Don’t wait to treat filamentous algae


Filamentous algae is the summertime problem that begins in early spring.

Sometimes, we realize we have an issue after the effective treatment period has already passed. For example, we walk the pasture finding weeds boot high or even taller. Or we notice our hay cutter is beaten to death by all the Fire ant mounds in the hay field. Early treatment when the culprits are starting is the best and most effective time to treat most of our common problems.

Most of our issues have an “optimal” treatment period and the case with filamentous algae is no different.

According to Texas A&M’s Wildlife and Fisheries website, “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 large mats, 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 has no known direct food value to wildlife. Submerged portions of all aquatic plants provide habitats for many micro and macro invertebrates (i.e. bugs, worms, etc.). These invertebrates in turn are used as food by fish and other wildlife species (e.g. amphibians, reptiles, ducks, etc.). After aquatic plants die, their decomposition by bacteria and fungi provides food (called “detritus”) for many aquatic invertebrates.

This algae begins growing in early spring but is most often noticed later down the line when it is already well established and far more difficult to control.

Several means of control are effective but the timing of these is important to their efficacy.

Filamentous algae can be raked or seined from the pond. Fertilization of the pond can produce a phytoplankton or algal “bloom” which can reduce sunlight penetration thus hindering the algae’s growth. The bloom has an added benefit of giving the food chain a boost and in turn boosting the fish population and health. Fertilization can be achieved simply by adding conttonseed meal to the edge of the pond about 2 feet in. the size of the pond determines how much. As a general rule 150-200lbs. to the acre is applied in early spring.

Non-toxic dyes or colorants are also available that act in the same way, by reducing sunlight penetration but again this must be done early in the spring to be effective.

A biological control is available by stocking Tilapia. Tilapia will consume filamentous algae but are a warm water species that cannot survive in temperatures below 55 degrees 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.

Tilapia 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.

Some chemical control options are also available but may require a private applicator pesticide license. Make sure to follow the label instructions as the “label is the law”.

Some examples of chemical controls are Copper Sulfate (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), Diquat, Alklamine Salts or Endotholl, Flumioxazin and Sodium Carbinate Peroxyhydrate.

Taking steps early helps to increase your success when controlling filamentous algae.

For more information about algae control in ponds or any other topic please contact the Madison County Extension office at (936) 348-2234.

Chadd Caperton is the Extension Agent for Madison County.