Pond Algae and Aquatic Weed Control Information
If your pond is impacted by excessive algae and weed growth there are methods of treatment available to bring the growth under control. You may select chemical treatment or you may stock your pond with fish that feed on algae and weeds for a more natural method of control.
Vegetation in ponds may be classified as algae, floating plants, submerged plants or emergent plants. Before chemicals are selected for treatment, the type of vegetation to be controlled must be identified. The chemical Cutrine Plus can be used to control floating algae and Cutrine Plus Granular can be used to control bottom-growing algae.
Before other plants are treated it is important that you know what type of plant you plan to control. Chemicals such as Weedtrine II, Weedtrine D, Diquat, Aquathol K, Rodeo and 2,4-D are available and used by themselves or with Cutrine Plus to control undesirable plants.
If chemicals are selected it is important to keep several things in mind. It is absolutely essential that labels are followed. Some chemicals have a restricted use interval during which water should not be consumed by humans or livestock and fish should not be eaten. Since chemicals must be applied repeatedly beyond the initial treatment there is also a chance toxicity in soil and fish may build up in the pond over time. It is possible that the chemicals will also destroy those plants used as food supply by the fish resulting in a decline of fish population. Also, when algae and plants are killed by chemicals the decomposition process uses up oxygen in the water and this process may rob fish of essential oxygen, particularly during mid-summer. The best time for chemical treatment is in late spring and early summer.
If a more natural method of weed control is preferred, you may choose to introduce algae and weed eating fish to your pond. Triploid sterile grass carp have become the fish of choice for several weeds. Naiad, fanqort, hydrilla, coontail, various pondweeds, bladderwort, elodea and chara area species usually controlled with the triploid sterile grass carp. Plants that are not preferred by the grass carp include emergent, tough or woody stem species such as cattail, waterlily and rush. Filamentous algae, watermilfoil, Nitella and watershield are not controlled very well.
Only triploid sterile grass carp may be introduced onto Virginia waters for aquatic weed control. A permit must be obtained from the Virginia Department of Game and Inland Fisheries. An application may be obtained by a request [telephone (804) 367-8629]. The application includes maps of the area, type of weeds, size of the pond, water flow, number of fish required and means for containment of the fish. The application requires a $10 fee and a few weeks for granting approval. These fish may be stocked in relatively small impoundments where they can be contained readily. After receiving a permit, there are locations approved by the Department of Game and Inland Fisheries to purchase guaranteed triploid sterile grass carp. Cost is approximately $10 per fish.
Triploid sterile grass carp 10-12 inches long are stocked in ponds at the rate of approximately 7-15/acre. A fisheries biologist may visit the site before issuing a permit.
The Japanese KOI is known as an ornamental algae eater. These fish are brilliantly colored with the colors of the rainbow. A stocking rate of 24 per acre of pond will control algae. The KOI will not overpopulate a pond when Bass are present. Because of their vibrant colors, the young KOI are easily sought out and eaten by the Bass. The KOI live peacefully with other fish and can be trained to eat out of your hands.
Although the introduction of algae eating fish may have a higher start-up cost than chemical application, you should consider that the fish is a one-time cost while chemicals must be applied repeatedly. Another approach to biological control is to place up to four bales of barley straw per surface acre in shallow water around the perimeter of the pond.
Keep in mind that algae in ponds is usually a result of excessive nutrients in the pond water. Investigate the watershed that drains into your pond and see if you can identify ways to reduce nutrients reaching your pond. If crop fields area adjacent to your pond then a filter strip of thick fescue or other grass may help remove nutrients from runoff before it gets into your pond. If livestock or waterfowl (i.e. geese) have access, they may be directly depositing nutrients into the water. If the pond is located in an urban area then thought should be given to the amount of fertilizer used on gardens and lawns. Excessive application rates may be contributing to your algae problem. As with pond chemicals, the application rates on the fertilizer bags should be closely followed.
With proper management, pond algae and weed problems can be successfully brought under control. Feel free to contact us for information on how to locate suppliers at (540) 347-3120 extension 3.
The above information is taken from literature supplied by product dealers. The John Marshall Soil and Water Conservation District does not endorse or guarantee the products mentioned above. You are encouraged to contact the dealers of the products and discuss specific questions with them. If we can be of further assistance please contact us at (540) 347-3120, extension 3.
Date Last Modified: 05/03/2004