Chemical Control of Aquatic Weeds

Aquatic weeds in ponds or lakes can be controlled by physical removal, biological control, or herbicides. The method or combination of methods, used will depend on factors such as target weeds, non target plants, and the uses of the water (fishing, swimming, livestock watering, and irrigation).

Physical removal can be accomplished manually or with machinery. It is time consuming, expensive and normally used alone if other methods are not feasible. However, a certain amount of physical removal may be necessary in combination with the use of biological control and herbicides.

A free of charge permit from SC DNR is required to stock tilapia.

A free of charge permit from SC DNR is required to stock tilapia.
W. Cory Heaton, ©2015, Clemson Extension.

Biological control is an option for certain aquatic weeds. The major advantages are ease of application and no concern over damage to plants irrigated with treated water. Triploid grass carp can be very effective for controlling many submerged vascular aquatic weeds. Grass carp are usually used to control all vegetation in a pond, rather than selectively controlling certain vegetation. Replacement stocking of grass carp is necessary when fish are lost. A permit is required to stock grass carp, and only triploid fish can be legally used in SC. Tilapia are stocked in the spring and control most algae species. The concern with tilapia is that they are tropical animals and usually die during cold winters thereby requiring an annual stocking. Tilapia are legal for use in SC. The South Carolina Department of Natural Resources (SC DNR) now requires a free of charge permit to stock tilapia and triploid grass carp for aquatic weed control in SC. You can obtain a permit from SC DNR at 803-734-3891 or from registered dealers in SC. The short permit can be FAXed (803-734-4748) for a rapid turn around. A permit number from SC DNR is required prior to stocking tilapia and triploid grass carp. Check with your Department of Natural Resources to determine if grass carp and tilapia are legal to stock and if a permit is required in your state.

Imazypyr being sprayed to kill lily pads

Imazypyr being sprayed to kill lily pads.
W. Cory Heaton, ©2015, Clemson Extension

After spraying Imazypyr, there is a significant kill of waterlilies (Nymphaea odorata) on the pond.

After spraying Imazypyr, there is a significant kill of waterlilies (Nymphaea odorata) on the pond.
W. Cory Heaton, ©2015, Clemson Extension

2,4-D, carfentrazone ethyl, copper, diquat, endothall, fluridone, glyphosate, imazapyr, sodium carbonate peroxyhydrate compounds, and triclopyr are registered for use in ponds by US EPA and can be used safely in ponds if the manufacturer’s label directions are followed. Certain waiting periods may be required before certain water uses are allowed after the herbicide is applied, while in some cases waiting periods are not required. Various chemicals have different product formulations; only aquatic labeled pesticides and surfactants/adjuvants may be used in aquatic applications, by law. Labels change frequently; refer to the current herbicide label for specific application information. Never exceed the rates recommended on label of the specific product applied. The label is the law.

Amount of Formulation for Application

Herbicide Rate*
Aquathol 0.3 to 2.6 gal/acre foot of 4.2 L or 13 to 108 lb of 10G/acre foot or 2.2 to 22.0 lb of 63G/acre foot.
Hydrothol 0.3 to 3.4 gal/acre foot of 2L or 11 to 136 lb of 11G/acre foot.
Diquat 1 to 2 gal/surface acre of 2L.
2,4-D 1 to 2 gal/surface acre of 3.8 L or 150 to 200 lb of 20G/surface acre.
Copper Compounds 0.6 to 3.4 gal of Chelated Copper/acre foot or 0.1 to 0.5 ppm elemental copper.
Fluridone 0.25 to 0.5 gal/surface acre. Check with Company rep for exact rates.
Glyphosate 4 to 7.5 pt/surface acre of 5.4L.
Triclopyr 2 to 8 quarts per surface acre of 3L
Sodium Carbonate Peroxyhydrate 3 to 170 pounds per acre-foot of 50G
Imazypyr 1 pint to 6 pints per surface acre of 2 lb. per gallon. Aquatic Pesticide Applicator License required
*Acre foot = 1 surface acre of water (43,560 ft 2) 1 foot deep.

Rates vary with weed species, water quality, percent active ingredient of formulated product and specific company label. Follow the label exactly.

