Pond Herbicides for Algae Weeds

Pond Herbicides for Algae Weeds

Ponds are no stranger to unwelcome weeds, which grow rapidly and can ruin the beauty of your pond. Algae are among the most popular aquatic weeds and may lead to problems, according to Purdue University. An abundance of algae growth may lead to the passing of seafood and desirable aquatic plant life. You can use herbicides to help control algae, as well as other annoying aquatic weeds.

Copper Sulfate

Copper sulfate has been utilized to control algae and other aquatic weeds. This contact herbicide is toxic to fish and other aquatic wildlife, so use it with extreme caution to prevent unintended injury to desirable aquatic life. Trout, white armur and ornamental goldfish — such as koi — are sensitive to copper sulfate, so use something different in ponds using this particular fish. The toxicity and effectiveness of copper sulfate relies heavily on the alkalinity level of the pond. If copper sulfate is added to ponds using a 50 parts per million alkalinity level or reduced, its toxicity level rises and fish species that could generally endure this herbicide might die. Testing the water’s hardness before inserting herbicides will prevent injury to fish.

Sodium Carbonate Peroxyhydrate

Though it doesn’t destroy the algae, sodium carbonate peroxyhydrate inhibits algae growth and prevents blossoms from forming. This algaecide is effective as a preventive measure against filamentous algae and blue-green algae, also called cyanobacteria. Sodium carbonate peroxyhydrate comes in a granular form that — when added to the water — breaks down into hydrogen peroxide and sodium carbonate. This creates an oxidizing agent that controls algae. Since some algae strains can become resistant to copper, sodium carbonate peroxyhydrate is an alternate method to controlling algae in ponds previously treated with copper sulfate.


Diquat is a contact herbicide that controls aquatic weeds including Pithophora and Spirogyra filamentous algae. This non-selective herbicide works best when applied to the pond before the algae has attained the surface. Muddy water deactivates the active ingredient in diquat, which will reduce its effectiveness. Diquat is only slightly toxic to fish and if you stick to the recommended application rate is followed, then you reduce the potential for harming aquatic life. However, as the aquatic weeds decay, the oxygen level in the pond water starts to deplete. Without the proper oxygen levels, fish might not survive. Employing strip software of diquat can help prevent injury to fish.


Endothall-amine salt is a contact herbicide and algaecide that controls blue-green algae and filamentous algae. Even in low levels, endothall could be lethal to fish. The Ohio State University recommends applying endothall in the pond coastline and working outward to reduce the possibility of fish death, although this might not operate at a small, backyard pond. This will allow the fish to retreat from the herbicide-treated places. Endothall works best when the water temperature is 65 degrees Fahrenheit or higher. Do not use this herbicide in water used for irrigation.

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