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I think I have either milfoil or coontail. How do I tell the difference, and what chemical should I use? | Ponds & Lakes Q&A

Q: I think I have either milfoil or coontail. How do I tell the difference, and what chemical should I use?

Q: I think I have either milfoil or coontail. How do I tell the difference, and what chemical should I use?

Paul – Greenfield, OH

A: Invasive aquatic plants like milfoil and coontail can cause trouble in your pond or lake. Though they provide food and shelter for birds, insects, fish and other pond critters, they can form dense colonies, reducing access to open water, limiting fishing access, and interfering with boating and swimming.

Milfoil and coontail look similar and – thankfully – can be treated with similar chemicals. Here’s what you need to know about identifying and managing these nuisance plants.

Milfoil Identification

When you think milfoil, think feather-like.

Many different species of milfoil and watermilfoil exist in North America. In general, milfoil is found in water that’s less than 20 feet (6 meters) deep. In water less than 15 feet (4½ meters) deep, it can form dense mats over the surface. The plant is comprised of long stems with air canals and flat, feather-like, whorled leaves that are pinnately divided.

Milfoil is an important food source for waterfowl, but these nuisance plants can aggressively invade lakes, ponds and waterways. Once they’re established, they’re almost impossible to eradicate, and so periodic maintenance is necessary to keep them under control.

Coontail Identification

When coontail comes to mind, think of a Christmas tree.

Also known as hornwort, coontail also thrives in water less than 20 feet deep. The rootless invasive plant grows below the surface, and it has a central hollow stem and dark green leaves that are spiny, forked and bushy near the tip, giving it its “coontail” or Christmas tree appearance.

Like milfoil, coontail provides food for waterfowl and cover for young bluegills, perch, largemouth bass and northern pike, but it needs to be managed to prevent it from taking over your pond or lake.

Keeping Them Under Control

Many of the submerged weed chemicals available treat both milfoil and coontail. Depending how you use your pond, the best choices are:

  • Ultra PondWeed Defense®: This liquid herbicide has short-term drinking (three days for human consumption; one day for animal consumption) and irrigation restrictions (five days).
  • Navigate: A granular herbicide, Navigate is great for spot-treating problem areas. It has longer consumption and irrigation restrictions (21 days) than the others.
  • Fluridone (Sonar™): If your entire pond is infested, try Sonar™. It can kill the invaders down to their roots, but expect slower results (it can take up to 90 days for full protection) and longer irrigation restrictions (30 days). Note: Sonar™ should only be used in ponds with little to no flow.
  • Clipper™: To use Clipper™, you’ll need to mix the quick-dissolve granules with water – but you can start using the water again for irrigation in just five days.

Regardless which one you choose, the best time to apply it is when the weeds are actively growing.

Help from the Experts

If you can’t figure out which aquatic weed is growing in your pond, pull one (or more!) from the pond, snap a picture and email it, or mail us a sample in a dry paper towel. We can help you identify the invader and suggest the best chemical to control it.

Pond Talk: What’s your go-to herbicide to treat invasive aquatic plants?

Broad Spectrum Pondweed Control - Pond Logic® Ultra PondWeed Defense®


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I think I have duckweed or watermeal. How do I know? And how do I treat it? | Ponds & Lakes Q&A

Q: I think I have duckweed or watermeal. How do I know? And how do I treat it?

Q: I think I have duckweed or watermeal. How do I know? And how do I treat it?

Richard – Fishers, IN

A: Duckweed and watermeal are both pond pests. Dense colonies of these prolific plants can completely cover the surface of a lake or fish pond, causing dissolved oxygen depletions and fish kills. These tiny invaders need to be managed before they take over.

But before you control them, you need to get to know them. Let’s meet these troublemakers.


The smallest seed-bearing plants in the world, watermeal is a very tiny (less than 1 millimeter) light green free-floating rootless plant that resembles green cornmeal. They prefer quiet water that’s undisturbed by waves, and they’re often associated with colonies of duckweed and mosquito fern (azzola). Unchecked, these plants can be aggressive invaders.


Duckweed is another very small light green free-floating plant, but unlike watermeal, duckweed has a single root and one to three leaves, or fronds, that measure 1/16- to 1/8-inch long. Like watermeal, duckweed tends to grow in dense colonies in quiet water that’s undisturbed by wave action. Duckweed colonies provide habitat for micro invertebrates, but if it completely covers the surface of a pond for an extended period, it will cause oxygen depletions. As its name implies, duckweed is often gobbled by ducks, which also transport it to other bodies of water but you cannot count them for keeping the weed in control.

Stop the Invasion!

To control these aquatic bad guys, you’ll need a herbicide. Clipper™ and Ultra PondWeed Defense® are both selective plant killers that will attack watermeal and duckweed. They’re a short-term solution for both—be sure to apply as directed.

For long-term control of duckweed, you’ll need something a bit stronger. We recommend Sonar™ A.S.. It’s formulated to control stubborn aquatic weeds all season long. Don’t forget to add pond dye, it protects the Sonar™ A.S. from being quickly degraded by the sun.

Pond Talk: Tell us about your experiences with duckweed and watermeal. Do you have any additional management tips to share?

Deliver Fast & Selective Control Of Weeds - Valent® Clipper™ Aquatic Herbicide

Controlling Pondweeds: Duckweed – Pond & Lake Q & A – Week Ending March 28th

Picture of Duckweed Floating in a Pond.

Pond & Lake Q & A

Q: Last year I had an uncontrollable case of duckweed in my pond. It covered my entire 1/2 acre pond! I’ve heard of your product called WhiteCap and wanted to use it this spring. I don’t see any signs of duckweed yet, but was wondering if it is too early to treat.
– Cameron of Michigan

A: Duckweed can take over a pond. This prolific grower can come from many sources although most commonly brought in on the feet of waterfowl such as ducks, geese or even herons. The small plant can stick to the feet or the feathers of such birds and be carried for miles. Duckweed can start out slow and in some cases take several seasons to become a problem, although I would recommend treating for it as early as possible.

There are a few options when treating duckweed. You can use a fast-acting aquatic herbicide such as Ultra PondWeed Defense® although this will only give you temporary relief and require multiple applications of spraying the duckweed directly. These are not usually suggested unless your treatment areas are not contained or you have heavy water turnover. When possible I always suggest Sonar™ A.S. since it is the least expensive method of treating an entire pond, is easy to apply and lasts an entire season.

We recommend to use 32 oz or 1 quart per surface acre (4-6′ deep) when treating for duckweed. This means Cameron’s 1/2 acre pond can be treated with just 16 oz of Sonar™ A.S.!

To answer the question above, treat with Sonar™ A.S. in the early spring before the duckweed even appears. This will allow you to get ahead of it before it reaches the surface. Although you don’t generally see it Duckweed is actually growing at the bottom of your pond long before you see it at the surface.

There are also other nice benefits to Sonar™ A.S. such as: It works very slowly so there is no chance of oxygen loss that could harm your fish or other aquatic life. Sonar™ A.S. is also very effective at controlling most other nuisance aquatic plants. So when your treat for your duckweed you will be controlling most other species as well.

Please Note: Sonar™ A.S. needs to stay in your pond for up to 90 days. It is not recommended to use it in ponds with a heavy overflow or when during times of heavy rain. If you are unsure of your pond’s turnover (or amount of water that is exchanged) use Nature’s Blue™ Pond Dye to shade the water column and track the time it takes for the color to disappear. You may also use Nature’s Blue™ Pond Dye during a Sonar™ A.S. treatment to track turnover and shade the pond from sunlight which can also reduce the life span of Sonar™ A.S.