Eurasian milfoil

Eurasian milfoil (Myriophyllum spicatum ) is a feathery-looking underwater plant that has become a major nuisance in waterways in the United States. Introduced into the country over 70 years ago as an ornamental tank plant by the aquarium industry, it has since spread to the East Coast from Vermont to Florida and grows as far west as Wisconsin and Texas. It is also found in California. It is particularly abundant in the Chesapeake Bay , the Potomac River, and in some Tennessee Valley reservoirs.

Eurasian milfoil is able to tolerate a wide range of salinity in water and grows well in inland fresh waters as well as in brackish coastal waters. The branched stems grow from 1–10 ft (0.3–3 m) in length and are upright when young, becoming horizontal as they get older. Although most of the plant is underwater, the tips of the stems often project out at the surface. Where the water is hard, the stems may get stiffened by calcification. The leaves are arranged in whorls of four around the branches with 12–16 pairs of leaflets per leaf. As with other milfoils, the red flowers of Eurasian milfoil are small and inconspicuous. As fragments of the plant break off, they disperse quickly through an area, with each fragment capable of putting out roots and developing into a new plant. Due to its extremely dense growth, Eurasian milfoil has become a nuisance that often impedes the passage of boats and vessels along navigable waterways. It can cause considerable damage to underwater equipment and lead to losses of time and money in the maintenance and operation of shipping lanes. It also interferes with recreational water uses such as fishing, swimming, and diving. In the prairie lakes of North Dakota, the woody seeds of this plant are eaten by some waterfowl such as ducks. However, this plant appears to have little wildlife value, although it may provide some cover to fishlife.

Aquatic weed control experts recommend that vessels that have passed through growths of Eurasian milfoil be examined and plant fragments removed. They also advocate the physical removal of plant growths from shorelines and other areas with a high potential for dispersal. Additionally, chemical agents are also often used to control the weed. Some of the commonly used herbicides include 2,4-D and Diquat. These are usually diluted with water and applied at the rate of one to two gallons per acre. The application of herbicides to control aquatic weed growth is regulated by environmental agencies due to the potential of harm to non-target organisms. Application times are restricted by season and duration of exposure and depend on the kind of herbicide used, its mode of action, and its impacts on the other biota in the aquatic system.

See also Aquatic chemistry; Commercial fishing

[Usha Vedagiri ]

RESOURCES

BOOKS

Gunner, H. B. Microbiological Control of Eurasian Watermilfoil. Washington, DC: U.S. Army Engineer Waterways Experiment Station, 1983.

Hotchkiss, N. Common Marsh Underwater and Floating-Leaved Plants of the United States and Canada. Mineola, NY: Dover Publications, 1972.

Schmidt, J. C. How to Identify and Control Water Weeds and Algae. Milwaukee, WI: Applied Biochemists, Inc., 1987.