Common duckweed is a tiny plant that floats on the surface. If not managed, it literally can cover the surface, limit a pond’s respiration, and cause a fish kill. During growing season, it spreads fast. Really fast! This unique plant can double itself in approximately 48-hours. Duckweed may have one to three little green leaves, but usually has two about half as big as a pencil eraser. On close inspection, you see tiny white roots extending from leaf joints. It reproduces by seeds. One plant splits to two, two to four, and so on.
Duckweed can migrate to your pond during high water events. It may arrive on waterfowl. Your dog may pickup sprigs while swimming in a neighbor’s pond and transplant it to yours. Eliminating the pesky plant is a challenge. You can wish for heavy rain to flush it out the spillway. A hard freeze may zap it. You can regularly skim coverage from the surface, but expect quick return. During warm months, stock tilapia to graze it. Multiple chemical applications eventually reduce coverage.
Key points to remember about duckweed. Growth is prolific. Most types float, so it moves around. Surface contact herbicides such as glyphosate will take repeated treatments. Eradicating somedoesn’t necessarily mean you get rid of it. Remember, it reproduces every 48-hours. If using herbicides, carefully select the proper label so you don’t damage desired plants. According to the Extension Service, you can treat it with Fluridone. Reward is a liquid diquat and does a good job. While Reward is a contact product, Fluridone is systemic, gets absorbed into the plant, and stops its ability to photosynthesize. Fluridone reacts slowly and must contact plants for longer periods.
We must emphasize, when selecting a herbicide, carefully follow label instructions. Understand consequences of dead, decaying matter in your favorite fishing hole. One call we don’t want to get is a frantic pondmiester reporting oxygen depletion occurred after treatment.