Sometimes aquatic weeds like azolla get so out of control, you need to bring in mechanical harvesters to remove the majority of the vegetation before treating the water.
In this situation, we organised mechanical removal of the azolla before spot spraying the small amounts left with herbicide. We then supplied the client with Biostim (to be applied monthly) to help prevent the azolla from returning.
Note: If you were to just spray the azolla with herbicide, the vegetation would die and settle on the bottom, degrading and becoming fertiliser for future blooms. Meaning next season the azolla will likely be back and even more aggressive. Mechanical removal stops the weed becoming fertiliser, and Biostim changes the conditions of the water, starving the water of nutrients, which tackles the cause of the azolla; preventing future blooms.