Escalonia hedge yellow leaves every autumn

Hi
Cousin of mine has a escalonia hedge planted afew years ago every autumn some leaves turn yellow and some have spots , I have previously advised need to pick up and bin yellowing leaves , and it's has been feed earlier in the year , what can be sprayed on the hedge to spot this happening? Can I use potassium bicarbonate solution?
It is a inland location which I understand is not ideal for this type of hedge

 

It's perfectly normal for that to happen. All evergreens drop leaves or have some yellowing, spotting, discolouring and dying off.
They can grow well enough inland, so it's not down to location as such. It's just that they're particularly useful in coastal areas where other hedging shrubs can be affected by salt spray and winds, as well as the sandier soil. They like good drainage and a sunnier site, so it can happen more if they're a bit shaded.
The white ones are less tolerant of everything - especially colder, wetter areas.

 

If the leaf yellowing is quite contained and the plants recover every year, I wouldn't be worried. The red variety, E. rubra, grows very well here in coastal sites and is often used for hedging. There's one I walk past on the top of a cliff which always looks healthy, despite the battering by the wind. If the leaf spot becomes widespread, it could indicate something more serious but it doesn't sound like the description here:

Escallonia leaf spot / RHS