Invasive Species of the Pacific Northwest:
Eurasian Watermilfoil Myiophyllum spicatum
Jennifer Cunningham
December 5, 2014
FSH 423
Figure 1: Left picture shows the size and whorl arrangement. Right picture is M. spicatum growing in Liberty Lake,
WA. Photos from http://www.nwcb.wa.gov/detail.asp?weed=96 and http://libertylake.org/milfoil/
Classification
that will stay upright when out of the water
(WA. Dept. of Eco.).
Order: Saxifragales
Family: Haloragaceae
Genus: Myriophyllum
Eurasian watermilfoil can grow in fresh water as
deep as 20-30 feet. It is a rhizomatous plant that
forms dense mats that can become tangled
underwater.
Species: M. spicatum
Common Names: watermilfoil, spiked milfoil,
milfoil
Identification Key
Eurasian watermilfoil is a perennial,
submersed, aquatic plant. It has dissected leaves
that are feather like and arranged in whorls of
four. This plant is sometimes confused with the
native Northern watermilfoil (Myriophyllum
sibericum),
and
they
sometimes
are
distinguished using DNA for a positive
identification (WA State Dept. of Eco.).
Figure 3: Example of the whorl patter for Eurasian
watermilfoil. Photo from Washington State
Department of Ecology
Flowering stems can be seen extending above
the water’s surface. Tiny pink flowers with
either four or no petals grow in the axils of the
floral bracts which look like red spikes. The tips
of the stems are tassel-like and often red. The
stems branch out near the water’s surface and
can easily fragment.
Lower flowers are
pistillate, and upper flowers are staminate.
Figure 2: Eurasian watermilfoil on the left,
Northern watermilfoil on the right. Photo from
Washington State Department of Ecology
Eurasian watermilfoil has leaflets with closely
spaced segments of more than twelve pairs.
When pulled from the water, the leaflets tend to
collapse around the stem, unlike other milfoils
Figure 4: Examples of the stems of Eurasian watermilfoil
above the water’s surface. Photo from
www.nps.gov/plants/alient/pubs/midatlantic/mysp.htm
quickly enough to infest an entire lake within
two years (WA State Dept. of Ecology).
In spring, as the temperature reaches 60°F
(NOAA), its shoots will quickly grow and
breach the water’s surface above a dense
canopy. In mid to late July, the shoots will
flower (Dept. of Ecology of WA.).
Feeding Habits
Figure 5: An illustration of M. spicatum (Britton,
Eurasian Milfoil is a photosynthesizing
plant that relies on a supply of sunlight, water,
and carbon dioxide. Eurasian Milfoil requires a
lot of sunlight so it forms dense mats at the
surface of the water that can unfortunately shade
out plants below it, and it can reduce the amount
of oxygen in the water by preventing the wind
from mixing fresh oxygen into the water below
the canopy (WA State Dept. of Ecology).
1913)
Environmental Optima & Tolerances
Life History and Basic Ecology
Life Cycle & Reproduction
Eurasian watermilfoil is an aquatic plant
with rapid reproduction abilities. While it can
reproduce sexually, it rarely germinates the
hundreds of seeds it can produce. Instead, the
plant will fragment itself in autumn, and those
fragments can then be carried away by the wind,
waves, or human activities such as boating to
reproduce elsewhere (Dept. of Ecology State of
WA. and NOAA).
The annual growth pattern for Eurasian milfoil is
to fragment down to the crown in the fall, and
then the plant will overwinter with stored
carbohydrates. This plant does not produce
turions (Benson et al. 2004). There are some
cases in which the milfoil will overwinter in an
evergreen and maintain its biomass instead of
fragmenting to the crown. Milfoil can reproduce
M. spicatum prefers still or slow moving
water that is about 20 feet deep. It can be found
in clusters downstream, in small bodies of water,
or in coves because reproducing fragments are
carried there by wind and waves (King County
Gov., 2010).
