i would guess spider mites ... google such ... you can not see them ... but you can find them ...

are they indoors...

the media is out of focus.. but might not be proper for a tree ...

are they seed from a yellow beech.. color is off otherwise ...

i highly doubt its a beech related 'disease' ...

ken

Thanks for your reply.

They are regular beech, so the leaves of other plants (and of this one too) were bright green. They changed color and are now like that, with those black dots too.

See also additional image in links (copy & paste in address line)

did you google SPIDER mites.. and find out how to ID if there.. and what was the result ...

and are they indoors.. and what is the media ...

stressed plants are prone to many things... but unless you solve the stress .... the problem might not go away .. and i would not spray things on stressed plants .. the double stress might kill it ..

the buds look nice ... and that is the future ..

ken