Myriophyllum spicatum L.

Eurasian Water-milfoil

Threat Level	Category
Established	Aquatic

Similar Species May be confused with the following native and/or non-native species. Landscape Alternatives lists native horticultural substitutes	Haloragaceae Family

Description

Height

The plant usually grows between 3.3-9.8 feet (1-4 m) but can extend up to 33 feet (10 m). The stems grow to the surface of the water and frequently form dense mats.

Stem

Stems are long, slender, branching, glabrous, and become leafless toward the base. Each floating node can become established if it comes in contact with mud.

Leaves

The grayish-green leaves are in whorls of three or four with 12-16 pairs of fine, thin leaflets up to 1.4 inches (35 mm) long. These leaflets give the leaves a feathery appearance that is a distinguishing feature.

Flowers

The yellow flowers are on a spike that is produced 2-4 inches (5-10 cm) above the water surface. The spike appears essentially naked and interrupted. Bracts are inconspicuous with the lower bracts usually toothed, sometimes entire, mostly exceeding the flowers. Stamen number is eight. Blooms July-September.

Seeds

Fruit is a dry capsule that splits into segments containing four seeds. Matures late July-September.

Images

Photo: Alison Fox, University of Florida, Bugwood.org
More images of Myriophyllum spicatum

Life History

Eurasian Water-milfoil is a perennial, aquatic, submersed herb that was accidentally introduced from Eurasia, probably in the 1940s. This plant can form large mats of floating vegetation on the water surface preventing light penetration thus outcompeting native plants and impeding water traffic. The preferred habitat for Eurasian water-milfoil is fresh or brackish water of fish ponds, lakes, slow-moving streams, reservoirs, and canals. Dispersal is primarily by fragmentation. It belongs to the primarily aquatic Haloragaceae family.

Seeds are usually viable, but are unimportant as a means of dispersal. Most regeneration is from rhizomes, fragmented stems, and axillary buds that develop throughout the year. Plant fragments can attach to objects in the water such as boats, trailers, or animals and be moved from one body of water to another. Motor boats can produce many fragments when traveling through the water. Flower spikes often stand above the water until after pollination and then re-submerge.

Habitat

Typical water-milfoil habitat includes fresh to brackish water of fish ponds, lakes, slow-moving streams, reservoirs, and canals. It is tolerant of many water pollutants. Eurasian water-milfoil does not spread rapidly into habitats where native plants are well established and tends to exist in habitats where native species grow poorly or cannot adapt. By altering waterways, we have created an unnatural, disturbed environment where water-milfoil thrives.

Origin and Distribution

Eurasian water-milfoil is a native of Eurasia and Africa. It occurs in almost all states east of the Mississippi River. It is abundant in the Chesapeake Bay, the tidal Potomac River, and several Tennessee Valley reservoirs. Two theories exist as to how it entered North America - it either escaped from an aquarium, or was released in shipping. This exotic aquatic plant species has been considered a problem in the United States since the 1940s. In the Tennessee Valley Authority reservoir system, a resort owner is thought to have introduced water-milfoil in 1953. Other states where invasive: WA, OR, ID, NV, CA, WI, MI, OH, PA, NY, VT, NH, CT, NJ, DE, VA. Federal or state listed as noxious weed, prohibited, invasive or banned: AL, CO, CT, FL, ID, ME, MA, MT, NV, NM, NC, OR, SC, SD, TX, VT, WA.


Sources: Information on this plant page derived primarily from the Tennessee Management Manual and Great Smoky Mountains National Parks Integrated Pest Management Plan.

Management Recommendations

Mechanical Controls

Harvesting: Large equipment exists to mechanically remove milfoil in larger areas. A sturdy hand-rake can be used for smaller areas, such as around docks, swimming areas and harbors. For the single harvest, harvesting should take place just before peak biomass is obtained. There may be substantial regrowth if done too early. Better results appear with multiple harvests in the same growing season. If multiple harvests are not possible, then sustaining annual harvests is an option. All fragments of milfoil plants must be removed to achieve adequate control.

Water Levels: Where water levels are under manual control, raising or lowering of the water can have an effect on the milfoil. By raising the water level, plants can be "drowned" by not having access to enough light. By lowering the water level, plants can be dehydrated and, at the right time of the year, frozen to death. This type of control is usually used in conjunction with herbicides and shade barriers.

Herbicidal Controls

Granular 2,4-D: This method is appropriate for large unmanageable areas of milfoil. This herbicide is soil active and is persistent for several months. 2,4-D is non-selective and will kill all plant species within the application zone; it should be used only as a last resort. Apply granules at a rate of 100 lbs per acre of water. The herbicide will sink to the root zone and kill the plant.

Other Controls

Heat: The viability of milfoil fragments is severely reduced after being subjected to temperatures between 45-50 ºC in the cooling systems of thermal electricity generating systems.

Light: The amount of light reaching the plant can be limited by changing water levels using backside plantings or floating plant species, light limiting dyes, or shade barriers.

Booms: Barriers are used to prevent the movement and spread of aquatic weeds. Usually the barrier is a blocking screen that hangs vertically from a cable to a depth of about 4 meters, and the cable is suspended by drum floats. This will not eradicate milfoil, but it can limit spread.