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?