Duckweed and Watermeal are free floating pond weeds that are found in wetlands and nutrient rich stagnant water. They are often mistaken for algae. Pond weed identification can be done by recognizing its small, round floating “frond” or leaf. Duckweed frond has hanging roots and is roughly the diameter of a pencil eraser. Watermeal has no roots and looks like floating grass seed about the size of a pin-head. Duckweed and Watermeal reproduce by budding on the margin or base of the frond. Each frond can only do this a limited number of times before dying. Both survive freezing and drought by producing seeds or buds “turion” that sink to the bottom after being released from mother frond. Both are most commonly transported by waterfowl.
Duckweed and Watermeal do serve as food for waterfowl and fish. They multiply incredibly fast when conditions are right. Both block sunlight and absorb nutrients (phosphorus & nitrogen) from the pond thus out compete algae. By absorbing nutrients, they act as a natural water purifier by removing unwanted matter by as much as 99 percent. Both also block sunlight which can reduce water loss from evaporation by as much as 33 percent.
Overabundance of Duckweed and Watermeal indicate excessive nutrients exist in the water. These nutrients may often come from runoff. Heavy infestation will inhibit oxygen exchange and reduce dissolved oxygen when weeds die and decay. This can kill fish and clog outlets such as water drains.
Physical control is accomplished by netting or raking off the water surface. Vacuum devices can also be used to skim these pond weeds from small ponds. Aerators also disrupt surface water which may limit growth.
Chemical control is accomplished with fluridone (Sonar A.S. Liquid) or diquat dibromide (Weedtrine-D Liquid). Chemical intervention won’t solve the problem of excessive nutrients in water. Ponds with high nutrient level may require chemical treatment every spring to maintain control.
• Reducing fertilizer applications near the pond.
• Maintain septic system.
• Redirect nutrient-rich runoff away from pond.
• Maintain vegetative buffer strips around pond.
• Apply beneficial bacteria for pond muck removal and reduce nutrient level.
For further information visit: www.sfr.cas.psu.edu/water
Please feel free to email me or post questions you may have and I will respond accordingly.