Aquatic Herbicides - Pond Weed Killer

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Cattail Killer Pack to kill cattails

How to get rid of Pond Weeds Safely

Some pond weeds, like cattails and phragmites, are very difficult aquatic plants to remove after they have established.

A wide variety of pond weeds can show up in a pond. Often, the plants initially provide welcome structure and fish habitat in the pond. Native aquatic plants usually grow at a moderate rate and don't take over a pond. (There are some exceptions).

Invasive aquatic plants are typically just the opposite - aggressive spreaders that overtake ponds, limit sunlight for native plants, and consume dissolved oxygen during critical nighttime hours.

Cattails spread in two ways by their fluffy airborne seeds and from extensive root systems. Particularly in shallow ponds and wetlands, cattails can outcompete many other beneficial pond plants and create a monoculture.

Digging the cattail plants out can be difficult at best and almost always leaves root fragments behind that begin to grow new plants. The best way to remove cattails from a pond is actually a 2-part process. First, remove as many plants and roots as possible. Then follow up with a chemical treatment using an aquatic glyphosphate paired with a water-safe surfactant to help the chemical penetrate the plant leaves.

Phragmites, commonly seen in wetland pond margins and roadside ditches is an extremely tall (over 8 feet) reed grass that shades everything below effectively eliminating competition. Phragmites plants are also spread by seeds and rhizome root systems.

In much the same way as the shoreline weeds, floating and submerged weeds can also spread aggressively and damage the pond ecosystem.

Pond Weed Control for Emergent Weeds

Emergent weeds like cattail, bulrush, phragmites, purple loosestrife, alligator weed, some iris, and sedges are challenging to control because of their extensive root systems. Since the plants have so many roots, physical removal alone is not an effective treatment. However, they are readily controlled with basic aquatic herbicides.

Emergent weeds have their roots and at times, part of the leaves submerged in the water. As the name suggests, the plants grow up and out of the water along pond and lake shores.

Best Emergent Pond Weed Killer - Aquatic herbicides for Emergent Pond Weed

Because of the extensive root systems found in many emergent pond weeds, treatment with a water-safe herbicide is usually the most effective way to control the weeds. When used according to the product label, aquatic herbicides are safe for fish and other aquatic organisms.

It is important to use a systematic herbicide that is drawn to the root of the weed killing the entire plant. The best time of year to treat cattails and other root spread pond weeds is late in the growing season when the plants are actively drawing nutrients from the leaves toward the roots. Chemical application during this time results in the herbicide being drawn more quickly to the roots.

As with all aquatic herbicides, treating early in the morning on a sunny day is most effective to kill pond weeds.

Glyphosphate based herbicides like Cattplex combined with a treatment enhancer aka surfactant (Plexmate) are the best weed killer for the emergent plants.

Floating Aquatic Weed Killer

Common floating weeds include watermeal, duckweed, water lettuce, hyacinth, spatterdock, watershield and water lily. Some of the floating pond weeds (watermeal, duckweed, water lettuce, and hyacinth) do not attach to the pond bottom and can be found anywhere (sometimes everywhere) in a pond or lake. Water lily, Watershield, and Spatterdock have roots, but the leaves and flowers float on the surface.

Best Floating Weed Control Methods:

Manual Removal

In small amounts, floating weeds such as water lettuce or hyacinth that grow on the surface can be raked or skimmed from the pond. 

Water Movement

The smallest floating aquatic weeds can be managed by creating disturbance on the pond surface with either a diffused air aeration system or floating pond fountain. The water movement on the pond makes it more difficult for the plants to stay afloat and reproduce.

Aquatic Herbicides for Floating Weeds

For the free-floating type of weeds, a contact herbicide or combination of herbicides like the Duckweed Destroyer Pack is the best choice.

Plants with roots and leaves that float all the way to the surface are best treated with Cattplex and Plexmate. The Plexmate surfactant helps the aquatic herbicide to penetrate the often waxy floating leaves.

Submerged Weed Treatments

Underwater weeds cause a number of issues in pond including depleting precious oxygen at night not to mention snagging fishing lures. Problem plants include Cabomba (Fanwort), sago pondweed, coontail, American Pondweed species, Parrot Feather, Bladderwort, Hydrilla, Southern Naiad, and Eurasian water milfoil.

Best Submerged Weed Control

Physical removal of submerged pond weeds requires sophisticated equipment and often results in a temporary improvement with the weeds returning quickly.

Pond Dye

Using pond dye to shade the pond can slow the growth of many underwater weeds. Aquatic plants need sunlight for photosynthesis and growth so blocking sunlight will reduce the amount of growth. Don't be afraid to use extra doses of pond dye to limit sunlight.

Submerged Pond Weed Herbicides

There are a wide variety of herbicides available to treat underwater plants. In many cases, the best weed killer depends on the exact species of aquatic weed being treated. Some granular weed killers provide full-season treatment. Other contact herbicides such as a diquat herbicide are fast-acting, but do not give long-term protection.

We recommend consulting our pond weed identification guide that has treatment recommendations for the most common submerged aquatic weeds.