2007-03-28 / Farm & Home

Ag Line: Grass Carp for Pond Weed Control

By Wade Parker County Extension Coordinator

As spring arrives, we all get the urge to work in our gardens and yards. However, those of us with ponds will start killing weeds and fertilizing.

With the onset of warm weather, the weeds start growing in our ponds. Weeds in ponds can be controlled by herbicides or by biological control. The biological control I am referring to is the use of grass carp. Grass carp are sterile and do not root in the pond bottom. They are like cattle, as they will eat preferred plants first and then graze less desirable plants. Grass carp seem to prefer plants growing below the water surface and tender plants rooted to the pond bottom. Grass carp may be effective against duckweed and filamentous algae, but to control these two troublesome species, carp must be stocked at a higher rate. If too few fish are stocked, weeds will not be controlled; therefore, always stock high enough to allow for some mortality.


Spring stocking is best because as the water warms up, the plants begin to grow. As the plants begin to grow, they will be very susceptible to grass carp. Fall is also an excellent time to stock with grass carp too. The fish will get a good start in warm water and the weeds are abundant for fish consumption. Summer stocking is difficult due to the fact that handling and transporting fish during hot weather may reduce survival. As you stock your pond, stock fish large enough (12 inches or larger) to escape predation by bass, large catfish, etc. It may take a season or two for the fish to control aquatic weeds in your pond.

The two main weed species found in ponds in our area are duckweed and filamentous algae. The recommended stocking rate for algae control is 30 grass carp per acre, and the carp should be 12-14 inches in length. It may be useful to use a herbicide to reduce the amount of weeds prior to stocking with grass carp. Stocking your pond is not going to be a silver bullet cure for aquatic weed control, but plays an excellent part in your overall weed management program. The Jenkins County Extension Office has a list of grass carp suppliers and will be happy to provide this to you upon request.

The University of Georgia Cooperative Extension offers educational programs, assistance, and materials to all people without regard to race, color, national origin, age, sex or disability.
  Plants Usually Controlled
          by Grass carp
Naiad                   Bladderwort
Fanwort               Elodea
Hydrilla               Chara
Coontail               Parrotfeather
Pondweed             Duckweed

      Plants Sometimes
  Controlled by Grass carp
Filamentous Algae     Reeds
Cattails                 Watermeal
Bulrushes             Smartweed
Lotus                     Stonewort
Aquatic Grasses

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