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Pond Weed Control Options

Types of water weeds

Before choosing a weed killer for ponds, first identify your target weeds. Do they fall into the category of emergent weeds, submerged weeds, or floating weeds. Identify you pond weeds here.

Emergent weeds:

Plant roots are in water or moist soil but the majority of the plant is above water. Examples include cattails, creeping water primrose, iris, phragmites

Submerged weeds:

Plants that remain underwater. They may be rooted or unrooted. Examples include watermilfoil, hydrilla, elodea, naiad, bladderwort, pondweed species

Floating weeds:

Plants that have leaves that float at the surface. These can be rooted or unrooted. Examples include water lilies, spatterdock, watershield, water hyacinth, watermeal, duckweed

Aquatic Herbicide Types:

Common aquatic herbicide terminology-

Broad spectrum herbicide:

Non-selective herbicide, will kill mostly any vegetation it comes in contact with.

Systemic herbicide:

A chemical that is absorbed by the plant down to the root system killing it entirely.

Contact herbicide:

An herbicide that only kills the plant it comes in contact with


An additive used in conjunction with an herbicide to improve effectiveness. Surfactants act as a sticking agent. They also break the surface tension of water for the herbicide to travel to the target water weeds.

The Best Aquatic Herbicide for your pond depends on a variety of factors. Speed of treatment, the weed species being targeted and water quality conditions are all factors to consider before purchasing an aquatic herbicide. Common pond weed killer chemicals include diquat, endothall, fluridone, flumioxazin, 2,4-D, Imazamox, etc. Learn more below about how each aquatic herbicide works, how long it takes to kill water weeds, and how the treatment is applied.


Endothall aquatic herbicide is classified as a contact herbicide. It kills aquatic weeds by interfering with both respiration and photosynthesis of the cells.

The chemical is absorbed into the plant in 12-36 hours. It damages plant tissues, causing cellular breakdown within 2-5 days of treatment/exposure. Full breakdown of vegetation occurs at 3-4 weeks.

The chemical half-life of endothall is 5-10 days.

Aquathol K and Aquathol Super K are aquatic herbicides that contain the active ingredient Endothall. Aquathol K is a liquid formulation and Aquathol Super K is granular. Aquathol K is more suitable for larger treatment areas. Aquathol Super K is best suited for smaller areas or spot treatment.

Irrigation and animal water restrictions, duration of which varies depending on concentration/formulation

Pros: Fast acting, Byproduct is consumed by bacteria for further breakdown, Large range of susceptible species, excellent choice for most submerged plants, no restrictions for swimming fishing or irrigation after application



Diquat aquatic herbicide is a fast acting contact herbicide. It kills pond weeds by disrupting the plant’s cell membranes and interfering with cell respiration. This is a non-selective herbicide so it will affect a wide variety of plants. Aquatic plants will die within 1-2 weeks after herbicide treatment.

Diquat is not a good choice for ponds with muddy water. The chemical will bond to clay particles it comes in contact with instead of submerged pond weeds. Once bonded to the sediment it is not biologically available.

Harvester is an aquatic herbicide that contains diquat.

The chemical half-life of diquat is 1-7 days.

Not as effective in muddy ponds as it is “soil loving”, will bond with clay and silt particles in the water

Pros: Fast acting, Highly soluble in water, Large range of susceptible species

Cons: Not meant for use in muddy water, Consumption and irrigation restrictions may apply, does not kill to the roots,


Fluridone aquatic herbicide is a slow acting, selective systemic herbicide. Fluridone stops the plant from making a protective pigment which prevents chlorophyll from breaking down when exposed to the sun. Results in treated plants can be seen between 7-10 days but the plants will die within a 1-2 month period. Slow acting herbicides reduce the risk of oxygen depletion and fish kills from vegetation die-off.

Aquatic herbicides that include the active ingredient fluridone include Sonar RTU, Sonar AS and Sonar One. Sonar RTU and Sonar AS are concentrated liquid formulations. Sonar One is a pelletized formula.

Plant susceptibility varies on species, possible resistance can develop after repeated use

Pros: Spreads rapidly through water, systemic herbicide-kills weeds to the roots, highly effective for hard to kill species, easy application, excellent aquatic herbicide for submerged weeds, low risk of oxygen levels dropping after application- very safe for fish

Cons: Only effective in plants growing at time of treatment,Long treatment period, 30 day Irrigation restriction


Flumioxazin is a broad spectrum contact herbicide. It attacks the weed by disrupting the synthesis of chlorophyll. This impact stops sunlight absorption by the plant. Can control submerged and floating plants along with some filamentous algae

Treated plants respond quickly and will decompose rapidly. Results occur in 3-7 days.

The half-life of flumioxazin in water with pH of 7 is 24 hours.

The half-life of flumioxazin in water with pH above 9 is 15-20 minutes.

Propeller is an aquatic herbicide that contains flumioxazin. Check label rates prior to application as rates vary for different aquatic weed species. Floating weeds and algae require a lower concentration of flumioxazin than submerged weeds.

Pros: Fast acting, Large range of susceptible species, no restrictions for swimming fishing or irrigation after application

Cons: Not as effective in bodies of water with pH higher than 8.5

2, 4-D:

The aquatic herbicide 2,4-D is a systemic herbicide. Granular 2,4-D sink to the bottom where it activates at the base of the plant to infiltrate the root system of aquatic weeds. It is a selective aquatic herbicide that controls water lilies, watershield, spatterdock cow lily, watermilfoil, water stargrass, water chesnut, coontail and bladderwort.

Plants will begin to show effects within a few days. Decomposition of the aquatic weeds will take place over a longer time period.

30 day irrigation restriction depending on the water body being treated

Navigate granular aquatic herbicide contains the active ingredient 2,4-D.

Pros: Relatively fast acting, Spreads through water rapidly, systemic herbicide-kills weeds to the roots, easy granular application

Cons: Irrigation, swimming, and drinking restrictions


Imazamox aquatic herbicide is a systemic herbicide that is used for emergent weeds. Imazamox prevents the production of acetolactate synthase (ALS) which is responsible for catalyzing the first step in the production of crucial amino acids

Susceptible plants will stop growing shortly after treatment but decomposition will occur over a several week span.

Imazamox should only be applied to plants that are actively growing. This can be used during a drain down to prevent plant re-growth of aquatic vegetation.

Clearcast contains the active ingredient imazamox. Check label rates prior to application as rates vary for different aquatic weed species.

24 hour irrigation restriction depending on the body of water that is being treated

Pros: Relatively fast acting, Can be used during multiple stages of growth, systemic herbicide, excellent for long term control, no restrictions for swimming fishing or irrigation after application

Cons: Plants have been known to gain a resistance with constant use, Irrigation restriction apply post treatment