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What chemical should I use to treat water milfoil? | Ponds & Lakes Q&A


What chemical should I use to treat water milfoil?

Q: What chemical should I use to treat water milfoil?

Douglas – Goddard, KS

A: Before we dive into how to treat this aquatic invader, let’s get to know it a little better first.

Water milfoil, also known as Eurasian Water Milfoil (Myriophyllum spicatum), is a submersed aquatic plant that’s native to Europe, Asia and northern Africa. It has feather-like leaves that grow from white, red or brown stems, and some species produce four-petaled pink or reddish flowers that rise a few inches from the water’s surface.

Eurasian water milfoil thrives on fertile, fine-textured, inorganic sediments. An opportunistic species, the plant prefers water bodies that receive nitrogen and phosphorous-laden runoff, like a farm or agricultural pond. Growth explodes when water temperatures rise, which promote multiple periods of flowing and fragmentation (or when pieces of the plant grow roots and develop new plants).

If left unchecked, water milfoil can dominate a pond or lake in no time.

Controlling Growth

The good news is that you can find myriad products to manage this invasive species. The chemical you choose has to do with several factors.

Closed or open system? If your pond is mostly covered with water milfoil, does not have water flowing in and out, and is not used for irrigation, NovaSource™ WhiteCap® SC Aquatic Herbicide will be your best choice. The product uses the active ingredient fluridone, which effectively controls a wide range of floating, submerged and emergent aquatic vegetation including duckweed, hydrilla, bladderwort, naiad, elodea, water lily, coontail, pondweed and water milfoil – giving you more herbicide bang for your buck.

Small area or large? If you’re treating a smaller area of a pond or lake, Pond Logic® PondWeed Defense® Aquatic Herbicide works like a charm. It’s a rapid-acting contact herbicide that drops aquatic weeds below the water surface in four to seven days, though heavy growth may require a second application in 10 to 12 weeks.

Spray or granular? If you prefer granular herbicides to spray ones and have a smaller area to treat, choose Navigate. This granular herbicide is ideal for spot-treating weeds around docks, beach areas and shorelines, killing the roots of both submerged and floating plants, including water milfoil, coontail and water lilies. You’ll see it go to work within 10 days; you’ll see full effects in three to five weeks.

Plant, Human Considerations

When choosing a chemical herbicide, pay special attention to use restrictions. Some of these products have limitations for use in irrigation ponds, swimming holes and other situations until the chemical has adequately broken down in the water.

Also consider the other critters – plants, fish and animals – that live in your pond. Certain products can harm game fish, koi or goldfish, and can kill off prize water lilies and other welcome aquatic plants.

Pond Talk: How do you manage invasive plants in your pond or lake?

WhiteCap Fluridone Aquatic Herbicide - One Treatment Lasts All Season

6 Responses

  1. Is pond defense safe for fish??

    • Hi Sheila – Yes, PondWeed Defense® is safe for fish with some restrictions to its use. PondWeed Defense® is copper based, so do not use in ponds with koi, goldfish or trout unless your carbonate hardness (KH) is above 50ppm. Many ponds and lakes are above this threshold, but we have single test strips available if you are unsure. When treating a pond with any chemical, only treat up to 1/2 of the pond at one time (1/4 or 1/3 if temperatures are hot) and wait 14 days between treatments. This ensures the dissolved oxygen levels in your pond are high enough for your fish.

    • Another problem is my dog and others swim and drink from this water , yes we have trout and bass

  2. What about controlling milfoil in a pond with fish and desirable water lilies?

    • You will want to use a pressurized tank sprayer with an application wand to contact spray the milfoil while trying your best to avoid the lilies. Your weapon of choice in this scenario would be PondWeed Defense.

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