THE ISSUE:  Water chestnut 

  Water chestnut (Trapa natans) is an annual aquatic plant that is native to Eurasia.  It was introduced into the U.S. as an ornamental, but then escaped.   It can form thick masses of vegetation in slow-moving bodies of water. Its presence can change aquatic habitat, remove available oxygen, and slow the flow of water. It can spread by seeds or by broken plant parts that are transported by water, animals, and watercrafts.    

Water chestnut is rooted with floating and submersed leaves. Stems are usually 6-8 feet long. Submersed leaves have a feathery appearance and form whorls around the stem.   Floating leaves are glossy, triangle shaped, have toothed edges, and form a rosette. A white 4 petaled flower is formed in the middle of each rosette. Nuts with sharp spines are produced, when ripe they can sink to the bottom and overwinter. Seeds can remain viable for up to 12 years.  

Integrated Pest Management (IPM) Options: 

• Prevention— Learn to identify this plant.  Never transport unknown plant material. Always clean recreational equipment before transporting! Never dispose of aquarium contents in bodies of water! 

• Mechanical— Because this plant reproduces from broken plant parts, mechanical removal alone may not be the best practice. Extreme care must be taken to remove all plant parts from the water. Mechanical removal in conjunction with other control methods can be effective. It is best to identify infestations early while they are small and can be removed carefully by hand.  

• Chemical—Herbicide applications in conjunction with other control measures may be necessary. Report any sightings of water chestnut to local authorities, who can help prescribe herbicide applications. Always read and follow herbicide label directions!

Justin Hatch, University of Idaho Extension Agriculture Educator in Caribou and Bear Lake Counties.
208-547-3205 [email protected]