Diseased outdoor plant

[Bennyisback]

Hi I’m Ben. I have a mature outdoor plant which seems to have a disease that is happening since it started flowering.

 

[Bennyisback]

I have noticed black spots on stem and leaves. Thrip/ scale?? Sprayed white oil. The damage happens within a week of being healthy to dead as seen in pic.
Using Nitrosol for fertiliser

 

[jetbtkng]

somebody should be able to help u, to me looks like poisoned, something bad happened to it...