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I had a bad duckweed problem last year. How do I prevent it this year? | Ponds & Lakes Q&A

Q: I had a bad duckweed problem last year. How do I prevent it this year?

Q: I had a bad duckweed problem last year. How do I prevent it this year?

Alex – Alvada,OH

A: As you know, Duckweed is a persistent pond pest. 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.

ID Duckweed

Transported by waterfowl, Duckweed is a very small, light green, free-floating plant that sports a single hair-like root and three 1/16- to 1/8-inch long leaves, or fronds, that resemble a four-leaf clover. It tends to grow in dense colonies in quiet water that’s undisturbed by waves, and it’s often mistaken for algae.

Though Duckweed colonies can provide a habitat for microscopic critters and forage for hungry ducks, the plant can wipe out oxygen in the water if it grows to cover a lake’s or pond’s surface. That could compromise your fishes’ health and cut off sunlight to underwater plants.

Plant Pest Control

Because Duckweed is such a small plant that spreads very quickly, it can be difficult to control – and so it’s critical to treat your pond or lake early in the spring when the growth first appears.

To manage these aquatic bad guys, you’ll need an herbicide. We recommend Sonar A.S., a weed killer that provides season-long control against unwanted plants like Duckweed. It’s designed for water bodies that have no water outflow, as it can take 30 to 60 days to control established weed growth and up to 90 days for full protection of your pond.

Sonar A.S. degrades quickly in sunlight, and so you must add Pond Dye at the time of treatment. The dye will shade the water and allow the herbicide to work effectively.

Short-Term Solution

If you want to remove the Duckweed for a short period of time but your pond or lake has an outflow that prevents you from using Sonar A.S., you can remove the tiny plants with the Pond Skim. The floating tool, which is 5 feet wide, collects surface debris when dragged across the water.

Pond Talk: How do you remove duckweed from your farm pond or lake?

One Treatment for the Entire Season - Sonar™ Fluridone Aquatic Herbicide

There is an Oil Slick Film Covering My Pond. How Do I Get Rid of It? – Pond & Lake Q & A

Algae, Duckweed, Watermeal & Pollen Identification

Q: There is a brown rust-like film/oil slick covering my pond. Do you have an idea what this might be and how to get rid of it? - Several Customers

A: There are several things this could be: Algae, duckweed, watermeal or pollen.

Determining if Algae is a Problem: Filamentous Algae will float around the pond’s edges in mats while Planktonic Algae will make the whole body of water to look like a “pea soup” green color. If this is the case, using Algae Defense® Algaecide will provide quick control. Follow up with PondClear™ for long-term clear water.

Determining if Duckweed or Watermeal is the Problem: Duckweed and Watermeal are very rapid growers and will cover an entire pond if they get out of control. Looking to the pictures to the left, you can see that Duckweed is a small plant the size of a pencil eraser, while Watermeal is about the size of the tip of a pencil. If you determine that you have Duckweed or Watermeal. Your only long-term option is Sonar™ A.S. for Duckweed and Clipper™ for Watermeal. If you only require short-term control (3-4 weeks) for an event or party Ultra PondWeed Defense®” may be used.

Determining if Pollen is the Problem: What may look like a greenish, brownish algae, may actually be pollen. Pollen may even cause an oil-slick or film on the surface of the pond. There is no magic product that will give you a quick fix. Many times a heavy rain will settle it to the bottom. In many cases if your pond receives good circulation from an aerator or fountain you will not see pollen becoming much of a problem.

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