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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

Controlling Duckweed & Watermeal – Pond & Lake Q & A

Q: I think I have duckweed and watermeal. It’s taking over my pond! I can’t seem to get ahead of it! What do I do?
- Several Customers

Picture of DuckweedA: Duckweed and watermeal are very prolific growers and can cover a pond before you know it. When covering a pond it can look like algae, but up close you can see it’s not (see pictures on the left). You can try to rake the duckweed and watermeal off the pond’s surface but more will be back within the week. The absolute best way to get rid of duckweed is to use a product called Sonar™ A.S.. The best way to get rid of watermeal is to use a product called Clipper™. Sonar™ A.S. works by inhibiting the weed’s ability to produce carotene. Without this ability, chlorophyll is rapidly degraded by sunlight and the weeds die. The only water use restriction is a 30 day irrigation restriction.

Both Sonar™ A.S. and Clipper™ will also get rid of many other submerged weeds in the pond and will produce season-long results in as little as 30-45 days.

Picture of WatermealFor more information on these herbicides and the aquatic weeds they will control, click here.

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