Fungus Gnats

[Cher Kilgore]

I hope I'm posting this in the right place. 

 

I am constantly loosing the battle against fungus gnats. It's not the adults that are the problem but the larva. Everytime I think I have an answer they come back and go nuts. This time they have been destroying all my Onions from the inside of the bulb out.

 

We have a constant flood and drain system. Basically the water is always coming in and going out. 

We've tried Nematoads, BT Thuriside, Mosquito dunks,  Alchoal spray, washing all the rock out and starting over, placing cut potatoes on the rock and even flooding the system and sweeping all of the larva out. I have sticky traps every where and still can't get them controled. 

 

Please any ideas or suggestions? Our system is inside our house in an extra room, so there are certain things we can't use. And we can only afford low cost solutions. I'm willing to try anything! Our plants were looking great but the Tomato leaves are starting to be affected.

 

Thank you so much for any info!!

[Rob Nash]

come to think of it, the hydro shop does sell it out of a bucket, in zip lock bags.. that they must have filled. with just a printed label and price.

I like the idea of the dunks. if they are harmless to fish, it sure would be convenient if we could just set them under the inlet water, or in a raft and let them do their thing.   ..now I understand why dunks are so pricey.

we really haven't had any outbreaks this year ..the only place I ever see gnats anymore, is the coir in the seedling trays or in the net pots in the rafts. ..how cool would be if all you needed was a dunk in one of the raft's holes.

to use the gnatrol, I mix it into a gallon of water and dunk the roots, net pot, coir and all when transplanting into the rafts.

...this can add up to be quite a chore, but does knock them out ...but only after about 6 weeks of transplants.

[Mike Coen]

Thanks all for your great concern and time to advise from your experience.  For now, I have beaten the gnats into submission but it only takes two to start a new generation and I doubt I have them 100 percent annihilated.  In the process, I have new media, clean from the dirt that was in my first growbed media which was "washed" pea gravel.  I am using lava rock, more meticulously washed by screen and hose, topped with expanded clay/ceramic pebbles.  I cleaned out half the gravel in the growbeds and then flooded/drained them until I had effectively drowned millions of little larvae of at least two different sizes.  Washed out all dirt but didn't clean surfaces entirely to give the system a head start on bacteria culture.  The process was complicated in that I had to also keep 50 Tilapia happy in a 55 gallon drum with aeration and a heater while the system was refilling and reheating.  Thanks sincerely, Mike

[Kenji Snow]

I have always used BT bacillus thuringiensis israelensis with great success in a commercial greenhouse as a foliar spray and directly into the media beds. I also add it to every brew of compost tea and no gnats or flies. BT (i) is the active ingredient in mosquito dunks but I think concentrated BT (i) has a lot more organisms than the dunks. Also try lowering your water level in the media. I lowered mine 1/2" and it made a difference. They also like plugs if you use them so spray those as well. Yellow sticky traps would also do well in your situation. The key is to break the life cycle of the gnat (or any other pest insect) the fungus gnat lives about 28 days 7 of them are as an adult fly so go for the adults with the sticky traps, hit their offspring with BT (i) and take away their comfortable environment. Organocide is also a great spray you can get at home depot. Its organic and kills a huge array of pests including fungus gnat eggs, larvae and adults.One word of caution...Organocide has fish emulsion in it your plants will love it but you will have a fishy smell for a couple days. .

 

[Kenji Snow]

I have always used BT bacillus thuringiensis israelensis with great success in a commercial greenhouse as a foliar spray and directly into the media beds. I also add it to every brew of compost tea and no gnats or flies. BT (i) is the active ingredient in mosquito dunks but I think concentrated BT (i) has a lot more organisms than the dunks. Also try lowering your water level in the media. I lowered mine 1/2" and it made a difference. They also like plugs if you use them so spray those as well. Yellow sticky traps would also do well in your situation. The key is to break the life cycle of the gnat (or any other pest insect) the fungus gnat lives about 28 days 7 of them are as an adult fly so go for the adults with the sticky traps, hit their offspring with BT (i) and take away their comfortable environment. Organocide is also a great spray you can get at home depot. Its organic and kills a huge array of pests including fungus gnat eggs, larvae and adults.One word of caution...Organocide has fish emulsion in it your plants will love it but you will have a fishy smell for a couple days. .

 

[TCLynx]

Organocide is organic but it is also mostly oil based so I would advise extreme caution about using it anywhere near aquaponics.  Oils can suffocate fish if there is too much that gets in the water.

I think the BT concentrate is a good idea against he fungus gnats and dipping the seedlings or at least their trays in it while tedious, is probably a very effective control for the larva stage.