Fungus gnats have invaded my Mom tent. I’m not surprised, because fungus gnats are everywhere but Antarctica, and they proliferate around plants and vegetation. Fruit flies are similar in size, but these aren’t fruit flies. The gnats, themselves, are fairly harmless to the top of the plants. They lay eggs in the growing medium, and these hatch out maggots, and it is these maggots that feed on the roots and damage them.
These larvae will chew and strip roots and will destroy your crop. In the Mom tent, they were even more damaging, because these are plants I’m hoping to keep. I had them before, years ago, and this is my first redo; I had forgotten everything, and back then my journals were non-existent and sketchy, even when I did keep records. The only way I realized back then that I had a problem was when the damage appeared in the plant tops. I had deformed leaves and shiny leaves (not a revegging). The issue was corrected, but I lost a month of veg time.
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Luckily, I have prevented the infestation from spreading to my other tents. However, my nursery and flowering tents are both fairly sterile and lacking in anything that the gnats like to eat. The Mom tent was grown to bud and then stripped and revegged. It was in this stage the gnats appeared, because they love to eat on old buds and stuff that end up below the new leaves and growth.
"Fungus gnats develop through four stages —egg, larva (with four larval stages or instars), pupa, and adult. The tiny eggs and oblong pupae occur in damp organic media where females lay eggs and larvae feed. At 75ºF, eggs hatch in about 3 days, the larvae take approximately 10 days to develop into pupae, and about 4 days later the adults emerge. A generation of fungus gnats (from female to female) can be produced in about 17 days depending upon temperature. The warmer it is, the faster they will develop and the more generations will be produced in a year."
The first step was to identify the pests. I put up sticky traps and verified the infestation and the culprits as fungus gnats.
The second step was to spray the plants with insecticide; I used Mighty Mite because it kills everything. But only on top. The fungus larvae were in the roots. And from the numbers of gnat carcasses on the flood tray, the traps and the floor, we were barely in time to stop this from getting out of control.
Third, I put Mosquito Bits on top of the coco substrate and mixed it lightly in the top. Mosquito bits will kill fungus gnat larvae, because it contains BT – Bacillus thuringiensis var. Isarelensis. Just make certain the bits don’t get in the reservoir, or you will soon have a white mold overtaking everything. There are other methods of administering this stuff – look it up online. I chose Mosquito Bits because it was cheap. And I can use them from the beginning in the coco/perlite as a preventative.
Fourth, I used hydrogen peroxide as a drench and poured the mixture into each pot. I am using coco/perlite, so the main focus was on the root ball at the bottom of the pots. It has been found that neither coco coir or peat moss are of any use in inhibiting the fungus gnat larvae from growth and completion. (Evans, Smith, & Cloyd, 1998). However, an 8 percent solution of H2O2 will kill the larvae eventually.
Fifth, I put AZAMAX in the reservoir. I used a four ounce bottle of concentrate for my 10-gal reservoir. It turns the water to milky white, but it kills a broad range of larvae, naturally, with Azadirachtin A & B as active ingredients and more than 100 limonoids.
I did overkill on this because I don’t want to have to tear it all out and start over. I have taken preventative measures in the other tents.
[1] This is why you won’t be sorry if you keep records. This is also why experience is important, and emphasizes the suggestion that new growers start slow and small and work through problems in miniature, before they invest in large grows.
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