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Single-celled algae, usually not visible, form the base of the food chain and make much of the oxygen needed for other life in the pond. Filamentous algae, sometimes called moss or grass, is more visible and most easily becomes a nuisance. Sudden growth of either type of algae is called a “bloom”.
Rooted aquatic plants are important to the overall health of ponds and lakes. They stabilize the shoreline and pond bottom, tie up plant nutrients thus reducing algae blooms, help the water to clear faster after a rain, produce oxygen and provide food and habitat for the many forms of life that live in and around a pond. Plants also provide nursery habitat for many fish and moderate levels are important for good growth, condition, and abundance of sport fish. Research shows that lakes without rooted plants may not have balanced, desirable fish populations.
Plant ControlRooted plants are necessary for a healthy pond, but too many can upset a fishing pond’s balance and become a nuisance. Everyone has different tolerances to pond plant life. Most biologists agree that once the plants cover over 40% of the surface area of a pond, they are over-abundant. There are four plant control options: preventative, mechanical, biological and chemical.
Managing the watershed and deepening the shoreline are preventative and are easiest and most effective to use before the pond is built. Conservation practices like silt retention structures, wetlands, buffer strips and grass waterways in the pond’s watershed keep soil and plant nutrients from reaching the water. Deepening shorelines create smaller areas where sunlight can reach the pond bottom, reducing the area that rooted plants will grow. Any number of livestock in a pond’s watershed can overload a pond with plant nutrients over time; steps should be taken to divert or contain animal waste products.
When preventative measures are not practical, mechanical methods like hand removal, bottom blanketing, shading, and water draw-down can be effective for short-term control. Removal can be done any time of the year. Remove plants by hand, with a rake or by dragging a light wire lattice or steel frame. Many aquatic plants can root from fragments, so be careful to remove all plant stems that float up. Once plants are removed from high-use areas, blanket the pond bottom with sand or gravel to slow plant re-growth. Small areas can be blanketed for 30 days with thick black plastic (punctured to allow gasses to escape) or commercial weed barrier products held with a frame or weighted at the corners. Pond dye products that reduce light penetration can shade the whole pond. Apply these products early in the growing season; they often need to be re-applied later in the season. Winter drawdown methods expose these dewatered areas to freezing and drying for several weeks through the winter to kill underwater plant roots. Not all kinds of plants can be controlled by this method; it is most effective at controlling species like Elodea, milfoil, coontail and lilies. Pondweed (i.e. Potamogeton) naiad, hydrilla and seed-producing species are not effectively controlled by drawdown. Leave at least eight feet of water depth in the pond to avoid killing fish over a long, snowy winter.
Biological control with grass carp (white amur) can provide effective, long-term control for underwater plants, but will not control algae or shoreline plants like cattails. Stocking too many grass carp can increase the growth of algae and nearly eliminate all aquatic vegetation. Carp are difficult to remove and can live beyond 20 years. The automatic stocking of grass carp is not recommended for aquatic plant control in new ponds. Use a conservative stocking of 1 to 2 fish per acre for heavy plant growth. These fish should be 10 inches or longer to avoid being eaten by largemouth bass. Be patient, vegetation control may not be noticed for 2-3 growing seasons after stocking. Additional stocking may be needed if no control is seen, or if plant growth returns to nuisance levels.
Chemical control with herbicides is another method for seasonal control of aquatic plants. Follow these five steps with any herbicide application:
There are several drawbacks to using herbicides to control plants. Control can be ineffective if treatment is applied at the wrong time of year (read the product label for best application times). When there is a large area of vegetation to kill, the decay of all these plants can use much of the oxygen in the water and cause a fish kill. Divide large areas of vegetation into smaller areas to prevent a fish kill. Treat the smaller areas several weeks apart, especially in summer months when plants decay faster and the water holds less oxygen due to warmer water. Control can be temporary and expensive and repeated applications may become necessary. Some herbicides require that selected pond uses stop for a period of time after application. Find an excellent overview of which herbicides will work for different plant types in the Iowa State University Fisheries Extension Service publication Aquatic Plant Management or at the Aquatic Ecosystem Restoration Foundation website. You can also call your local fishery management biologist for help.
Depending upon the level of plant growth, the types of plants present and the intended use of your pond, it may be helpful to use several control methods to get the desired results. For example, hand removal or herbicide control with bottom blanketing in high-use areas with a light stocking of grass carp may work better than any one of these methods alone.
Aquatic plants usually become established in a pond without special effort, but some plants are less likely to become a nuisance for anglers or other pond uses. Introducing a variety of these plants can help you meet your pond management goals more quickly. A new pond is like a newly tilled field or garden, something will grow there with nutrients, light and seed. Shoreline species that grow above the water surface suggested for ponds include: arrowhead, pickerel weed, spike rush, sweet flag and water iris. Floating-leaved lilies can be a nice addition to ponds without extensive shallow areas. (Don’t confuse the preferred lily with lotus, which spreads aggressively and would not be a good choice for a pond.) Wild celery and water stargrass can add to the diversity of plants that grow completely under the water. Largeleaf and longleaf pondweed have both underwater and floating leaves. Avoid introducing milfoil (could be the invasive Eurasian milfoil), naiad (invasive brittle naiad), curly-leaf pondweed (invasive), cabomba (invasive submersed plant common in water gardens) and coontail (will colonize on its own).
Growth form: Emergent (E), floating-leaved (F), submersed (S) * Is itself an invasive species or closely related
Purchase aquatic plants from a local nursery or one in a climate zone similar to your pond’s location. A pond plant identification guide can help you identify the plants growing in your pond so you can properly manage them.
Introducing plants in new ponds is a little easier than in existing ponds that already have established plants. Remove the aquatic plants from an existing pond that are growing in the area where you will introduce new plants (see mechanical or chemical removal below). Protect your plantings behind a small, protective fence/cage until they become established to prevent them from being eaten by grass carp or common carp, muskrats, turtles, waterfowl or deer.
Plant 5-20 plants per area to increase plant establishment success . Shoreline plants do best when planted at the water’s edge or in very shallow water. These can be moved using small plugs from patches found growing within the pond. Floating-leaved and underwater species can be planted in water from 6 inches to 2-3 feet deep. There is no need to plant deeper than you can easily reach.