Filamentous algae are single algae cells that form long visible chains, threads, or filaments. These filaments intertwine forming a mat that resembles wet wool. Filamentous algae starts growing along the bottom in shallow water or attached to structures in the water (like rocks or other aquatic plants). Often filamentous algae floats to the surface forming largemats, which are commonly referred to as "Pond scums." There are many species of filamentous algae and often more than one species will be present at the same time in the pond.
Filamentous Algae Control Options
Filamentous algae can be raked 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. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.
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.
Tilapia will consume filamentous algae but are a warm water species that cannot survive in temperatures below 55°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 a County Extension Agent in other states for legality of stocking tilapia.
The active ingredients that have been successful in treating filamentous algae include copper based compounds (E), sodium carbonate peroxyhydrate (G), and diquat (G). E = excellent, G = good
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Products to Control Filamentous Algae
GreenClean is a Sodium Carbonate Peroxyhydrate based herbicide. These contact herbicides are used 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. GreenClean is the safest algaecide on the market for use around fish.
Redwing is a liquid diquat formulation that has been effective on coontail. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact.
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