What is the best way to control primary mold?

I am not entirely sure what you are referring to as primary mold but I do know how to battle molds, mildews and fungi. The best solution, in my opinion, is sulfur. Sulfur kills molds and mildews on contact. Sulfur can be bought in powdered form that can be dusted on the plant leaves. I like to use a soft brush and dust the leaves gently, as if I am a detective dusting for prints. This is most effective if you only have a few plants.

For getting rid of mold on a large scale I recommend using a sulfur burner. A sulfur burner will vaporize sulfur pellets, filling your room with a sulfur mist. When doing this make sure your ventilation is off for 10 minutes or so. Also make sure there are no exposed flames such as a pilot light, because it can ignite the sulfur mist.

There are other methods that are less effective but will do the trick. You can spray the plants with a diluted ammonia/water solution at one part ammonia to 20 parts water. This is effective and relatively safe. Neem tree oil sprays and pine tree oil sprays can also help eliminate mold. There are also a wide range of copper-based fungicides available. They are highly effective but only practical on a small scale.

To help prevent a recurring mold problem try to lower humidity levels and temperature in your growroom. Also keep your growroom immaculately clean, ensuring to wash equipment in between crops.

All of these solutions should be available at any quality hydroponic retailer, and the staff should be able to walk you through whichever choice you make. I hope this helps.

–Erik Biksa