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.
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.
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?