, but its seeds can remain viable in sediment for at least two years.

The plant’s hard, spiny seed pods are notorious for clinging to waterfowl, boats, nets, clothing, and construction equipment. It has been documented in Virginia’s Fairfax, Fauquier, Prince William, and Loudoun counties, and Maryland’s Prince George’s County.

This invasive species is not only disrupting ecosystems but also threatening our ability to safely enjoy our local waterways. Awareness and early intervention are key to stopping its spread.

Two-horned water chestnut forms dense mats on the water’s surface, limiting sunlight, suppressing the growth of native aquatic plants, and reducing oxygen exchange. These effects contribute to declining water quality and threaten aquatic life. It spreads rapidly and can dominate habitats, impacting recreational use of waterways like boating, fishing, and swimming.

Impact to locals and the recreating public at Lake Brittle during this work is expected to be minimal and temporary. Treatment areas are small and will be reopened within approximately two hours, once the foliar application is complete and the chemicals have dried. In the long term, the work will have positive effects by reducing the spread of two-horned water chestnut, improving access for recreational activities, and enhancing the lake’s overall aesthetic value.