Effectiveness of Herbicides for Aquatic Weed Control
(printer-friendly format)

Weed Copper complexes, copper sulfate (various) 2,4-D (various) Diquat (various) Endothall Fluridone (various) Glyphosate (various) Sodium Carbonate Peroxyhydrate Triclopyr Imazapyr
Aquathol K
Aquathol G
Hydrothol G
Hydrothol 191
Filamentous E P P G E
Planktonic E P G G E
Branched (Chara) E P G G
Nitella E P G G
Floating Plants
Bladderwort P P E E
Duckweeds P G1 G P P E P *
Water hyacinth P E E P G * *
Watermeal P P P G P
Submersed Plants
Broadleaf watermilfoil P E E E E P *
Coontail P G E E E E P
Egeria P P G F F E P
Elodea P E F F E P
Eurasian watermilfoil P E E E E E P *
Fanwort P F G E E E P
Hydrilla F2 P G G G E P
Naiads P F E E E E P
Parrotfeather P E E E E F * *
Pondweeds (Potamogeton) P P G E E E P
Emergent Plants
Alders P E F P P P E *
Alligatorweed P F P P P G E * *
American lotus P E P P P F G *
Arrowhead P E G G G E * *
Buttonbush P E F P P P G
Cattails P G G P P F E *
Common reed P P P P P P G *
Fragrant & white waterlily P E P P P E E * *
Frogbit P E E * *
Maidencane P P F F E
Most grasses P P P P P P G *
Pickerelweed P G G P F * *
Pond edge annuals P G E E
Rush P P F P P F E *
Sedges and rushes P F F P P P G
Slender spikerush P G G P
Smartweed P E F F E * *
Spatterdock P E P P P E G-E * *
Southern watergrass P P G E
Torpedograss P P P F G *
Watershield P E P G G
Water pennywort P G G P P P G * *
Water primrose P E F F E * *
Willows P E F P P P E * *
E=excellent control (90 to 100%); G=good control (80 to 89%); F=fair control (70 to 79%); P=poor control (<70%). A blank space indicates weed response is not known.

1Ester formulations only.

2Copper complex only.

*=new herbicides – these plants are listed on the label as being controlled by these herbicides.

Read and follow the label on the herbicide container. Labels change frequently and the label is the law

Waiting Period (Days) Before Using Water After Application of Herbicides for Aquatic Weed Control
(Printer-friendly format)

Common Herbicide Name Trade Name Irrigation Fish Consumption Watering Livestock Swimming
Copper Crystalline copper sulfate and various liquid organic copper complexes NR1 NR NR NR
2,4-D Various formulations and manufacturers2 Water use restrictions vary by formulation and manufacturer. In general, if water is used for irrigating crops, 2,4-D should not be used. Certain labels allow irrigation if an approved chemical assay has reached acceptable levels. A few labels allow irrigation with specific waiting periods.
Diquat Reward 3 to 53 NR 1 NR
Weedtrine D 5 NR 5 NR
Endothall Aquathol K 7 to 25 NR 7 to 25 NR
Aquathol granular 7 NR 7 NR
Aquathol Super K 7 NR 7 NR
Hydrothol 191 7 to 25 NR 7 to 25 NR
Hydrothol 191 granular 7 to 25 NR 7 to 25 NR
Fluridone Avast, Sonar AS, Sonar SRP, Sonar PR, Sonar Q 7-30+ NR NR NR
Glyphosate Rodeo, AquaNeat, Eagre, AquaMaster, AquaPro NR NR NR NR
Sodium Carbonate Peroxyhydrate GreenClean, PAK 27 NR NR NR NR
Triclopyr Renovate 3 1204 NR5 NR
Imazapyr 120
1 NR = No restrictions.

2 Most formulations do not permit application to ponds used for irrigation or for watering dairy cattle.

3 Three days for irrigation of turf and nonfood crops; five days for irrigation of food crops (including tobacco) or for preparation of agricultural sprays.

4 No restriction for established grasses.

5 14 Day restriction on grazing site and growing. Season grazing restriction on lactating livestock after irrigating pasture.

If this document didn’t answer your questions, please contact HGIC at or 1-888-656-9988.

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