Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Duckweed control problem

My 1acre pond that is aprox 70 years old, is completely covered in duckweed.
I put three 11inch, sterile, grass-carp in about 2 years ago, and they disappeared.
We used to have grass carp, and they died after 8 years. They successfully controlled the duckweed and algae.
We've tried chemicals to no success.
Should I try larger grass carp, or something else?
There are also many large, trashcan lid sized, snapping turtles.

Have you tried a fluoridone based herbicide, such as Whitecap?

Nick, it is a common misconception that Grass Carp (White Amur) will control or even eat Filamentous algae or Duck weed. Duckweed reproduses far too fast and they just won't eat FA unless they are starving and they expend more energy digesting FA than they can extract from it.

Well it's gone from bad to worse, this stuff has not died from the first frost, and it's turned red. It is also much thicker to the tune of 1 1/2 ". This makes it really hard to go down the overflow pipes. Any ideas?

Looks like you have mostly azolla or water fern (red). Hard to tell but maybe some watermeal? Galleon (penoxsulam active ingredient)will control both the duckweed and water fern.

That is thick! I am surprised any fish can even live in there...

If you can figure a way to rake the azolla and watermeal and heap the bulk of it around the shore, in high density, you can trigger a biological reaction where the decaying stuff takes out the live plants.

Regards, andy

Azolla is a very interesting plant. It is a true fern and therefore reproduces by spores and well as Asexual reproduction. A stand of Azolla can double in size in 3-4 days time. But what I find most interesting is that if grows it's own algae inside of it. An algae (actually cyanobacteria) called Anabaena and that's where the plants red color comes from. Anabaena is capable of fixing Nitrogen out of the atmosphere, this is why Azolla relies on it. Phosphorus is the only nutrient that truly limits it's growth, and I bet if you test you water for phosphorus you will find it's high.
Some scientist even believe that Azolla is responsible for life as we know it. Google "Azolla Event" if you are interested.
Azolla is often confused with duckweed but if you look close enough you will see that they are very different.



Anyway though you might like to know a little more about your new pond invader. My first choice for control is Fluridone, and don't skimp on the treatment rate, especially since there is also watermeal. Diquat works well but requires multiple applications and serious commitment to stay on top of it.

In case it hasn't already be noted on the forum, Watermeal is the smallest flowering plant in the world.
And a pic of Anabaena to top it off.