I just soil drenched w/Pyrethrin last week, with no negative effects.
Leaves are still pointing to the heavens.
It's a last resort, usually after Promix sells me a bag of infected peat based medium.
One watering kills everything.
Shallow pans of water placed near plants with a bit of dish soap is my usual means of preventing and controlling gnats/aphids.
They go for the water, then immediately drown...and I enjoy watching.