Watermeal | Identify and Control

Overview

Watermeal, or Wolffia Columbiana, is a tiny rootless floating plant that can sometimes be confused with duckweed. Watermeal looks like tiny little balls while duckweed looks like small clovers floating on the water. These plants can cover an entire pond if not properly controlled. Watermeal weed control will also kill duckweed. Aeration can help prevent plant growth by keeping the water moving.

What Does Watermeal Look Like?

Watermeal is a very small plant that’s size compares to strawberry seeds or corn meal up close. Each plant grows to about the size of a pencil tip, measuring up to fifty-nine thousandths of an inch long. The plants can be round or oblong, and the color can range from light to bright green.

Flowers develop on watermeal plants but can only be seen through a microscope. These plants reproduce from seeds that drop to the bottom of the water when it’s too cold; when the conditions are right in the spring, watermeal seeds rise to the surface to sprout. Another identifiable trait of watermeal in ponds is that it can make swirls on top of the water and will sometimes look like a uniform mat from afar.

Watermeal thrives in still or slow-moving bodies of water and is most common in ponds. This plant can be found across the United States which makes it a frequent problem for pond owners. It can double its mass in just days, posing not only an eyesore but possible oxygen depletion. An infestation of watermeal can block out the sunlight needed for photosynthesis, which can cause fish kills.

Watermeal vs. Duckweed

Watermeal and duckweed can get mistaken for each other, but it is more common to confuse watermeal for duckweed since duckweed is the most well-known of the two. Both plants float on top of the water, but a notable difference is that duckweed has three leaves and roots with three to eleven nerves that extend into the water while watermeal has no roots and is round.

Mature duckweed leaves look like small clovers with two to five fronds. The leaves on duckweed are round or egg shaped and have roots that hang from them. Duckweed leaves are larger than watermeal plants, about one-sixteenth to one-eighth of an inch long once fully developed.

While duckweed is small, watermeal is even smaller. Watermeal is comparable to corn meal in size and texture and has no roots. Each plant will grow to be thirty-nine thousandths of an inch to fifty-nine thousandths of an inch once fully developed, which is around the size of a pinhead.

It is typical for watermeal and duckweed to get confused for each other. They are both green in color, replicate quickly, and can cover an entire pond’s surface in a matter of days. What kills watermeal will control both weeds; some herbicides for duckweed will harm watermeal but not completely control it. Duckweed and watermeal are commonly found together on the tops of ponds so a hybrid treatment is often necessary.

Watermeal Control

The best herbicide for watermeal in a pond is flumioxazin. There are multiple brand names of this herbicide, including Flumigard and Semera. The active ingredient in these herbicides is the same. These products come in liquid or granules, but either one needs to be mixed with a surfactant and water then sprayed over the surface. Because these plants are so small and reproduce quickly, spraying every piece is necessary for controlling watermeal on ponds.

will effectively kill watermeal as well as duckweed when present. Both plants can turn white when stressed or dying. In most cases flumioxazin should produce sufficient results one to two weeks after using the product. In more severe cases, such as when there is a thick mat covering the pond, multiple treatments may be necessary.

An aerator or fountain can help watermeal control in ponds.  The moving water deters growth since watermeal grows best in stagnant bodies of water. Fountains also add a beautiful centerpiece to ponds and provide a source of relaxing sights and sounds.

Conclusion

Tiny, round or oblong bright green watermeal plants can grow quickly and easily take over a whole pond in a matter of days. The swirling on the surface is a sign that it’s time for action. Whether watermeal is present alone or is combined with duckweed, control can be obtained by using a flumioxazin herbicide, Flumigard or Semera.