A large reason for Milfoil’s success as an
invader is due to its adaptability. It can grow in
flowing water, in salinity up to 15 parts per
thousand (1/2 the salinity of the Sound), and in
depths up to 32 feet (WA State Dept. of
Ecology).
M. spicatum can tolerate a wide range of pH
(5.4-11), brackish water, and temperature ranges
(WA State Dept. of Ecology and King County
Gov., 2010). M. spicatum prefers inorganic
sediment, but it will grow on organic sediment
also (WA State Dept. of Eco.).
Since it reproduces from fragments, it grows
well in areas with disturbances like plant
management, motor
loading (NOAA).
boating,
and
nutrient
M. spicatum is a submerged aquatic plant, but if
its water source evaporates, it will develop a
land form (Jefferson County Gov.). That land
form can then return to its aquatic form when the
water level rises.
Biotic Associations (Pathogens, Parasites,
Commensalismes)
Dense growth of Eurasian milfoil
provides an ideal habitat for mosquito larvae
because there are few other invertebrates to
compete for space and few predatory fish to eat
the larvae (IN Dept. of Natural Resources).
Eurasian watermilfoil is known to cross with
native Northern watermilfoil, creating an
invasive hybrid (King County Gov., 2010).
Current geographic distribution
Currently, M. spricatum has spread to
44 of US States (Creed, 1998). In Washington
State, it can be found in several lakes such as
Lake Washington, Lake Sammamish, Lake
Union, Green Lake, and Liberty Lake (King
County Gov.2010). It can also be found from
Clallam and Jefferson counties on the western
most side of Washington to King County around
the Puget Sound up to Okanogan County by
Canada and down to Walla Walla County by
Oregon and the Columbia River (Nature
Mapping Foundation).
Figure 6: Distribution in PNW (USGS)
Figure 6: US distribution of M. spicatum http://enviroscienceinc.com/eurasian-watermilfoil-aquatic-weeds/
Figure 7: M. spicatum distribution in WA State 1996
http://naturemappingfoundation.org/natmap/water1/4mysppic.html
History of invasiveness
M. spricatum is native to Europe, Asia,
and North Africa (Eiswerth et. al. 2000).
It was most likely introduced through
Chesapeake Bay in the 1880’s, but its first
recorded collection was in Washington D.C. in
1942 (Eiswerth et al. 2000).
M. spricatum had spread to 33 states by 1985,
and it was first found in Washington State in
1965. The 1965 discovery in Lake Meridan,
King County, did not generate concern. It
wasn’t until 1974 when M. spicatum was found
flowing downriver from Canada’s Okanogan
Lake into Washington’s Lake Osoyoos that
management efforts were attempted (WA. Dept.
of Eco.).
Once M. spicatum was in Lake Osoyoos, it made
its way to the Columbia River.
It was
discovered in Western Washington in 1974 in
Lake Washington (WA State Dept. of Eco.).
By 1998, M. spicatum had spread to 44 states
and three Canadian provinces (Creed, 1998).
Invasion Process
Pathways, Vectors, and Routes
It is uncertain whether Eurasian
watermilfoil was first introduced through ballast
water or the aquarium trade, but several sources
site the aquarium trade as the most likely
pathway (University of Connecticut, 2009). It is
probable that the plant outgrew a tank which
was then dumped outside, and the plant’s
fragments made it to the watershed where it
established and spread (WA State Dept. of
Eco.).
Another pathway was shipping;
Earthworm farmers in Oklahoma used the plant
as packing material when they shipped out
boxes (WA State Dept. of Eco.)
The most common current pathway is
recreational boating (WA State Dept. of Eco.).
While there are warning signs and some boat
cleaning stations, often boaters transport small
fragments of the plant as they travel between
water sources.
While boats are the most common vector for M.
spicatum, anglers are also to blame for two
reasons. Some small fragments cling to their
equipment, and there are cases in which anglers
have been caught intentionally introducing the
plant into open water sources (WA State Dept.
of Eco.).
