What about a waspinator as a repellent.
Yes it on Prunus laurocerasus too, I have a laurel hedge which has also got a lot of wasps at the moment.
Wasps are attracted to laurel leaves as they produce a sweet secretion from two ducts on the back of the leaves.
The most likely reason for the black on the leaves of your camellia, is that is has scale insects, you should be able to see them on the under side of the leaves, if you can see them you will have to use an insecticide.
I not that keen on using chemicals in the garden either, but they do work better if the problem is bad. I use it on a large elaeagnus in my garden with the same problem, It works for quite a while , but the pests do return. You could try an organic pest spray .
I would use a systemic insecticide on the elaeagnus.
There are some x hose and pocket hose repair videos on YouTube.
To me it looks like the leaves have got wet, then it has got scorched by the sun.
I grew watercress a few years ago in my greenhouse, I just used some wide plant pots in a tray of water, they did quite well.
Looks like a cricket.