Aquatic Weed Control

Intro   |   Identifying Weeds   |   Controlling Weeds   |   List of Common Weeds   |    Control Methods

• Biological Control
• Physical Control
• Chemical Control
• Mechanical Control
• Grass Carp

Grass Carp

Click here for a printable version of this publication: Aquatic Weed Control: Using Grass Carp

The table below lists plants that grass carp typically control. If the species of plants they want are not available, carp feed on new growth of less-desirable plants and on plants above the water surface. It is this strong appetite for plants that makes grass carp useful in controlling aquatic weeds.

Common name	Scientific name	Preference	Effectiveness
Algae - Filamentous	Spirogyra sp., many others	Moderate	Low
Algae - Muskgrass	Chara sp.	High	High
Algae - Planktonic	Many species	Low	Low
Algae - Stonewort	Nitella sp.	High	High
Alligatorweed	Alternanthera philoxeroides	Low	Low
American lotus	Nelumbo lutea	Low	Low
Arrowheads	Sagittaria sp.	Moderate	Low
Bladderwort	Utricularia sp.	High	High
Bulrush	Scirpus sp.	Low	Low
Burreed	Sparganium sp.	Low	Low
Bushy pondweed, Naiad	Najas sp.	High	High
Cattail	Typha sp.	Low	Low
Coontail	Ceratophyllum sp.	High	High
Duckweed	Lemna sp., Spirodella sp.	High	Low
Eelgrass	Vallisneria americana	Low	Low
Elodea	Egeria densa	High	High
Eurasian water milfoil	Myriophyllum spicatum	Moderate	Moderate
Fanwort	Cambomba caroliniana	High	High
Frogbit	Limnobium spongii	Low	Low
Hairgrass, Slender spikerush	Eleocharis acicularis	Moderate	High
Hydrilla	Hydrilla verticellata	High	High
Parrotfeather	Myriophyllum aquaticum	Moderate	Moderate
Pondweed	Potamogeton sp.	Moderate	Moderate
Sedges	Cyperus sp.	Low	Low
Smartweed	Polygonum sp.	Low	Low
Spatterdock, Yellow cow lily	Nuphar sp.	Low	Low
Spikerush	Eleocharis sp.	Low	Low
Water cress	Nasturtium officianale	Moderate	High
Water fern	Azolla caroliniana	Moderate	Low
Water hyacinth	Eichornia crassipes	Low	Low
Water hyssop	Bacopa	Moderate	Low
Water primrose	Jussiea sp.	Low	Low
Watermeal	Wolffia sp.	High	Low
White waterlily	Nymphaea odorata	Low	Low
Willows	Salix sp.	Low	Low

 

The number of grass carp required to control weed problems varies, depending on the degree of weed infestation, kind of weed, size of pond or lake, and size of fish stocked. The general rule in farm ponds is to stock enough grass carp to control the weeds in one to two seasons but not so many that they quickly eat all vegetation. The best approach is to consider the grass carp as a weed maintenance tool rather than a total elimination tool.

For most farm pond situations where weeds have already become a problem, 5 to 10 grass carp per surface acre usually achieve desired weed control. In ponds with severe weed problems, higher rates of 15 to 20 grass carp per acre may be necessary for plant control. In such cases, it is sometimes more effective to treat the pond chemically with an herbicide first, and then stock moderate numbers of grass carp to prevent weed regrowth. You can get assistance in diagnosing the situation by contacting your county Extension agent or a fisheries biologist from other state or federal agencies.

In new ponds where you stock triploid grass carp for weed prevention, five fish per acre usually is sufficient. Grass carp are very good at preventing weed establishment, and even eat nonpreferred plant species when they first begin to grow and are still soft and tender. In new ponds, fingerling triploid grass carp may be successfully stocked anytime before the bass are stocked. Once bass are present, however, you must stock triploid grass carp that are at least 8 inches long to ensure bass cannot eat them. Although this size fish costs more, larger fish are necessary for them to survive.

Although regular “diploid” grass carp will not reproduce in ponds, they may reproduce if they are washed downstream into rivers. They can have environmental impacts on native plants and animals, so many states have restricted or prohibited the use of grass carp. They are not permitted for control of plants in farm ponds in Mississippi. Triploid grass carp are sterile, so they cannot reproduce if they escape into the wild. Only triploid grass carp should be stocked in Mississippi ponds.