INVASIVE PLANTS OF OHIO
Fact Sheet 12 - Factsheet in .pdf format
Eurasian water-milfoil is a non-native rooted aquatic plant with long stems that branch near the water's surface to create a canopy of floating foliage. The leaves are in whorls of four with 14-20 pairs of feathery leaf divisions. A spike of pink flowers emerges above the water and then falls horizontally when in fruit. Eurasian water-milfoil closely resembles the native northern water-milfoil (M. exalbescens). A reliable distinguishing characteristic is the number of leaf divisions; northern water-milfoil has fewer (5-12) than the non-native species.
Eurasian water-milfoil can grow in a variety of aquatic habitats, but prefers fertile, fine-textured inorganic sediments. It is an opportunistic species that invades disturbed lake beds, recreational waterways and slow moving streams. Optimal growth occurs in alkaline systems with high concentrations of dissolved inorganic carbon.
Native to Europe, Asia and northern Africa this plant was introduced to the United States by the aquarium industry. It has been spread both purposefully by fishermen who introduced it to lakes for fish habitat and accidentally when caught in boat propellers and carried to a new body of water. In the last five decades it has spread throughout much of North America from Florida to Quebec in the east, and California to British Columbia in the west. Eurasian water-milfoil was first found in Ohio in 1950 and is now common throughout the state.
Dense canopies of Eurasian water-milfoil shade out native vegetation, alter the species composition of aquatic invertebrates and may impair the ability of some fish species to spawn. As an opportunistic species, this plant starts growing early in the spring and is capable of rapid dispersion through fragmentation of plant parts. Each fragment is able to grow roots and develop into a new plant. Due to the plant's ability to form dense growths, water recreation activities such as swimming, boating and fishing are inhibited.
Mechanical cutters and harvesters, as well as hand-pulling, are the most common methods of Eurasian water-milfoil control. To be effective, all fragments must be collected and removed from the site to eliminate new establishments. Manipulations of the water level, where feasible, may have an effect on the plant. Low water levels can desiccate populations and high levels will "drown" the plants by not giving them access to enough light.
Fluridone® is a selective aquatic herbicide for Eurasian water-milfoil and other aquatic weeds that may be useful.
A native weevil (Eurhychipsis lecontei) has been found to feed and reproduce on Eurasian water-milfoil. This insect may be an excellent control method in that it is selective to this species and does not appear to feed on native water-milfoils. Other biological control methods including a fungus (Mycoleptidiscus terrestris) are currently being researched.
ADDITIONAL INFORMATION SOURCES:
Boylen, C.W., L.W. Eichler and J.D. Madsen. 1999. Loss of native aquatic plant species in a community dominated by Eurasian water-milfoil. Hydrobiologia 415: 207-211.
Hoffman, R. and K. Kearns, eds. 1997. Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants. Bureau of Endangered Resources, Wisconsin Department of Natural Resources.
Sheldon, S.P. and R.P. Creed. 1995. Use of a native insect as a biological control for an introduced weed. Ecological Applications 5(4): 1127-1132.