was it grown in a greenhouse ... or did you change some of the cultural variables by putting it in one??

like reduced sunlight thru glass and increased humidity??? .. etc ... how the pot dries ... etc ..

ken

Looks like the start of bacterial leaf spot aka bacterial shothole. If this develops late season, there is typically little cause for concern. Just gather up all the foliage when it falls and destroy - do not compost.

A dormant season spray regime may help for an early infestation (which can travel to stems and branches) but you would need to refer to local sources about the need, timing and product to use in your area. I am not much help for the UK :-)

thanks, you gave me a starting point and I may need to adjust my watering so it doesnt hit the leaf. The mister may have caused the problem. I will turn to a dripper and see if it halts the problem.

I have been researching and here's my first line of attack.

https://migardener.com/prevent-kill-blight-powdery-mildew-baking-soda/

One of which I've seen used before, the idea is to create a PH environment that kills the fungus without harming the plant. A simple and cheap solution which wont remove the damage obviously, however I will be treating my trees in the winter with an organic fungicide that's safe to use on fruit trees planned for consumption. To see if I can cure it before its a complete total mess.

Any other tips are greatly welcome being such early days in owning fruit trees its been a bit discouraging but I'm not a quitter and ... "You've not lost until you've quit." So fight on.

Is there an amount of foliage removal that could damage the plant? I would say I've take 10-20% maximum off so far but I could remove more.

Those leaves will drop naturally in a couple of weeks given the time of year. Don’t remove them and when they fall don’t compost them. Look into proper winter washes and forget the homebrew YouTube concoctions. When you water, water the soil, not the tree, and keep the greenhouse ventilated in winter. Also make sure you get information intended for U.K. conditions and pesticide regulations. Blogs aren’t the most reliable place.