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Elodea (Common Waterweed)

Elodea (Common Waterweed)

Elodea is one of the few pond plants that can remain green all winter long.

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Updated: February 25, 2008

Description

Dark-green leaves in dense whorls of two to three that become more crowded toward the top.
Grows in a variety of pond habitats but prefers to grow in fine sediments at the bottom of cool, spring-fed ponds.
One of the few pond plants that can remain green all winter long.
Reproduces primarily through stem fragments.

Value and Concern to the Pond

Provides excellent cover for aquatic insects and fish and serves as a source of food for various pond wildlife.
One of the few aquatic plants that provides underwater habitat during the winter months.
Modest amounts of elodea are generally considered beneficial for the pond ecosystem.
Dense growth of elodea can interfere with some uses of the pond, such as boating and fishing.
Excessive growth can also reduce dissolved oxygen levels during the summer causing fish kills.

Prevention

Overabundant growth of elodea is a symptom of excessive nutrients (phosphorus and nitrogen) in the pond water. These nutrients may come 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 Control

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

Biological Controls

Grass carp are an excellent alternative for elodea control since it is one of their preferred foods.
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 fact sheet titled Pond Owners Guide to the Use of Triploid Grass Carp in Pennsylvania available from your local Pennsylvania 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 elodea. You can learn more about these various herbicide options in Management of Aquatic Plants . Here are some tips for properly using an aquatic herbicide to control elodea:

Keep in mind that chemical control is often necessary every year or even multiple times during a year.
Make sure that you positively identify the plant as elodea 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.