Does rain affect neem oil applications?
Rainfall can effect the Neem Oil, but in most cases the application that you apply has all ready began to effect the sucking or chewing insects.
It's best to apply Neem Oil in the morning so the Neem Oil can dry before the good insects become active.
Avoid the times of day when beneficial insects are active, though Neem Oil is safe for them, they can still be smothered if drenched in Neem Oil.
Neem Oil also works systemically.
Here is a link with more information.