Water Chestnut
On this page:
- New York locations
- Identification
- How it spreads
- Environmental impact
- Management
- Best management practices for removal projects
Water chestnut is an aquatic invasive plant that is native to Eurasia and Africa. It was introduced in the United States in the mid-1800' as an ornamental plant. Around 1884, water chestnut was found growing in Collins Lake near Scotia, NY. Water chestnut colonizes shallow areas of freshwater lakes and ponds and slow-moving streams and rivers and negatively impacts aquatic ecosystems and water recreation.
New York Locations
Water chestnut has been found in more than 40 counties in New York State. For a map of where water chestnut has been documents, please visit iMapInvasives' interactive mapper (leaves DEC website).
Identification
Water chestnut is an annual plant with a submerged stem 12-15 feet long that has fine roots that anchor it to the soil. Its floating leaves are triangular in shape with saw-toothed edges and hollow air-filled stems. Leaves form a rosette around a central point. Its tiny flowers generally bloom in June and are four-petaled and white. Each rosette can produce up to 20 hard nut with four-inch spines that have barbs along them. Seeds within fruits can remain viable for up to 12 years.
How It Spreads
Water chestnut spreads by rosette and fruits detaching from the stem and floating to another area. They also spread by clinging to floating objects including recreational watercraft, the pads of boat trailers, and fishing equipment.
Environmental Impact
Water chestnuts form dense mats of rooted vegetation that can be very difficult to get through in a boat, kayak, canoe, or when swimming. Water chestnut fruits are often found along the shoreline and bottom of waterways - they have very sharp spines with barbs that can cause painful wounds when stepped on. The dense mats of vegetation shade out native aquatic plants that provide food and shelter to native fish, waterfowl, and insects. Decomposition of these dense mats reduces dissolved oxygen levels and may kill fish. Property values along shorelines of infested waters may also decrease.
How You Can Help
Prevention is the most effective method for dealing with invasive species. If they are never introduced, they never become established.
- Clean, drain, and dry your watercraft, trailer, and equipment before and after each use. Regulation 6 NYCRR Part 576 requires everyone who uses watercraft on public waters to, when possible, use the following methods to fully decontaminate your equipment:
- Clean the outside of the watercraft and trailer with high pressure (2500 psi) hot water (140°F) for 10 seconds.
- Flush the inside of the motor and all compartments (bilge, live well, bait buckets, ballast, etc.) with hot water (140°F) for two minutes.
- Soak fishing gear and equipment in hot water (140°F) for two minutes.
- Dump bait bucket water where it came from or on land.
- View more information on how to clean your boat.
Early detection of infestations helps to reduce removal costs and ecological impacts.
- If you think you've found water chestnut please take several photos and submit a report to iMapInvasives (leaves DEC website).
- Become a Chestnut Chaser! We know that water chestnut is underreported in New York State. Each summer we encourage folks to survey their favorite swimming holes, lakes, ponds, and nearby waterbodies for water chestnut and submit reports to iMapInvasives.
- Share the water chestnut fact sheet (PDF) with others.
Management
Water chestnut can be controlled using manual, mechanical, and chemical methods. As with all other infestations, early detection is key for containing and controlling spread. DEC is currently funding research on biocontrol - a study of the effectiveness of predator insects from water chestnut's native range - in controlling the spread of water chestnut.
The smaller the size of the infestation, the more easily it can be eradicated, and its economic and ecological impacts reduced. Because water chestnut is an annual plant, effective control can be achieved if seed formation is prevented.
A site may be a candidate for eradication (eliminating the plant from the area entirely) if:
- small in size (trace-sparse density),
- detected and treated early (no significant seed bank has been established),
- located within an isolated body of water, or is an isolated population within a larger body of water (unlikely to be re-infested),
- clean, drain, dry participation prevents new introductions,
- there is safe access for manual (hand-removal) efforts.
A site may be a candidate for suppression and containment (reducing the size of the patch or preventing it from spreading) if:
- medium in size (sparse-medium density),
- a long-term commitment to management/monitoring as seeds in the seed bank may be viable for up to 12 years,
- clean, drain, dry participating prevents new introductions,
- strategic removal of portions of the infestation would protect high quality native plant beds or other important features.
A site may be a candidate for maintaining access (preventing the patch from obstructing use) if:
- large in size (medium-dense density),
- population (and seed bank) has been established for many years,
- repeated introductions are likely from other nearby infestations due to tides/streamflow/motorboat transport, etc.,
- adjacent to boat ramps, docks, swimming beaches, or sampling sites where need for access makes continued maintenance necessary.
Best Management Practices for Removal Projects
Hand-pulling/Manual Removal
- Hand-pull rosettes when they first appear (mid-June to early July), before seeds are developed.
- Remove as much of each plant as possible, including the stems, any developing seeds, and roots.
- Avoid pulling native aquatic plant species, if possible.
- Identify access areas, disposal site, and location for storing harvested plants during the drying process.
- Start at the edge of the infestation and work towards the center.
- If possible, revisit the site repeatedly to pull plants that continue to sprout throughout the growing season.
- Repeat plant removal early each growing season until the seed bank has been depleted.
- Monitor site for a minimum of 12 years to ensure seed bank has been depleted and no new introductions have occurred from other sources.
Mechanical Removal/Machine Harvesting
- Conduct an aquatic plant survey to determine whether harvesting would also eliminate native and/or protected species.
- Identify access areas, disposal site, and location for storing harvested plants during the drying process.
- Harvesting machines can be used when rosettes first appear (mid-June to early July) before seeds are developed.
- Remove as much of each plant as possible, including the stems, any developing seeds, and roots.
- Repeat plant removal early each growing season until the seed bank has been depleted.
- Monitor site for a minimum of 12 years to ensure seed bank has been depleted and no new introductions have occurred from other sources.
- Avoid mechanical harvesting if water chestnut is accompanies by other invasive species that reproduce via fragmentation such as Eurasian watermifoil (leaves DEC website).
Chemical/Herbicide Control
- Aquatic herbicides approved for use in New York can be effective including florpyrauxifen-benzyl, imazamox, 2, 4-D, and glyphosate.
- Herbicides must be applied by a licensed applicator according to label requirements and any necessary permit requirements.
- Conduct an aquatic plant survey to determine whether products would also impact native and/or protected species.
- Identify boundaries for the treatment area and determine any risks to non-target species.
- Repeat herbicide treatment or combine with manual and/or mechanical control methods until seed bank has been depleted.
- Monitor site for a minimum of 12 years to ensure seed bank has been depleted and no new introductions have occurred from other sources.
Disposal
- For small infestations, plants can be places in black trash bags and left in the sun before placing in trash; or
- dispose of plants in compost, far away from water sources, or allow to dry in piles far from water and then incinerate.
- Larger infestations will require careful coordination with local municipalities to transport plants/seeds away from water sources and compost them on land without risk of spreading the plants.