Mike Naylor, MD DNR
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Eurasian Watermilfoil
Myriophyllum spicatum
Origin: Eurasia and Africa
Background
Introduced accidentally from Eurasia in the 1940s,
Eurasian milfoil possibly escaped from an aquarium or was
brought in on a commercial or private boat.
Distribution and Ecological Threat
Eurasian watermilfoil occurs in at least 33 states east of
the Mississippi River and has recently been found in
Colorado. It is abundant in the Chesapeake Bay, the tidal
Potomac River and several Tennessee Valley reservoirs.
Typical habitat includes fresh to brackish water of ponds,
lakes, slow-moving streams, reservoirs, estuaries and
canals. Eurasian watermilfoil is tolerant of many water
pollutants, tends to invade disturbed areas where native
plants are less able to re-grow and does not typically
spread into undisturbed areas where native plants are well
established. It can form large, floating mats of
vegetation on the surface of lakes, rivers and other water
bodies, preventing light penetration for native aquatic
plants and impeding water traffic. The plant thrives in
areas that have been subjected to various kinds of natural
and manmade disturbance.
Mike Naylor, MD DNR
|
Mike Naylor, MD DNR
|
Mike Naylor, MD DNR
|
Description and Biology
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Plant: an herbaceous aquatic plant in the water-milfoil
family (Haloragaceae); stems grow to the water surface,
usually extending 3 to 10 feet but as much as 33 feet
in length and frequently forming dense mats; stems are
long, slender, branching, hairless and become leafless
toward the base; new plants may emerge from each node
(joint) on a stem and root upon contact with mud.
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Leaves: bright green leaves are finely divided and
occur in whorls of three or four along the stem, with
12 to 16 pairs of fine, thin leaflets about 1/2 inch
long. These leaflets give milfoil a feathery appearance
that is a distinguishing feature of the plant.
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Flowers, fruits and seeds: Eurasian watermilfoil
produces small, yellow, four-parted flowers on a spike
that projects 2 to 4 inches above the water surface.
Flower spikes often remain above water until
pollination is complete. The fruit is a hard, segmented
capsule containing four seeds.
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Spreads: by rhizomes, fragmented stems and axillary
buds that develop throughout the year. Although seeds
are usually viable, they are not an important means of
dispersal.
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Look-alikes: hydrilla (Hydrilla verticillata),
other species of Myriophyllum and Elodea.
Prevention and Control
Large harvesting equipment can be used to mechanically
remove milfoil in larger areas; a sturdy hand-rake can be
used for smaller areas. Other options include manipulation
of water level, use of water colorants or floating aquatic
plants to reduce light penetration, physical barriers and
chemical control. Potential impacts to existing native
aquatic plant species should be evaluated carefully before
implementing any of these techniques.
Native Alternatives
Some aquatic nurseries carry native and non-invasive
alternatives. However, due to the similarity in appearance
among aquatic plants to the untrained eye, they are easily
confused. Contact your state natural resource agency,
native plant society or other resource (see
reference section) for assistance in locating species
appropriate to your location and site conditions.
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