I don't know if neem oil is effective for fungus gnats. My one-two punch with fungus gnat is to use the BTI or mosquito bits in the soil and combine that with the sticky traps to catch the adults.

Neem oil can kill fungus gnats. BTI (gnatrol) seems more effective in reducing the larvae population quickly though. My problem is there are still adults (very few but even one is too many in my eyes) around after the 72 hr period and more water is the exact opposite of what the plant needs.

So I’m looking for something to use in combination with the gnatrol that won’t negate its effectiveness.

I have not found any scientific studies that address this question. However, some scientific studies have shown that neem extract has antimicrobial properties. So neem oils, especially those containing azadirachtin, may inhibit BTI growth. However, the insecticidal BTI is in the form of endospores, which are resistant to chemicals as well as other antimicrobial agents. In other words, neem oil may inhibit the growth (multiplication) of BTI vegetative cells but should not kill BTI endospores. So, the endospores should be viable when ingested by fungus gnat larvae and should therefore kill the larvae.

I know what you mean about one is too many up the nose. So disrespectful!

I use the dry mosquito bits so I don't have to add extra water to the plant. I just mix it into the top inch of the soil. I also use the sticky traps to trap the adults.

If you have the patience for them, carnivorous plants can also be effective.