Horticultural oil will suffocate plants as well if used too often. It's hard to give a maximum frequency, but small thin-leafed plants will be much more susceptible.
I don't use oil much because I have good results with soapy water and alcohol. However, I mail ordered a Passiflora two years ago and it came with a type of scale I hadn't seen, Florida citrus scale. This is reported to be susceptible to neem oil. Online reading about treating passion flowers suggested not to use oil more than twice in a month.
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