Eurasian Watermilfoil in Vermont
A problem in Vermont
Eurasian watermilfoil (Myriophyllum spicatum L.) is a non-native aquatic plant that currently infests a
number of Vermont lakes (pdf, 117 KB), including the state's largest, Lakes Champlain, Memphremagog and
map). This plant is known for its rapid growth and ability to spread, which can lead to significant
problems within a lake. Commonly found in
shallow bays and along the shoreline, milfoil forms dense beds that can seriously impair the recreational use of a
lake, reduce the availability of fish spawning grounds, outcompete beneficial native plants, and otherwise alter a
lake's natural environment.
The growth and spread of Eurasian watermilfoil is a threat to all our lakes and ponds. Once Eurasian watermilfoil has infested a lake there is no known way to eradicate it. Lake managers can only seek to control it by integrating the
most effective, economically feasible, and environmentally sound methods available.
Eurasian watermilfoil is not native to North America but originates from Europe, Asia and northern Africa. As an
"introduced" species to this continent, Eurasian watermilfoil has no natural controls (insects, bacteria, fungi) to keep its
growth in check. In North America it has the potential to completely
infest lakes once introduced. Native types of
watermilfoils rarely attain such extensive growth.
Eurasian watermilfoil stems can reach the surface in up to 20 feet of water, growing up from the lake bottom each
year from a fibrous root system. Milfoil grows and spreads extremely quickly, forming dense surface mats. Unlike most
native aquatic plants, which are usually associated with particular water qualities, Eurasian watermilfoil will grow
readily in many types of lakes, as well as on almost any lake bottom type: silty, sandy, or rocky.
The presence of Eurasian watermilfoil often brings a change in the natural lake environment. Over time, it may
out-compete or eliminate the more beneficial native aquatic plants, severely reducing natural plant diversity within a
lake. Since its growth is typically dense, milfoil weed beds are poor spawning areas for fish and may lead to
populations of stunted fish. Although many aquatic plants serve as valuable food sources for wildlife, waterfowl, fish,
and insects, Eurasian watermilfoil is rarely used for food. Commonly found in shallow bays and in bands along the shoreline, dense surface mats of milfoil can also make fishing, boating and swimming virtually impossible.
Eurasian watermilfoil reproduces almost exclusively by the breaking off of fragments which can drift away, sink, develop roots, and grow into new plants. A fragment just a few inches long is capable of starting a new plant. This fragmentation occurs both naturally and as a result of human activity. Within a lake, wind and waves may break plants loose, allowing them to drift into new locations and root. Boating activity through dense milfoil beds also contributes to the fragmenting and spread of milfoil plants.
Eurasian watermilfoil is recognized primarily by its whorls of four feather-like leaves around the stems. Each leaf is finely divided into paired leaflets,
typically 12 to 21 pairs per leaf. The number of stems per plant increases as the plant ages. Each individual stem branches several times as it nears the
water surface, creating a dense floating mat over the surface of the lake. *The tops of the milfoil plants, both stems and leaves, often turn red in color.
Erect flower spikes rise above the water surface, and flowers are small and reddish in color. Dense Eurasian watermilfoil beds usually occur in water between
3 and 20 feet deep. Click here for a detailed image of Eurasian watermilfoil.
Since many aquatic plants found in Vermont's lakes look quite similar, distinguishing one type of plant from another
can be difficult. Native aquatic plants which are easily mistaken for Eurasian watermilfoil and can be found in
Vermont lakes are shown below. These illustrations depict each plant's leaf arrangement on the stem and are
intended to help in distinguishing one species from another.
Leaves are arranged in whorls of 4 around the stem. Each leaf generally has fewer than 12 pairs of leaflets.
Leaves are arranged in a whorl around the stem. Each leaf is toothed and branches only once or twice.
Leaves are opposite on the stem, appearing whorled. Each leaf is toothed and tapers to a sharp point.
Leaves are arranged alternately on the stem. Each leaf branches many times and often bears small sacs or bladders.
How is Milfoil Spread?
Human recreational activities usually account for the spread of non-native aquatic plants and animals between lakes.
