Watermeal Control Guide

Watermeal is identified by its very small, oval single leaf that has no roots. It has the appearance of floating grass seed on the surface of the pond and is typically found along with Duckweed. The leaf of Watermeal ranges from 0.2 to 1.5 millimeters in length, about the size of a pin-head and much smaller than Duckweed. Watermeal and Duckweed are the smallest aquatic plants known. Watermeal reproduces by budding and fragmentation, it can be an aggressive invader making ponds unsightly and unusable. These tiny plants can be more than an eyesore; heavy amounts of growth can prevent sunlight from reaching deeper parts of the pond, preventing underwater plants from photosynthesizing and producing oxygen. In turn, that lack of oxygen can stress or kill fish.


These plants require a lot of nutrients to grow, so typically they are found in nutrient rich environments such as ponds that receive drainage from farm fields, feed lots, septic systems, lawns, and golf courses. The bottom sediments of infested ponds are often very mucky and nutrient rich. To prevent its overabundance it is necessary to reduce fertilizer application near the pond, maintain septic systems properly, redirect nutrient-rich runoff away for the pond and maintain a vegetative buffer strip around your pond. If the excess of nutrients are not addressed, plant overgrowth will always be present and it will need to be constantly managed.

Watermeal can be spread from one pond to another by humans and wildlife. The small plants stick to the sides of boats, or lodge in the feathers of birds swimming in infested waters. When the boat enters a new body of water or the birds migrate, the plants go with them.

Biological Control

Beneficial Bacteria Products enzymes such as PZ-900 feed on nutrients in the water making them unavailable for plant growth. Reducing nutrients can help prevent invasion.

Physical/Mechanical Control

Physical control of duckweed is usually accomplished by netting or raking the plants off the pond and then disposing of plant material away from the pond so that the wind or runoff cannot transport it back into the water. Physical removal along with chemical control and a reduction of nutrients entering the pond will maximize success.

Surface Aeration has also been used as a mechanical approach to hinder duckweed proliferation. Duckweed prefers to grow in stagnant water, aerators will disrupt the surface of the water and limit the growth of these plants to the sides of the pond where they can easily be removed using nets or a rake. Furthermore, the added oxygen will accelerate the decomposition process of nutrients that feed pondweeds and algae during the summer months.

Chemical Control

Sonar AS & Sonar RTURewardWeedtrine-D and Clipper have been proven successful in treating Duckweed.  A nonionic surfactant such as Cygnet Plus should be mixed in solution with specific herbicides when plants are treated. 

* Sonar AS & Sonar RTU are ready-to-use products and do not require a surfactant such as Cygnet Plus for proper application. 

Sonar AS is long lasting systemic herbicide ideal for water bodies with minimal flow or discharge. Simply mix Sonar A.S. with water and pour in different spots around the pond. 

Sonar RTU (Ready-To-Use) is a long lasting, systemic, easy to use herbicide. Sonar RTU does not require mixing, it can be applied directly from the bottle by simply pouring into multiple locations around the water body. 

Clipper is a broad spectrum, fast acting, contact algaecide & herbicide. It comes in a water soluble granule that mixes with water to be sprayed directly onto the target plant. Clipper should be applied to actively growing plants or algal blooms.

Reward and Weedtrine-D are both broad spectrum, rapid-acting, contact herbicides ideal for use on small bodies of water or small weed patches. Successfully control a broad range of submersed, floating and emergent weeds in lakes, ponds, and drainage ditches. Rapidly absorbed by foliage, Reward and Weedtrine-D herbicide begin to work immediately on contact. 

Cygnet Plus is a nonionic wetting agent, sticker, activator and penetrant all in one. Cygnet Plus Increases the effectiveness of herbicides uptake into the plant tissue.