An obvious route in Washington State is along
the I-5 corridor (WA State Dept. of Eco.). This
is most likely due to boaters traveling along the
highway between water sources. Another route
is related to the history of migration of the plant
from Canada. M. spicatum can be found along
the Snake River, Okanogan River, and Columbia
River (Nature Mapping Foundation).
Factors Influencing Establishment & Spread
Eurasian milfoil is a plant that can live
for several weeks outside of water, making it
possible for it to survive clinging to aquatic
equipment that is transferred between bodies of
water (IN Dept. of Natural Resources). Since it
grows best from fragments and is tolerant of a
wide range of water temperatures and pHs, it can
quickly establish itself in a new area. Its high
adaptability lends to easy establishment and
spread.
spread out, they don’t swim in it either (WA
State Dept of Eco. and Aiken et al. 1979).
Since M. spicatum grows earlier and faster than
the native plants, it shades out the natives that
grow under its canopy (Smith and Barko 1990).
It is a leading cause in the displacement and
reduction of diversity of native aquatic plants
(Madsen et al. 1991 and USGS). There are less
macroinvertebrates present in the dense mats
(Keast, 1984) which has far reaching impacts on
the food cycle since the macros are a food
source for the native fish which are a food
source for the native waterfowl.
While M. spicatum reduces the amount of
macroinvertebrates in the water (see figure 15),
it does provide a perfect breeding habitat for
mosquito larvae (IN Dept. of Natural
Resources).
M. spicatum increases the phosphorous and
nitrogen in the water, increases the pH,
decreases the dissolved oxygen (DO), and
increases the temperature (WA state dept. of
eco.). It affects the DO in two ways. Since M.
spicatum has so much biomass, it affects the DO
as it decomposes because the bacteria needed to
break it down causes eutrophication in the water.
The other way it decreases DO in the water is by
preventing wind circulation with the water
below its thick canopy at the water’s surface
(EnviroScience, Inc.). Too little DO leads to
dead fish and a weak ecosystem.
Potential Ecological and Economical
Impacts
M. spricatum has several negative
impacts on the national, regional, and local
scales. At the water source, M. spicatum
provides a poor habitat for water fowl, fish, and
wildlife. The local waterfowl and fish do not eat
the plant, and since the plant is so dense and
Figure8: A dead fish in a tangle of M. Spicatum (WA
State Dept. of Eco.)
M. spicatum poses a significant economical
threat to Washington State. Every year, the state
spends around $1 million to control this weed
(Jefferson County Weed Control Board).
Uncontrolled, it clogs drains and dams causing
problems for power generation and irrigation
(WA State Dept. of Eco.).
On a recreational level, M. spicatum negatively
impacts swimming, fishing, and boating (IN
Dept. of Natural Resources). The plants are
commonly stuck in boat props and difficult to
detangle.
the amount of fish available in the water since it
negatively impacts biodiversity.
Management Strategies & Control
Methods
Risk minimization and early detection
are the best means of stopping the spread of M.
spicatum to new bodies of water. This means
thoroughly rinsing and cleaning all aquatic
equipment like boats, fishing rods, boots, and
trailers after exiting the water (Jeffereson
County Weed Council).
Some methods of control promoted by many
counties in Washington are covering the plant,
hand pulling, raking, lowering the water level,
rototilling, biological control, and herbicide
(Jefferson County Weed Council).
Covering the plant is useful with small quantities
of M. spricatum. It involves blocking the sun
with an opaque fabric to prevent photosynthesis
(Jefferson County Weed Council).
Figure9: M. spricatum caught in a boat prop
(EviroScience, Inc)
Swimming can be impossible and dangerous in
areas covered in M. spricatum. Between 1992
and 2003, there have been seven drowning
incidents where people became tangled in the
milfoil (Seattle Community Network). Several
triathlon competitors became tangled in milfoil
in the Columbia River in 2003 during a race
(Seattle Community Network). This has an
economic component because cities must close
parks and spend money to remove the plant for
public safety.
