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Aquatic Weed Identification and Control

Aquatic Plants

Methods of Aquatic Weed Control

Aquatic plants fulfill many natural functions and definitely have important and vital roles to play in aquatic and swamp environments. However, they may interfere with man's use of the aquatic environment. Since many aquatic plants are desirable and in some cases necessary, you should control them only when they become a pest by interfering with use of a particular aquatic environment.

There are three methods to control aquatic weeds:
Mechanical control and environmental manipulation -- Mechanical methods may be as simple as cutting a willow tree or pulling or digging up a few objectionable plants that have just gotten started along the water margin. Mechanical methods also include using expensive and complicated underwater mowers. While cutting or removing a few plants by hand can be effective in small and limited areas, generally, mechanical aquatic weed control on a large scale is useless.

Environmental manipulation can be effective in certain situations. Small ponds that have extensive feather-edges can be reworked to deepen the edges to a minimum depth of 18 inches. This eliminates the habitat for many of the troublesome aquatic weeds. Deepening pond edges coupled with a good fertilization program will, in many cases, be the most economical and best method for controlling many aquatic weeds. See Extension Information Sheet 229 for proper pond fertilization methods.

Periodic winter drawdowns can also be effective and economical in controlling many aquatic weeds. This is only practical in ponds or lakes equipped with water-control structures. The time, amount, and length of drawdown depend on many factors to be successful. Usually the drawdown should be completed by November 1 and continued until there has been at least 3 consecutive days when the air temperature has been below 32 °F. For more information, request Extension Information Sheet 1501.

Biological Control -- This may be the most promising form of aquatic weed control. The long-term cost:benefit ratio can be extremely attractive.

The grass carp is an excellent biological control for some aquatic weeds in certain situations. The grass carp can be legally stocked in Mississippi, but use of a sterile triploid is highly recommended. For more information, request Extension Publication 1894 from your county agent.

Chemical Control -- Herbicides are a convenient but expensive means of controlling aquatic weeds in most cases.

Before you try any herbicide, you must accurately identify the aquatic weed. You must choose the correct and most economical herbicide and the proper treatment rate. Make an accurate measure of the water volume or surface area to be treated. Extension Information Sheet 673 gives procedures for calculating the amount of herbicide to use.

No control or inadequate control of an aquatic weed means that you selected the wrong herbicide, used an inadequate treatment rate, chose the wrong formulation, or improperly applied the herbicide. Excessive use of a herbicide, use at the wrong time, or use of the wrong material can result in a partial or total loss of all fish in the body of water treated.

Always read and observe label precautions before using any herbicide in an aquatic environment.

Follow these steps in aquatic weed control:

  1. Identify the problem weed.
  2. Choose the most economical and efficient control method.
  3. If you select a chemical method of control, be sure it is both economical and safe as well as effective.
  4. Calculate pond area and volume to be treated.
  5. Follow label instructions.

Revised by Dr. Martin W. Brunson, Extension Leader, Department of Wildlife and Fisheries.

Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.

Information Sheet 1036
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director

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