Dear Erik: I have a problem. I recently put together a system based upon your article on aero-hydroponics. I started with hydroponics and am now converting to rockwool as a medium. The system works just fine. I’m using a medium strength full-spectrum hydroponics mix and watching the pH carefully with a well-calibrated quality meter. In spite of this, plants (very similar to hops) are dying. That is why your article on fungus gnats caught my eye.
Yes, I have seen those bugs hanging around the plants. I’m positive they are fungus gnats. I talked to my hydroponic store and they told me they took the product for this problem, Wilson’s, off the shelf because people were complaining that it was ineffective for this problem. The store owner recommended another brand and I treated them with this. I also treated them with a fungicide. What else can I do?
From Erik: It sounds like you have identified the pest. Fungus gnat adults can easily be seen buzzing around. It’s their larval offspring in the rockwool that are the most detrimental. They feed on plant roots and transmit pathogens such as fungal infections and viruses. However, this might not be the cause of your plant’s ill fate. The plants might me suffering from a nutritional disorder caused by an infection or other conditions such as high TDS levels in the root zone, as fertilizer build up can occur in the rockwool. Toxicicity from over application of pesticides at the roots is a consideration.
Start with fresh plants and media after thoroughly cleaning and fumigating the grow area and all of the equipment. Inline U.V. sterilizers for the irrigation system can be helpful but are not perfect. Erik B.