New invasive aquatic plant confirmed in Vermont

Variable-leaved watermilfoil (Myriophyllum hererophyllum) (VTDEC)

In October 2008, aquatic biologists at the Agency of Natural Resources confirmed the arrival of a new invasive aquatic plant in Vermont, Myriophyllum heterophyllum (variable-leaved watermilfoil).  The plant was found  in Halls Lake (pdf, 230 KB) in Newbury located on the eastern side of the state.  Variable-leaved watermilfoil is a freshwater rooted perennial plant not native to Vermont.

What is the status of variable-leafed watermilfoil in Vermont?

How is variable-leaved watermilfoil identified?

Why is variable-leaved watermilfoil a problem?

How is variable-leaved watermilfoil spread?

How can I help?

Where can I find more information?

What is the status of variable-leafed watermilfoil in Vermont?

Staff at the Department of Environmental Conservation’s Lakes and Ponds Management and Prevention Section deployed rapid response initiatives shortly after receiving genetic confirmation of the plant’s identity.  An underwater search of areas of the lake where variable-watermilfoil might grow was conducted.  The survey results confirmed that variable-leaved watermilfoil appeared limited to one area of the lake.  Using a curtain to contain any floating stem fragments, a crew removed plants by hand over a three day period.  All removed plants were composted.

Variable-leaved watermilfoil appears contained in Halls Lake for now.  Future surveillance and spread prevention measures are critical to prevent further spread of this aggressive plant in Halls Lake and to other waters in Vermont.

How to identify variable-leaved watermilfoil

Variable-leaved watermilfoil (right) side by side with Eurasian watermilfoil (left). (VTDEC) Click image to see larger image (pdf, 940 KB)

Many watermilfoils, native or not, can be difficult to distinguish from one another, especially in the absence of fruits or flowers.  In addition to the non-native watermilfoils, variable-leaved and Eurasian (Myriophyllum spicatum), six native watermilfoils are known from the state.  To identify variable-leaved watermilfoil, look for:

• Densely packed whorls of four to six underwater leaves around the stem
• Underwater leaves with 7 to 11 pairs of leaf segments per leaf
• On more mature plants, blade-like leaves with serrated edges appearing above the water’s surface.  Flowers develop at the base of these above-water leaves, forming an erect, stiff spike. 
• Thick, robust, often reddish stems.

Note:  All leafy watermilfoil plants should be suspect until a positive identification can be made.  If you find a suspicious aquatic plant, contact Ann Bove, Vermont Aquatic Invasive Species Program immediately.

Dense variable-leaved watermilfoil in a New York Lake (VTDEC)

Why is variable-leaved watermilfoil a problem?

Variable-leaved watermilfoil can be difficult to control once a population is established in a waterbody.  Like Eurasian watermilfoil which was confirmed in Vermont in 1962, variable-leaved watermilfoil is able to grow in a wide variety of environmental conditions, is aggressive and grows rapidly.  Dense growth of variable-leaved watermilfoil crowds out beneficial native aquatic plants and can impair recreational uses including boating, fishing and swimming.

How is variable-leaved watermilfoil spread?

Spread of this species occurs by stem pieces, roots and seeds.  Plant parts can easily hitchhike on recreational equipment if not removed.  Variable-leaved watermilfoil is also a popular aquarium trade species, which could be a possible vector for invasive aquatic plant spread. Under Vermont’s Quarantine Rule, variable-leaved watermilfoil is a prohibited species.  Department staff, in cooperation with the Agency of Agriculture, Food and Markets, inspects Vermont aquarium retailers annually.  In 2008, officials found two retailers in southern Vermont selling variable-leaved watermilfoil.

How can I help?

• Don’t allow aquatic invasive plants or animals to hitchhike on your recreational equipment.   Before moving between waterbodies:

• Inspect boat, trailer, motor and other equipment for attached plant or animal material.
• Remove all plant and animal material.
• Discard removed material in a trash receptacle or on high, dry ground where there is no danger of them washing into any water body.
• Drain all water from boat, boat engine, and other equipment.
• Rinse all boat and trailer parts with tap water (preferably hot, high pressure).
• Dry boat, trailer and equipment out of water and in sun for at least five days.
  
• Become a VIP - Vermont Invasive Patroller - and monitor local waterbodies for new introductions of invasive species.   Attend a training session and learn how to identify and search for invasive aquatic plant and animals as well as learning about native aquatic plants and animals and their habitats.
• Dispose of unwanted aquarium plants and animals in the trash.  Don’t release any aquarium plants or animals into the wild.

More information

• Click here (pdf, 55 KB) for a copy of the Vermont Agency of Natural Resources October 16, 2008 press release on variable-leaved watermilfoil in Halls Lake.
• Click here (pdf, 230 KB) for a variable-leaved watermilfoil fact sheet.
• Click here (pdf, 230 KB) for a map of Vermont documented aquatic invasive species infestations, including the Halls Lake variable-leaved watermilfoil infestation.
• Visit the following websites for more information:
  • Maine Center for Invasive Aquatic Plants http://www.mciap.org/herbarium/invasive.php
  • Maine Department of Environmental Protection Invasive Aquatic Plants http://www.maine.gov/dep/blwq/topic/invasives/index.htm
  • New Hampshire Department of Environmental Services Exotic Species Program http://des.nh.gov/organization/divisions/water/wmb/exoticspecies/index.htm
    
• Contact Ann Bove, Vermont Aquatic Invasive Species Program.

Updated: November 2008