How to control both Duckweed & Salvinia together in a small dam
Q. We are battling infestations of duckweed AND salvinia and need advice on what products to use. We are also interested in Muck Breaker. We have a hopeful vision of wanting to completely irradicate duckweed and salvinia from our dam.
ANSWER
If you’re dealing with duckweed and salvinia taking over a relatively small dam, you’re not alone — and the good news is that these issues are manageable with the right approach.
Even in a dam of around 500 sqm, floating weeds can quickly get out of hand if conditions are right. Here’s how to tackle the problem effectively, both in the short term and for long-term water health.
Step 1: Consider a Water Test
Before making ongoing changes, a water test is a great starting point. It helps identify nutrient levels and underlying imbalances that may be fuelling weed growth. Understanding what’s happening beneath the surface allows for more targeted and effective treatment.
Step 2: Getting the Most Out of AQ200 + Wetter
AQ200 combined with Wetter is an effective treatment for duckweed and salvinia — but application method is critical.
If you haven’t seen results so far, the issue is often how the product is applied rather than the product itself.
Key application tips:
Follow the safety & usage guidelines
Note requires withholding the use of water for 10 days after treatment
Use a shower spray, not a fine mist
Apply a single, heavy coating to thoroughly wet the plants
Avoid light or patchy spraying
Salvinia often grows in dense, multi-layered mats. To be effective, the spray must penetrate through the layers — this means applying a very thick coating.
If the treated plants aren’t sinking, this can be due to shallow water or tightly packed coverage. In these cases, adding Surface Clear can assist with the sinking process and improve results.
Once treatment begins, continue weekly spot spraying until all salvinia is eliminated. Even a tiny leftover fragment can quickly regrow into a full bloom.
Step 3: Long-Term Water Quality Solutions
Once floating weeds are under control, improving overall water quality will help prevent them from returning. There are two proven options — and they can be used individually or together.
1. Aeration
If power is available nearby, aeration is one of the most effective long-term solutions. A ½ HP aeration fountain improves oxygen levels, circulation, and overall water balance, making conditions far less favourable for problem weeds.
2. Bacterial Treatment
A bacterial treatment such as Muck Breaker helps break down organic matter that settles on the bottom after weed die-off.
Start with 5 pucks every two weeks
Continue until water quality improves
Reduce the application rate once conditions stabilise
This process reduces nutrient buildup and helps prevent future outbreaks.
Helpful Resources
For more detailed guidance, these resources are worth a look:
Salvinia Treatment Manual
Duckweed Treatment Manual
Quick Salvinia Treatment Guide
Quick Duckweed Treatment Guide
Final Thoughts
Duckweed and salvinia can be persistent, but with correct application, follow-up spraying, and long-term water management, even heavily affected dams can be brought back into balance.
If you’re unsure where to start, a water test and a solid treatment plan can make all the difference — and save time and money in the long run.
