Eurasian Water Milfoil

Eurasian Milfoil is an invasive, nonnative, plant with long stems, often reaching to the surface, with feather like leaves in whorls of 4 or 5 around the stem.
Eurasian Water Milfoil - Articles
Eurasian Water Milfoil

Description

  • An invasive, nonnative, nuisance plant.
  • Long stems, often reaching to the surface of the pond, with featherlike leaves in whorls of four or five around the stem.
  • Stems reaching surface often branch to form a thick canopy on the water surface.
  • Distinguished from native, northern water milfoil by the number of leaf divisions (>14 in Eurasian water milfoil and <14 in northern water milfoil).
  • Native, northern water milfoil usually does not grow to nuisance levels.
  • Can grow in a variety of settings but prefers fine, organic sediments on pond bottom.
  • Reproduces primarily through stem fragments.

Value and Concern to the Pond

  • Eurasian water milfoil provides some underwater habitat for fish and invertebrates and serves as a source of food for some wildlife, but its rapid growth to nuisance levels limits these values.
  • Dense growth of milfoil at the pond surface can interfere with many pond uses.
  • Excessive growth can also reduce dissolved oxygen levels during the summer, causing fish kills.
  • Eurasian water milfoil should be eradicated as soon as it is observed in the pond.

Prevention

  • Overabundant growth of Eurasian water milfoil is a symptom of excessive nutrients (phosphorus and nitrogen) in the pond water from barnyards, crop fields, septic systems, lawns, and golf courses.
  • Control of overabundant aquatic plants is best accomplished by reducing or redirecting nutrient sources from the pond. This can be accomplished by reducing fertilizer applications near the pond, maintaining septic systems properly, redirecting nutrient rich runoff away from the pond, and maintaining vegetative buffer strips around your pond.
  • If you fail to address the underlying nutrient causes of aquatic plant growth, you will probably encounter a perpetual need to control overabundant plant growth.

Physical Controls

  • Harvesting by cutting or raking is not recommended because milfoil can reproduce rapidly from fragments.
  • Drawdown may be used during the winter to freeze the rootstock.

Biological Controls

  • Grass carp are an alternative for milfoil, although they rarely can eat enough to keep it under control.
  • Grass carp must be purchased from an approved hatchery after receiving a state permit.For more information on the grass carp permit and approved hatcheries, consult the grass carp fact sheet available from your local Pa. Fish and Boat Commission office or online at the Penn State Extension website.

Chemical Controls

There are numerous aquatic herbicides that can be used to control Eurasion water milfoil. You can learn more about these herbicide options in Management of Aquatic Plants . Here are some tips for properly using an aquatic herbicide to control Eurasian water milfoil:

  • Keep in mind that chemical control is often necessary every year or even multiple times during a year.
  • Positively identify the plant in your pond as Eurasian water milfoil before proceeding with chemical control.
  • Carefully measure the pond area and/or volume to determine the amount of herbicide needed. Consult the fact sheet titled Pond Facts 4: Measuring Pond Area and Volume  for more information.
  • Make sure that you obtain and submit the required state permit before applying the herbicide. Before applying a herbicide to your pond, you must obtain a state permit from the Pennsylvania Department of Environmental Protection. The two-page application form and instructions for this permit are online at Application for Use of an Algaecide, Herbicide, or Fish Control Chemical in Waters of the Commonwealth.
  • Aquatic herbicides can be purchased from some home and farm supply stores, hardware stores, or various online suppliers. Costs can range from less than $100 to more than $1,000 to treat a one-acre pond.
  • Follow the herbicide label carefully for specific instructions on when and how to apply the chemical.
  • Herbicide treatments should be done early in the growing season before the plants cover a large portion of the pond. Treatment of severe infestations may cause a fish kill due to reduced dissolved oxygen.

Additional Resources

For further information and publications on pond management visit the Penn State Extension website or contact your local extension office.

Prepared by Bryan R. Swistock, senior extension associate and Heather Smiles, fisheries biologist, Pennsylvania Fish and Boat Commission.

Authors

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