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|The most common aquatic weed problem in many ponds is filamentous algae.
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Controlling Filamentous Algae in PondsThe most common aquatic weed problem in many ponds is filamentous algae. Its presence can degrade water quality and recreational enjoyment. Excessive algae can cause an oxygen depletion leading to a fish kill when it decomposes as a result of natural die-off or herbicide application. Early and regular control measures will help reduce the problems associated with filamentous algae.
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Reference: Ohio State University Extension
There are many species of filamentous algae and microscopic examination is usually required to make an exact identification. However, some of the more common forms can be distinguished by their texture. Spirogyra is bright green and slimy to the touch; Cladophora has a cottony feel; and Pithophora is often referred to as "horse hair" algae because its coarse texture resembles that of horse hair and it may feel like steel wool.
Steepening the sides of the pond to achieve a 3:1 slope will eliminate shallow water areas so that sunlight cannot reach bottom-growing algae. However, if the entire pond has filled in as a result of sedimentation or decaying vegetation, a dragline or dredge may be needed to deepen the pond.
One method of biological control is maintaining a fertility level that fosters the development of a microscopic plant and animal population, which prevents sunlight penetration. This requires intense management and more time than the average pond owner may wish to devote to the pond. Sunlight penetration to the pond bottom where the algae begins to grow can also be reduced by introducing an inert dye (usually blue).
The addition of triploid white amur (a vegetation-eating fish) as a biological control measure may have mixed results. Filamentous algae is not a preferred food, but will be eaten if no other vegetation is present. If other aquatic plants such as water milfoil or coontail are readily available, the filamentous algae may be ignored and continue to flourish.
The method of application will determine what size of copper sulfate crystals to purchase. The important principle to keep in mind is that actual contact of the copper sulfate with the algae is necessary in order to achieve satisfactory control. For best results, dissolve copper sulfate in water and spray it directly on floating algal mats or on the water surface above submerged algae. Finely ground, "snow grade" copper sulfate is best for1 this method as it dissolves easier. Mix the desired amount of copper sulfate with enough water to cover the area to be treated, and apply with a sprayer or bucket and dipper. Because copper is corrosive to galvanized metal, application equipment and mixing containers should be made of plastic or stainless steel.
In large ponds and when spray equipment is not available, it may be easier to treat with copper sulfate by placing the larger crystals of this chemical in a burlap bag and towing the bag through the water until all the crystals have been dissolved in the area to be treated.
One application of copper sulfate is unlikely to provide season-long control. Re-treatment may be necessary at 3-4 week intervals.
There are no water-use restrictions associated with the use of copper sulfate. When applied at the proper rate, the water may be used immediately for swimming, drinking, fishing, irrigation and livestock. However, since copper sulfate has a metallic odor, pond owners may want to suspend drinking, swimming and livestock watering uses for 12 hours.
Pithophora is extremely difficult to control. Its unique cell wall structure and the tight clumping of filaments inhibit the penetration by copper. Additionally, large numbers of resilient spore-like bodies, called akinetes, germinate and provide a continuous source of new plants. Partial, short term control can usually be achieved with either of the following herbicide mixtures:
Additionally, Cide-Kick, a nonionic spray adjuvant, should be added to the mixture at the rate of 1-2 gallons per surface-acre. This material acts as a cell wall penetrant to increase the effectiveness of the herbicides.
Copper sulfate is corrosive to galvanized containers. Therefore, the solution should be mixed in wooden, earthenware, plastic, stainless steel or copper-lined containers. If a sprayer is not available, you may broadcast the solution with a plastic watering can or bucket and dipper.
If the algae is so abundant that it covers more than half of the total pond surface, a complete treatment may result in an oxygen depletion and fish kill. This hazard is greatest during very hot, overcast weather. When these conditions exist, treat only half the pond and wait 10-14 days before treating the other half.
Copper compounds applied at the recommended rates are lethal to fish eggs and some species of newly hatched fish. These materials should not be applied during spawning periods, unless it is desirable to destroy the eggs and the new hatch. Bass will begin to construct shallow depressions in the pond bottom when the water reaches 60 degrees F. Eggs are deposited by the female and guarded by the male for 3-14 days. Within a couple of weeks after the bass have spawned and when the water temperature reaches 70 degrees F, bluegill and redear sunfish will be seen building nests in the shallow areas. As with the bass, the male guards the nest after the eggs have been deposited. These eggs will hatch in a few days. Bass will only spawn once in the spring, but forage fish (bluegill, redear sunfish and minnows) will spawn throughout much of the summer and some individuals may spawn several times in a single season. To avoid the application of copper compounds during the spawning season, monitor the water temperature and look for active nests in the shallow areas of the pond.
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|Data Source: Ohio State University Extension. Articles and resource may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide and it is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used.|