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 20 to 40 percent of the surface area. Problems can arise when plants become so numerous in a pond that they interfere with fishing, boating or swimming.

If you have an existing pond that has aquatic plants interfering with the pond's intended use, there are several management options, which include mechanical, biological and chemical control.

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 caused by low oxygen levels. As the water temperature rises in a pond, its capacity to hold dissolved oxygen decreases. If large quantities of aquatic plants are killed during warm water conditions, the pond's oxygen level may become even lower as decomposing plants use additional 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 through raking or dragging the pond. 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.

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.

Aquatic plant management takes careful thought and planning. To learn more about pond management, a seminar is scheduled for April 16^th from 7:30 to 9:00 pm at the Crystal Lake boathouse. The seminar is cosponsored by the Champaign County Soil and Water Conservation District and will be presented by Mike Garthaus, Illinois Department of Natural Resources fisheries biologist and Dave Shiley, University of Illinois Extension. On April 18^th at 1:30 and again at 7:00 a teleconference presentation focusing on aquatic plant management will be conducted at the University of Illinois Champaign Extension Unit. If you would like to attend any of these upcoming events contact the University of Illinois Champaign Extension Unit at 333-7672 to register.