Bay Grasses > Water Chestnut

Significant declines in water chestnut harvested demonstrate the success of the removal effort. A mechanical harvester was necessary from 1999 to 2001 and infestations have been managed by DNR staff and volunteers in subsequent years.

The Sassafras population was believed to be slightly larger, but determining the exact quantity was not possible. Based on conversations with aquatic plant control experts from around the country, it was decided that application of the herbicide 2,4-D would be a safe and effective control technique. Despite this advice, public and state concern over the application of an herbicide to Chesapeake Bay waters lead DNR to save herbicide application as a last resort in the event that other techniques didn’t work. It was decided to launch a large mechanical and hand removal effort.

In 1999, hand harvesting was performed on June 11 and 12 on the Bird River, and June 13 and 14 in the Sassafras River. Between 50 and 80 volunteers spent each day in canoes harvesting plants by hand or with rakes. Mechanical harvesting using an aquatic plant harvesting boat took place on 14, 15 and 16 of June on the Sassafras, and 18 June 18 on the Bird, removing an estimated 260,000 pounds of water chestnut. Upon the discovery of additional plants in the areas previously harvested, a follow-up hand harvesting effort took place on July 7 and 8th, at which time the remaining plants were removed. All harvested plants were composted in the water using floating cages designed specifically for the project. This design was based on the floating composter used previously in Maryland.

In June 2000, follow up efforts were necessary to continue the attempted eradication. Once again, a combination approach was used, with mechanical harvesting by boat followed by hand removal by volunteers. On June 9 and 10, approximately 30 volunteers manually removed plants from the Sassafras River. On June 23 and 24 approximately 40 volunteers manually removed plants from the Bird River. Less than 1000 pounds of plants were discovered and removed from both rivers in 2000, indicating that mechanical and hand removal efforts were successfully reducing the total number of plants.

From June 15-20, 2001, a mechanical water chestnut harvester worked in both the Bird and Sassafras Rivers. In the Sassafras River, about 2 acres of Lloyds Creek and 3 acres of Shallcross Creek contained scattered plants. In these areas, the harvester cut and collected the majority of plants over the course of two days. Groups of volunteers then combed the river for additional plants on June 22nd and 23rd, removing several more bushels. In the Bird River, the harvester worked for one day, cutting less than 150 pounds of plants from a small tributary upriver of Railroad Creek. Volunteers finished the job on June 15th, with only a handful of additional plants being collected.

In 2002, efforts once again took place on both the Bird River (June 14) and the Sassafras River (June 28 and 29) for hand removal only with approximately 80 volunteers. Not enough plants were present at any of these locations to justify using a mechanical harvester- a significant milestone for the overall eradication effort, and one that we expect will continue. The total volume of plants harvested declined once again, with only a few bushels of plants harvested from the Bird River, and about 200 pounds of plants from the Sassafras. The combination of mechanical and hand removal of plants from 1999-2002 has proven to be so successful that there has been no need to resort to herbicides to control this pest. It is likely, however, that continued efforts at water chestnut harvesting will be needed for several more years before we are able to truly claim that the water chestnut infestation is a thing of the past.

From 2003 to 2007, control efforts were performed on both rivers using personal watercraft, DNR work boats, as well as canoes and kayaks. Beginning mid June, DNR personnel surveyed all shoreline areas in the vicinity of the original populations and for several miles along the shoreline both upriver and downriver. In each year, a few hundred plants were found in each river in generally the same areas as the first several years. In 2004, a substantial additional population of plants was discovered in a small pond off the eastern shore of Woodland Creek not easily visible from the river. Approximately 600 pounds of water chestnut were harvested from this pond and the cove into which it outflows. In 2005, no plants were found in this pond, but another pond was found across the river that also contained several hundred pounds of water chestnut.

In 2007, the Sassafras River Association joined the effort to control water chestnut, and assisted with the collection in June. Their volunteers met DNR staff on the river to harvest in Woodland and Turners Creek. Farther up the watershed, a private landowner off of Woodland Creek contacted DNR to request a biologist survey his sediment pond. Approximately 2 acres of the pond were covered with water chestnut, and after an unsuccessful hand removal effort, the pond level was lowered significantly over the winter. The reduced water level will expose roots and seeds in effort to desiccate the material on dry ground, and if further removal efforts are necessary, the pond will be easer to access.

An outreach effort was conducted though the Sassafras River Association to find any private landowners that may have water chestnut infestations on their property. DNR will follow up in 2008 to ensure no large populations exist that could flow in the river and its tributaries. The combination of mechanical and hand removal of plants from 1999-2007 has proven to be so successful that there has been no need to use herbicides. It is likely, however, that continued efforts at water chestnut harvesting will be needed indefinitely to keep the population in check and to prevent further spread. Funding is actively sought to allow an expansion of the control effort.