What is this disease or pest killing my plants?

The reason I dont like neem oil is, in my opinion, it blocks the leaves from breathing.
Works as a good leaf shine if only used on the top surface.

 

If you look at the info on Neem oil, it does say that it should be mixed with liquid soap to be used as an insecticidal spray. Cannot find the piece of paper which came with the bottle I bought, sadly.
Had no effect on root aphids either mixed or straight.

 

And I m thinking the soap has a more insecticedal effect than the neem oil.

 

I'm so glad that someone else has questioned the principle of spraying oil over plants! If it's copious/thick enough to suffocate the insects, I'd have said it's thick enough to block the stomata on the leaves, too.