@Lewd101 is correct. Below is a re-post my gnat prevention and infestation strategy from the first week my current diary (
growdiaries.com/diaries/165223-grow-journal-by-negotiatebubble/week/926585). I alway add BTi to my nutes each feeding:
🚜 Kill Any Tag Along Pests on the Clones
‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Clones arrived in mineral wool “rockwool” cubes. Before these clones entered my sacred space, I swirled each one in the Neem Oil solution to kill any tag along pests:
NEEM OIL SOLUTION:
Before adding most of the water, mix together a tiny bit of that warm water, ¼ tsp dish soap and 10 ml Cold Pressed Neem Oil.
Then, pH 56oz / 1.5L of warm water add it to the neem/soap mix.
Cold Pressed Neem Oil is different than cheaper heat processed neem oil because it still contains the natural Azadirachtin (same active ingredient that is in AzaMax pesticide). Also, neem has a weird property in that is kills a lot of the bad pest in the soil without harming good things in the soil food web like nematodes, protozoa, anthropods, etc.This is why it makes a great soil drench for gnats as well. During a gnat outbreak treatment, I will spray the neem oil solution on top of the soil to stop the adult from laying eggs
Organic Neem Bliss 100% Pure Cold Pressed Neem Oil
https://www.plantonix.com/neem-oil.php
🚜 Gnat Prevention
‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
I hate fungus gnats.
I will only be watering the mineral wool “rockwool” cube itself plus watering about 8cm or so of the soil around the cube to avoid having the dry soil wick all of the water away. It even more crucial that I avoid watering any soil that is not yet occupied by the root system. That unoccupied soil will just stay wet, which grows fungus, which attracts fungus gnats. This is why a good rule in later weeks (Weeks 2+) to let the plants go a bit thirsty rather than risk overwatering. It does not rain on schedule in the real world.
A fungus gnat spends most of its lifecycle as a larvae, not the adults that you seen flying around. This is why yellow sticky traps should only be used to monitor for infestation since only catching the gnats in the very last part of their life cycle will not help. Non-adult gnat larvae will eat the root tips of your seedlings and starve it to death.
After I transplanted the clones into Happy Frog soil in 5 gallon fabric pots, I added a solution of BTI (Bacillus Thuringiensis subspecies Israelensis, aka Mosquito Dunks brand) to the watering container each feeding to kill any larvae based pests such as gnats. Mixing Mosquito Bits into the soil before planting is also a great idea.
https://summitchemical.com/products/mosquito-dunks
https://summitchemical.com/products/mosquito-bits