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Did you have mats of green hair-like algae floating on your pond last year? If so, that is filamentous algae, a common alga found in ponds. Filamentous algae begins growing in your pond on the bottom, and then floats to the surface as it matures.

Now is the time to scout for these algae. Use a garden rake and drag it along the bottom of the pond. It will be very bright green, with a slimy appearance. If you find it, the months of April and May are a good time to begin to controlling it, after the water temperature has reached 60 degrees Fahrenheit.

Copper sulfate is a contact herbicide used to control algae. Read the Label. Copper sulfate can cause burns on your eyes and skin, so read the label and wear the recommended personal protective equipment. The label will also tell you how much formulation to use based on the size of your pond, and since it is a contact herbicide, it must be dissolved in the water to be effective.

While the herbicide label will tell you the rate of application to use, that is only part of the information you will need. Do you know your pond’s size in acres to the nearest tenth of an acre? If not, you need to measure your pond, or you might ask your local Soil and Water Conservation District to calculate the surface acreage from an aerial photograph. Some aquatic herbicide application rates are based on the acre-foot volume of the pond.

Acre-foot volume is calculated by multiplying the surface acreage by the average depth of your pond. The average pond depth is best determined by taking several depth measurements across your pond in a grid layout, adding the depths recorded, and dividing by the number of measurements you took.

You may find other types of aquatic plant life during your scouting trips to the pond. It is very important to identify the plant, as this is the first step in selecting the correct aquatic herbicide to reduce the population. An Illinois Department of Natural Resources, IDNR fisheries biologist can help you correctly identify the plant and help with identifying control options. You can find a biologist by visiting .

Remember that aquatic plants have an important role in the pond ecosystem. They produce the majority of dissolved oxygen for use by fish and other aquatic animals. These plants also serve as escape cover for young fish and provide food for some aquatic animals. Problems may arise when plants become so numerous in a pond that they interfere with its intended use.

Aquatic plant management takes careful thought and planning, so start now. Pond management and aquatic vegetation management publications are also available from the IDNR at the previously mentioned website.

If you have questions or need assistance locating pond management resources, feel free to contact me in the University of Illinois Extension office located in Arthur at 217-543-3755.

For more information on University of Illinois Extension programming in Coles, Cumberland, Douglas, Moultrie and Shelby counties, visit our website at or call us at 217-345-7034.


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