July 11, 2001

Richard E. Bir
Ext. Horticulture Specialist
North Carolina State University

Copper use in irrigation basins (ponds in TN?)

The following information is from Tennessee Extension and serves as a reminder of many things. Please read Dr. Stratford Kay's publication on managing weeds in small ponds either before or after reading the information from Mark. Dr Kay's pub can be found at http://www.cropsci.ncsu.edu/aquaticweeds/ag-437.pdf>

Some things that Stratford suggests that you remember when talking to clients about using copper sulfate or one of the chelated copper compounds for algae control are that it is almost NEVER that more than a small part of a pond is treated at one time to prevent algal decomposition from dropping the oxygen levels too low for the fish. The maximum labeled rate for Cu ion in water (for an algicidal or macrophyte herbicide treatment) is 1.0 ppm. Dr. Kay has never heard of ANY situation where copper was applied as an algicide/herbicide where ANY crop damage has occurred (this is over 27 years in which he has been doing research in aquatic plant management).


by Mark Halcomb, University of Tennessee Area Nursery Specialist

Some types of algae can be killed in small ponds with a handful of copper sulfate in an old sock. It is a simple procedure, but there are several comments and precautions concerning this practical approach.

This easy solution is more effective on planktonic algae that may appear as green pea soup. It will control some types of filamentous algae, but copper sulfate will not control aquatic weeds, either submersed or floating. Actually, planktonic algae can stifle the more serious weeds by preventing their germination and growth by reducing light penetration. Commercial dyes are used to provide the same effect.

When copper sulfate crystals are spread over the water surface many settle to the bottom before they dissolve without killing the algae. The chemical becomes tied up with the sediment quickly and is rendered harmless. Dissolving the copper sulfate and spraying it onto the water surface is effective. But the sock method eliminates both the need for a sprayer and the time required for spraying. Placing the copper sulfate in a cloth bag or sock prevents it from falling to the bottom and becoming unavailable to kill algae. Tie the sock to a floating device and secure the float away from the pond edges. Use 1 sock for each half acre in a pond. The algae will be killed in a matter of hours. The water will clear. If nothing happens, refill the sock in a few days.

The water may turn brown or even grayish during the decay process if a lot of algae dies at one time. As mentioned earlier, clear water is not necessarily desirable. When the green algae growth returns, fill the sock. You will learn how to gauge the amount and frequency with experience. As long as there is a problem with algae, copper sulfate can be applied on an as needed basis, and as often as needed.

Aquatic herbicide rates are frequently expressed as amount per acre-foot of water. One acre-foot of water is one surface acre of water, one foot deep. For example, a 3 acre pond averaging 5 feet deep would contain 15 acre-feet of water. Another term to express treatment rates is parts per million (ppm). One ppm is 2.7 pounds of chemical (copper sulfate for example) per acre foot. A half pound of copper sulfate per acre foot would provide 0.2 ppm. Low rates of copper sulfate are safe for irrigation water, fish survival, fish consumption, livestock drinking and swimming. One ppm can kill fish in low alkalinity water. But remember, it binds with algae and sediment quickly, and does not stay around in the water very long. One pound per surface acre may kill enough algae and should not kill fish.

Concentrations greater that 0.2 ppm could be phytotoxic to ornamental plants. It would be best to apply the copper sulfate after the daily irrigation to allow time for the chemical to work on the algae. The concentration is reduced rapidly as it binds with the algae and sediment. The concentration would likely be safe the next day in time for the next irrigation.

Copper sulfate is considered safe for water used for irrigation, fishing, watering livestock and swimming. There are no restrictions placed on its use.

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