Recreational fishing is affected by the presence
of milfoil because it can be impossible to fish
through the canopy, and M. spricatum reduces
Figure10: 2008 Oswego graduate student pulling
Eurasian milfoil from Skaneateles Lake. (syracuse
news)
Hand pulling is similar to pulling weeds on land,
but the plants must be disposed of away from the
water source since the plant propagates from
fragments (Clallam County Weed Board). This
method is only useful in small bodies of water
but impractical in large bodies (King County
Gov., 2010).
Lowering the water level can be done in the
winter for several weeks which would expose
the M. spicatum to freezing temperatures. This
method must be carefully considered because it
would affect the whole ecosystem (IN Dept. of
Natural Resources). The other potential problem
is that M. spicatum can develop a land form for
survival which can transition back to an aquatic
form once the water table rises (WA State Dept.
of Eco.). For the water drawback to be most
effective, the crown of the plant should be
exposed to the coldest temperatures (IL Dept. of
Natural Resources).
The most effective
drawbacks occur when the environment allows
for the milfoil to dry out, and this can be
difficult in Western Washington since it often
rains through the year (WA State Dept. of Eco.).
spread further. Raking is ideal for maintaining
open water in areas around docks (King County
Gov., 2010).
Rototilling (rotovation) is a method that can help
the plant spread if not done correctly (Clallam
County Weed Board). The British Columbia
Ministry of Environment has a barge with a
mounted rototilling machine that can churn
down 8 inches into the sediment. The Eurasian
milfoil floats to the surface where it is collected
and disposed of (WA State Dept. of Eco.).
Harvesting is a method similar to rototilling, it
involves cutting the plant several feet below the
water’s surface and collecting the plant parts that
float to the top (WA State Dept. of Eco.).
Harvesting is only a temporary fix for the
problem since the plant grows back. Cutting,
harvesting, and tilling in King County requires a
permit since these mechanical procedures have
the potential to spread the plant further.
Figure 11: A Lake Placid Shore Owner raking Milfoil
http://www.adirondackdailyenterprise.com/page/content.d
Figure 12: Harvesting Eurasian milfoil in
etail/id/507278.html
Washington (WA State Dept. of Ecology)
Raking involves a rake attached to a rope that is
pulled through the water. This can help remove
plant density, but it does not pull up the root of
the plant. In many lakes, this method is not
allowed due to its negative impact on the
Sockeye Salmon Spawning areas (Jefferson
County Weed Council). This method creates
another potential problem in that it causes
fragmentation which can actually help the plant
Three types of biological controls have been
used for management: insects, Grass Carp, and
plant pathogens (WA State Dept. of Eco.).
The native milfoil weevil (Euhrychiopsis
lecontei) has had some success controlling
Eurasian milfoil, but it prefers the native
northern watermilfoil (Myriophyllum sibiricum).
There are three challenges for using the weevils
for control: large numbers of weevils are
difficult to obtain, it takes years for them to have
an impact, and they can only minimize rather
than eradicate the milfoil (King County Gov.
2010).
In the late 1960’s there was a mass dying of
Eurasian milfoil in Lake Venice in Maryland
which sparked interest in using plant pathogens
Figure 13: An adult milfoil weevil. Photo from EPA. http://water.epa.gov/type/lakes/images/bug.gif
The midge (Cricoptopus myriophylli) and
pyralid moth (Acetria ephemerella) are two
other biological insect controls (IL Dept. of
Natural Resources). The pyralid moth, while it
has a preference for Eurasian milfoil, is not
generally used as a control because it is a
generalist feeder with the potential for collateral
damage to the ecosystem (IL Dept. of Natural
Resources). This species also has low survival
rates.