Fragments of aquatic plants cling to the propellers of boat motors or to boat trailers and, if not removed, can start new
populations when the boat is launched into another waterbody. Unfortunately, once Eurasian watermilfoil has been
introduced into a lake, there is no way to completely eradicate it.
To stop the further spread of non-native aquatic species, it is imperative that all plant fragments are removed from
boats before putting in or leaving a lake's access area. Removed plant material should be properly disposed of in a
trash receptacle or on high, dry ground where there is no danger of them washing into any waterbody.
It illegal to transport Eurasian watermilfoil, water chestnut, zebra mussels or quagga mussels to or from any Vermont surface water. Any person found
transporting these species to or from a Vermont lake or pond will be in violation of this law. Violators are subject to a penalty of $150 per violation
(pursuant to 10 V.S.A.§1266).
A state noxious weeds quarantine rule (pdf, 106 KB) also prohibits the transport of many aquatic weeds, as well as their sale, distribution, possession, or cultivation.
Since there is no way to completely eradicate Eurasian watermilfoil from a lake once it has been introduced, control
efforts must instead focus on: controlling newly introduced infestations, preventing further spread of the plant, or
reducing the nuisance level of the problem. Some methods are more appropriate for well-established populations, while
others are better suited for those that are recent introductions.
The State of Vermont is concerned about the impacts certain milfoil control methods could have on the environment.
Bottom barriers, all mechanically powered devices (harvesters, hydrorakes), herbicides, and biological controls
require permits from the Department of Environmental Conservation before they can be used to control nuisance aquatic plant growth. Contact the Department at (802) 241-3777 to determine if your proposed control method requires a permit and to obtain permit applications.
Bottom Barriers, specially made sheets of materials such as fiberglass, polypropylene, or polyvinyl chloride (PVC), anchored to a lake bottom will prevent plant growth by blocking sunlight. Bottom barriers are most appropriate to control growth in localized areas such as in swimming areas, around docks or to create boat lanes out to deeper water.
With diver operated suction harvesting, scuba divers use suction hoses powered by a surface compressor to selectively remove milfoil from the lake bottom. Although too labor intensive on a large scale, this method has proven to be highly successful at combating newly established infestations in Vermont lakes.
A hydrorake removes plant roots and shoots by raking the lake bottom. Any removed material must then be deposited on shore. Hydroraking has had limited use in the state but is most practical for providing short-term relief from dense milfoil infestations.
When done properly, pulling milfoil plants by hand is highly effective for controlling small, newly introduced milfoil populations.
Mechanical harvesters cut off the milfoil (and any other plants) below the water surface, gathering the cut material as they move through the plant bed. Milfoil roots are not removed in this process. Mechanical harvesting, like lawn mowing, merely reduces the height of plant growth temporarily in order to make the lake more usable. Removing the plant material from the lake does however, prevent the plants from contributing to the sediment which rapidly
accumulates under dense aquatic plant beds. Mechanical weed harvesting has been used on several heavily infested Vermont milfoil lakes.
Other potential milfoil control methods include rotavating, chemical herbicides and biological controls such as grass
Rotavating involves a machine that "tills" the lake bottom, dislodging both the roots and stems of the plant. Plants are either collected by a mechanical harvester or, if conducted in the late fall, are allowed to wash ashore and dry over the winter. This method has yet to be used in Vermont.
There are a number of federally registered aquatic herbicides that control Eurasian watermilfoil. Considerations for use include cost, the potential need for repeated applications, and product label restrictions that prevent their application in lakes used as water supplies
Biological controls such as insects, bacteria or fungi that will impact milfoil are in the experimental stages only. Their use as a milfoil control method may prove to be the control of the future. The use of plant-eating fish such as the grass carp, a native to China, is currently illegal in Vermont.
The VTDEC has been working with the watermilfoil weevil Euhrychiopsis lecontei since 1989. The weevil was responsible for at least one Eurasian watermilfoil decline in Vermont, in Brownington Pond in Brownington. It has been found naturally occurring in many other milfoil-infested lakes in Vermont. The weevil, a native aquatic insect, has shown promise as a potential biological control agent for Eurasian watermilfoil, and is currently the subject of ongoing research.
- Additional Weevil Information:
Updated: January 2004