Graves Lovell, AL DCNR

Eurasian Water-Milfoil

Myriophyllum spicatum L.
Water milfoil family (Halogoraceae)

Origin: Eurasia and Africa

Background
Introduced accidentally from Eurasia in the 1940s, Eurasian water-milfoil possibly escaped from an aquarium or was brought in on a commercial or private boat.

Distribution and Habitat
Eurasian water-milfoil 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. It is tolerant of many water pollutants.

Ecological Threat
Water-milfoil tends to invade disturbed areas 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, that impede water traffic and reduce light for native aquatic species. It thrives in areas that have been subjected to natural and man-made disturbance.

Description and Biology

• Plant: herbaceous aquatic plant; stems grow to the water surface, usually extending 3-10 ft. but as much as 33 ft. 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, finely divided and occurring in whorls of three or four along the stem, with 12-16 pairs of fine, thin leaflets about ½ in. long that give it a feathery appearance.
• Flowers, fruits and seeds: produces small, yellow, four-parted flowers on a spike that projects 2-4 in. above the water surface; flower spikes often remain above water until pollination is complete; fruit is a hard, segmented capsule containing four seeds.
• Spreads: vegetatively 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: many species of submerged aquatic plants including non-native invasive parrot-feather (Myriophyllum aquaticum), and native species such as Northern water-milfoil (M. sibiricum), coontail (Ceratophyllum dmersum) and water marigold (Megalodonta beckii).

Alison Fox, UFL

Mike Naylor, MD DNR

Prevention and Control
Large harvesting equipment can be used to mechanically remove Eurasian water-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 using any of these techniques.

Native Alternatives
Aquatic plant species are difficult to tell apart to the untrained eye. Contact your state natural resource agency, native plant society or other resource (see References) for assistance.