In 1963, the Grass Carp (Ctenopharyngodon
idella) was introduced to control the M.
spricatum (IL Dept. of Natural Resources). In
multiple states, the carp has only eaten the M.
spicatum once the other sources of food have
been depleted, making carp a viable option only
in bodies of water with M. spicatum
monocultures (WA State Dept. of Eco.). Grass
Carp are not allowed in Lake Washington, Lake
Sammamish or any body of water where the
inlet or outlet can’t be screened to prevent the
escape of fish (King County Gov., 2010).
as a form of biological control (WA State Dept.
of Eco.). No pathogen was isolated, but a
fungus (Mycoleptodiscus terrestris) has shown a
strong ability to reduce M. spricatum in a
laboratory setup (NOAA).
2, 4-D, Diquat, diquat with copper, endothall
dipotassium salt, endothall with copper, and
fluridone are herbicides used in Washington to
control M. spricatum (WA State Dept. of Eco.).
Herbicides have shown positive results in
reducing milfoil presence.
Application is followed by diver surveillance
and hand pulling. Herbicides with copper can
only be used in irrigation ditches (WA State
Dept. of Eco.). Herbicides application requires a
permit and must be applied by a licensed
pesticide applicator (Clallam County Weed
Board, 2000).
Endothall and diquat are temporary controls
because they do not kill the roots (King County
Gov., 2010). Application of herbicides can be
beneficial when done to an area that has had the
water level lowered or when the water has
recently been dredged (King County Gov.,
2010). Herbicide is best applied in spring before
the plant is fully grown and in still water
(NOAA).
Figure 14: Aquatic plant sampling took place at irregular time intervals at Kohlman Lake. Dates without bars
indicates an absence of Eurasian water milfoil from the sampling locations. (Ramsey-Washington Metro Watershed
District 2012)
Expert Contact Information
Jenifer Parsons, WA State Dept. of Ecology's
botanist, [email protected]
King County Noxious Weed Control Program 206296-0290
Bellevue Manager [email protected]
Sammamish Manger [email protected]
Current Research & Management
Efforts
A researcher at the University of Washington is
conducting an evaluation of whether the milfoil
weevil will be a suitable control for Eurasian
watermilfoil in Washington. (WA State Dept. of
Eco.)
The US Army Corps of Engineers is continuing
research on plant pathogens for use on Eurasian
milfoil (WA State Dept. of Eco.).
Current management in Washington State is
multifaceted and depends on the area in need of
work. Multiple approaches discussed earlier are
considered and selected (King County Gov.,
2010). Of those methods, the most common is a
combination of herbicides and mechanical
removal (MN Dept. of Natural Resources).
An “Aquatic Plants and Fish” pamphlet is
published and distributed by the Washington
State Department of Fish and Wildlife to educate
the public (King County Gov., 2010). There are
also signs posted by infested water bodies to
inform the public about the plant and what to
do.
Bellevue closed the swimming areas at
Meydenbauer, Clyde, and Newcastle Beach Park
in July 2014 to apply herbicide to reduce the
Eurasian milfoil presence (Seattle Times News).
Figure 15: Rarefaction curves for invertebrate taxa on native and exotic milfoils in Saranac Lake (Wilson and Ricciardi, 2009)
Figure 16: Samples from various lakes in 2005 (Wilson and Ricciardi, 2009)
Literature Cited
Benson, A. J., C.C. Jacono, P.L. Fuller,
E. R. McKercher., and M. M. Richerson. 2004.
Summary Report of Nonindigenous Aquatic
Species in U.S. Fish and Wildlife Service
Region 5. U.S. Fish and Wildlife Service,
Arlington, Va. 145 pp.
Eiswerth, M.E., S.G. Donaldson, and
W.S. Johnson. 2000.Potential environmental
impacts and economic damages of Eurasian
watermilfoil (Myriophyllum spicatum) in
western Nevada and northeastern California.
Weed Technology 14(3):511-518.
