Aquatic Weeds

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Plants are needed in aquatic habitats to help provide oxygen to other aquatic species, but they can grow so quickly that they can negatively affect the pond. They are then referred to as aquatic weeds. Aquatic weeds can interfere with swimming, fishing, or other recreational activities if not controlled. Since water temperatures are warming up, pond owners may start to notice weeds growing they hadn’t noticed before.

Around this time, I start receiving phone calls about how to identify aquatic weeds. Some of the most common weeds I have seen growing in ponds around the county are Duckweed, Proliferating Spikerush, Bladderwort species, Pondweed species, and several algae species. Aquatic weeds can be divided into six groups: algae; free floating; floating rooted; submersed; shoreline; and grasses, sedges, and rushes. Properly identifying the weeds is the first step in controlling the weeds. Control methods are usually species specific, so knowing what type of weed is critical. Biological, mechanical, and chemical control are ways to reduce and/or control aquatic weed growth.

Biological control of aquatic weeds usually refers to the stocking of grass carp. Grass carp are sterile fish that cannot reproduce and primarily feed on submersed plants. The amount of grass carp to stock will depend on the size of the pond and the extent of the weeds. The general rule of thumb is 10 to 15 grass carp per acre and bigger than 10 inches in size to prevent predation by larger fish.

Mechanical control involves harvesting the weeds by hand or machine. Mechanical control has both advantages and disadvantages. The advantages are that decaying weeds can be removed and it eliminates the need for herbicides, which can have water-use restrictions. The disadvantages are that it can be time consuming to remove and vegetation can be dispersed elsewhere in the pond.

Chemical control involves the use of herbicides to remove unwanted aquatic weeds. There are many different herbicides labeled for aquatic use. ALWAYS read and follow the directions, taking special notice for water-use restrictions.

A publication entitled Weed Management in Small Ponds that gives the effectiveness of grass carp and herbicides on aquatic weeds is available through Cooperative Extension; you can request a copy by calling 910-671-3276. If you have any questions or need help identifying aquatic weeds or an appropriate herbicide, please contact Taylor Chavis, Extension Livestock Agent with North Carolina Cooperative Extension, Robeson County Center, at 671-3276, by E-mail at, or visit our website at North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.