Plant Image Gallery: Management

Goals and Objectives
Before deciding how to manage aquatic vegetation, a manager must identify the dominant species and learn whether they benefit or contradict the goals for the body of water. Some common goals or objectives include fishing, waterfowl hunting, water for livestock, irrigation, water sports and aesthetics. The amount of vegetation that’s tolerable varies, depending on the goals and objectives.
For most bodies of water, aquatic vegetation management begins with design. This is the easiest and most effective long-term management option. Water depth and slope of the banks help predetermine the amount and type of vegetation that can occur. If less vegetation is desired, design the body of water with slopes greater than 33% and most water depth greater than 6 feet to decrease the amount of shallow areas because most native plants have depth limitations. If waterfowl management is a goal, primarily shallow areas are desired to encourage more vegetation. For many ponds with fishing and livestock goals, a 3:1 (33%) slope down to 4 feet of depth is a common design criterion.
Mechanically managing aquatic vegetation is probably the most labor-intensive option. This technique typically involves the use of rakes, seines, tractors or harvesters. These techniques are usually temporary because many plants reestablish from fragments, roots or seeds. Mechanical treatment is most often used in small areas when chemical and biological treatments are not viable options.
Biological management can be a very effective tool. Biological management techniques include the use of grass carp, tilapia, goldfish, livestock and certain types of insects. Stocking grass carp is the most common biological management tool used for long-term control in ponds. Check local state laws pertaining to stocking grass carp. To protect the investment in grass carp and downstream waterways, install parallel-bar barriers on spillways and overflow pipes. This provides effective and predictable control. Grass carp have food preferences for certain plants. Depending on the amount and type of plants present, the appropriate stocking rate can vary. Commonly, five to nine grass carp per surface acre provide partial control, whereas 10 or more grass carp per surface acre usually provide complete control of the species that they consume. It is easier to add more grass carp than it is to remove them, so initial stocking should be conservative. If desired control is not met after two years, add one to two grass carp per surface acre. Grass carp can live for over 20 years, so control is long lasting. Certain species of tilapia consume various plants and goldfish consume algae, but they have their limitations for use. Tilapia are warm-water fish and typically do not survive in water less than about 55 degrees Fahrenheit, so they usually have to be restocked each spring. Goldfish can be effective, but they also increase clay turbidity, which generally contradicts other goals such as attracting waterfowl, aesthetics or sportfishing. Small goldfish also do not persist well in waters with abundant predators, such as largemouth bass. Livestock are used to control some emerged aquatic vegetation by consumption or trampling. However, they are mostly limited to plants around the shoreline. Insects have been used on some exotic and invasive plants, such as salt cedar and water hyacinth. The effectiveness of insects as a management tool varies with plant species, insect species and location, and is still being researched.
Aquatic vegetation can also be managed with chemicals. Herbicides are the most popular; however, almost all treatments are temporary and expensive. Herbicides tend to control certain species well and not others, which is why proper identification is so important. Associated risks with using herbicides include killing desirable species and creating a low level of dissolved oxygen. When using herbicides, treat early in the growing season when the nuisance plant occupies a small portion of the water body. Before using most herbicides, obtain an accurate surface area measurement and measure the average depth, so the volume of water can be calculated. Always read and follow the directions on the label. Dyes change the color and transparency of water, reducing sunlight penetration through the water, which prevents plant growth. Dyes are not effective on plants growing at or above the surface of the water. Fertilizers can be used to promote phytoplankton growth, which ultimately increases fish production. Increased phytoplankton reduces visibility through the water, producing similar results as a dye.
Aquatic vegetation is an important part of the ecosystem. Aquatic vegetation has both positive and negative attributes, but it is up to the manager to determine what role aquatic vegetation plays in relation to their goals or objectives. If management of aquatic vegetation is deemed necessary, choosing the appropriate method is essential. This information assists managers in making correct management decisions by providing the most basic need: proper identification.