Britton, N.L., and A. Brown. 1913. An
illustrated flora of the northern United States,
Canada and the British Possessions. 3
vols. Charles Scribner's Sons, New York. Vol. 2:
614. Courtesy of Kentucky Native Plant Society.
Scanned by Omnitek Inc.
Creed, R. P. 1998. A biogeographic
perspective on Eurasian watermilfoil declines:
additional evidence for the role of herbivorous
weevils in promoting declines. Journal of
Aquatic Plant Management 36: 16-22.
University of Connecticut. 2009.
Invasive Plant Atlas of New England. Eurasian
watermilfoil.
Madsen, J.D., J.W. Sutherland, J.A.
Bloomfield, L.W. Eichler, and C.W. Boylen.
1991. The decline of native vegetation under
dense Eurasian watermilfoil canopies. J. Aquatic
Plant Management 29:94-99.
Aiken, S.G., P.R. Newroth and I. Wile.
1979. The biology of Canadian weeds.
34. Myriophyllum spicatum L. Canadian Journal
of Plant Science 59:201-215.
Keast, A. 1984. The introduced aquatic
macrophyte Myriophyllum spicatum as habitat
for fish and their invertebrate prey. Canadian
Journal of Zoology 62: 1289-1303.
Smith CG, Barko JW. 1990. Ecology of
Eurasian watermilfoil). Journal of Aquatic Plant
Management 28:55-64
Wilson, Sara J. and Anthony Ricciardi.
2009. Epiphytic macroinvertebrate communities
on Eurasian watermilfoil (Myriophyllum
spicatum) and native milfoils Myriophyllum
sibericum and Myriophyllum alterniflorum in
eastern North America. Canadian Journal of
Fisheries and Aquatic Sciences 66: 21-24.
Key Sources of information
Department of Ecology for State of Washington
http://www.ecy.wa.gov/programs/wq/plants/wee
ds/aqua004.html
USDA
National
Agricultural
Library
http://www.invasivespeciesinfo.gov/aquatics/wa
termilfoil.shtml#cit
King County Noxious Weed Control Program
http://your.kingcounty.gov/dnrp/library/waterandland/weeds/BMPs/Milfoil_Myriophyllum_contr
ol.pdf
Liberty Lake Sewer & Water District 1
http://libertylake.org/milfoil/
Jefferson County Noxious Weed Control Board
http://www.co.jefferson.wa.us/WeedBoard/pdfs/
FactSheets/EurasianWatermilfoil.pdf
Clallam County Noxious Weed Council Board
http://www.clallam.net/weed/documents/eurasia
nwatermilfoil.pdf
Illinois Department of Natural Resources
https://dnr.state.il.us/Stewardship/cd/biocontrol/
6EurasianMilfoil.html
Indiana Department of Natural Resources
http://www.in.gov/dnr/files/EURASIAN_WAT
ERMILFOIL.pdf
Bugwood
Wiki
http://wiki.bugwood.org/Archive:BCIPEUS/Eur
asian_Watermilfoil#History_of_Biological_Con
trol_Efforts_in_the_Eastern_United_States
NOAA
http://nas.er.usgs.gov/queries/greatlakes/FactShe
et.aspx?SpeciesID=237
Seattle
Community
Network
http://www.scn.org/earth/savelake/You.htm
Nature
Mapping
Foundation
http://naturemappingfoundation.org/natmap/wat
er1/4spfrnox.html#eurmildist
EnviroScience,
http://enviroscienceinc.com/eurasianwatermilfoil-aquatic-weeds/
Inc
Minnesota Dept. Of Natural Resource
http://www.dnr.state.mn.us/invasives/aquaticpla
nts/milfoil/program.html
The
Adirondack
Almanack
http://www.adirondackalmanack.com/2012/06/
meet-the-invasive-milfoils.html
Ramsey-Washington
Metro
Watershed
http://www.rwmwd.org/index.asp?Type=B_BA
SIC&SEC=%7B845198F3-D798-42DF-92BD7F0683DFA82A%7D