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Filamentous Algae

Spirogyra, Anabaena, Oscillatoria, Lyngbya, Pithophora spp., etc.

Management Options

Mechanical/Physical Control Options

Filamentous algae can be racked or seined from the pond.

Fertilization to produce a phytoplankton or algal “bloom” can prevent the establishment of filamentous algae if started early enough in the spring. Fertilization also produces a strong food chain to the pond fish.

Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Aquashade, Blue Springs, and Crystal Blue are examples of non-toxic dye and other products are available. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.

Many types of mechanical removal devices are available that cut or chop up aquatic weeds. It is important to remember that many submerged plants regrow from fragments, so removal of cut fragments many be necessary to keep from spreading the unwanted plant. Companies that make cutters and rakes include but are not limited to Cutting Edge, Jenson Lake Mower, Midwest Aqua Care, and WeedRoller.

Physical barriers are also used to eliminate plants by shading the bottom. These work well for swimming areas, docks, etc. but must be kept clean of any buildup of sediment and debris. Lake Mat and Lake Bottom Blanket are examples of companies that makes these mats.

Biological Control Options

Grass carp will seldom control aquatic vegetation the first year they are stocked. They will consume filamentous algae but is not a preferred food item. Therefore, they will usually consume other types of submerged vegetation before they consume filamentous algae. Grass carp stocking rates that will control filamentous algae are usually between 10 and 20 per surface acre. In Texas, only triploid grass carp are legal and a permit from the Texas Parks and Wildlife Department is required before they can be purchased from a certified dealer (list at the end of the packet).

Tilapia will consume filamentous algae but are a warm water species that cannot survive in temperatures below 55ー F. Therefore, tilapia usually cannot be stocked before mid-April or May and will die in November or December. Recommended stocking rates are 15 to 20 pounds of mixed sex adult Mozambique tilapia (Oreochromis mossambicus) per surface area. Tilapias are often not effective for vegetation control if the pond has a robust bass population due to intense predation. In Texas, stocking of Mozambique tilapia does not require a permit from the Texas Parks and Wildlife Department. Any other species of tilapia would require a permit. Check with out County Extension Agent in other states for legality of stocking tilapia.

Chemical Control Options

The active ingredients that have been successful in treating filamentous algae include copper based compounds (E), alkylamine salts of endothall (G), sodium carbonate peroxyhydrate (G), and diquat (G). E = excellent, G = good

Copper Sulfate or “blue stone” is probably the most commonly used algal treatments because of its availability and low cost. Copper sulfate comes in several forms depending on how finely it is ground. Smaller crystals will dissolve easier than larger crystals. In very hard water it is difficult to use copper sulfate because it binds with the calcium, precipitates out of solution, and renders the copper ineffective as an algaecide.

All copper compounds can be toxic to fish if used above labeled rates and can be toxic in soft or acidic waters even at label rates. Before using copper is it best to test the pond water’s alkalinity and adjust copper treatments to alkalinity concentrations. For additional information on using copper sulfate see the SRAC #410 Calculating Treatments for Ponds and Tanks.

Cutrine Plus, K-Tea, Captain, and Clearigate are all chelated or compound copper herbicides that are effective on filamentous algae. Other chelated or compound copper formulations are available but are not linked to this web site.

Hydrothol 191 is an alkylamine salt of endothall which can be used to control filamentous algae and comes in liquid and granular formulations. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact. Hydrothol can be toxic to fish.

GreenClean, PAK27, and Phycomycin are Sodium Carbonate Peroxyhydrate based herbicides. These are pelleted contact herbicides for control of blue-green algae. Hydrogen peroxide is the active agent in this algaecide. It is not effective on the macroalgaes, Chara or Nitella, or on any higher plants.

Reward is the registered diquat label for aquatic use and has been found effective on filamentous algae. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.

One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.

Many aquatically registered herbicides have water use restrictions (See General Water Use Restrictions).

To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.

Cultivation Options

Filamentous algae are seldom encouraged. It could be encouraged by transplanting mats of filamentous algae from another pond and not fertilizing to encourage a planktonic algae bloom.