Mike Naylor, MD DNR

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

• 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.
• 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.
• 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.
• 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.
• 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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Publication by USFWS BayScapes Conservation Landscaping Program
http://www.nps.gov/plants/alien/pubs/midatlantic/mysp.htm
Last updated: 7 October 2004