By Rich Clayton
Fisheries and Aquaculture Specialist
Iowa State University Extension
Spring is the time to consider your aquatic vegetation management plan for your pond. The excessive vegetation that was in your pond last year is easier to control when the water temperature is cool and the plant mass is small, thus reducing chances of causing oxygen depletion and fish kill.
Moderate plant growth is essential to water bodies because plants produce oxygen, food and cover for fish and other aquatic organisms. Nutrients and fish feeds introduced into the water (often from the surrounding watershed) can create an ideal habitat for aquatic weed growth. Aquatic vegetation is considered excessive when more than 20 to 30 percent of the pond surface is covered. Excessive vegetation may hinder fishing and cause water quality problems.
Aquatic vegetation may be in four forms
(1) Algae – primitive plants without true leaves or flowers. Many are free, in strings or clumped together, resulting in pea green soup coloration.
(2) Free floating plants – not attached to the bottom. Duck weed is one example.
(3) Submerged plants – attached to the bottom and growing below
the surface. These plants may be called “seaweed,” “moss” or “water grass.”
(4) Emergent plants – rooted to the bottom and extending beyond the surface. Common emergent plants are cattails, bulrushes, water lilies, smartweed and willows.
Three methods of vegetation control: mechanical, biological, and chemical
Most mechanical methods are costly and yield poor results.
Biological control can be achieved by stocking grass carp, an exotic fish native to southeastern Asia, or by restricting nutrient input into the pond. Please note -- grass carp are not allowed in all states (they can be used in Iowa) and they control rooted plants much more than algae. They are stocked at three to four 8-inch fish per surface acre of water. Because these fish do not reproduce in ponds and have low natural mortality, you may not need to restock for eight to ten years. Several private fish hatcheries in Iowa sell grass carp.
Chemicals may be used to control aquatic vegetation. Best results are obtained with proper identification of the vegetation that needs to be controlled, proper application time and using a suitable herbicide. In Iowa, chemical applications are best done in the spring before water temperatures increase. Before using any chemical, determine all possible uses for the pond. Many herbicides will make the water undrinkable for livestock and humans. Use only chemicals designed and approved for aquatic use. Chemicals are available from local agri-chemical distributors. Read and carefully follow all label instructions.
A great resource for aquatic plant management is http://aquaplant.tamu.edu/. It is based at Texas A&M University, where they have many of the same plants and control practices that we have and use in Iowa. Their Web site has many pictures to help with proper identification and management recommendations.
Additional information can also be found at ISU Fisheries Extension, www.nrem.iastate.edu/extension/fisheries/index.html
This article is from the May 2008 issue of Acreage Living.
Other articles in this month’s issue--
Spring Flood Preparedness
Grazing Management for Improved Pasture Production
Squinnies, Grinnies, and Gophers - Oh, My!