Flowers and shrubs are beginning to bloom, and pond owners may also be noticing signs of life too, in the form of filamentous algae and other aquatic plant growth.

Aquatic plants have an important role in the pond ecosystem. They produce the majority of dissolved oxygen for use by fish and other aquatic animals. These plants also serve as escape cover for young fish and provide food for some aquatic animals. As a rule of thumb, a pond supporting a population of fish should have aquatic plants covering about 20 to 40 percent of the surface area. However, problems arise when plants become so numerous in a pond that they interfere with fishing, boating or swimming.

The spring months are a good time to begin monitoring your pond for vegetative growth. The cooler water temperatures of late spring also provide more appropriate conditions for vegetation control, than do the hot months of the summer, especially when chemical control is used. In additional to chemical control, aquatic vegetation can also be managed through mechanical and biological techniques.

Chemical control is probably the most common approach that is used. If you are going to use chemicals to control aquatic vegetation, this should be done early in the growing season, and no later than July 1^st. If herbicides are applied after this date, special techniques must be used or you may cause a fish kill, because as the water temperature rises in a pond, it holds less dissolved oxygen. When aquatic plants are killed during warm water conditions, oxygen levels drop even lower, because the decomposition process uses some of the dissolved oxygen. The resulting low oxygen level could cause a fish kill in the pond.

Chemical recommendations and application methods vary depending on: the type of aquatic plant, uses of the pond's water, and the condition of the water. It's best to contact a district fisheries biologist with the Illinois Department of Natural Resources for your specific situation. Remember to always read and follow label directions when using chemicals. In addition, aquatic chemical application to ponds held in joint ownership, such as subdivision ponds, requires a commercial aquatic pesticide applicator's license.

Mechanical vegetation control involves the physical removal of the plants. Emergent plants such as cattail and arrowhead can be removed through pulling by hand when they first begin to grow in the spring. The mechanical removal of submergent vegetation and filamentous algae requires more time and effort. This involves raking or dragging the pond to remove the vegetation. Although this method is very labor intensive, it can be an effective, non-chemical method for removing vegetation from small areas, such as swimming areas or beaches.

Biological control, using triploid grass carp, is a third method of control. Triploid grass carp eat submerged vegetation, but will not eat emergent plants, such as cattail, and they will not eat algae. Therefore, the use of triploid grass carp is not a cure-all and a fisheries biologist should be contacted to determine whether this technique is suited for your situation. Correct stocking rates are also critical to this option so that all of the submerged vegetation is not removed from the pond, which can lead to potential algae problems. Biological control can also be accomplished during pond construction by minimizing the area of pond that is less than 3 feet deep. This will reduce the suitable habitat for many aquatic plant species.

Aquatic plant management takes careful thought and planning, so start now. Pond management and aquatic vegetation management publications from the Illinois Department of Natural Resources are available at the following website: http://www.ifishillinois.org/. If you have questions about pond management, contact University of Illinois Extension ChampaignCounty at 333-7672.