So at the end of spring (maybe at the beginning of summer) our sour cherry tree started producing these yellowish/brownish spots on its leaves. Can you help me identify the couse of this? What can we do against it? I cannot see any bugs on it, my best guess would be some kind of a fungus, but I am way far from being an expert. Thank you in forward for the answers!
Edit: I am located in Hungary. The brown spots are not bigger than my nails, but the yellow area can cover even the whole leaves. Also, the capillaries visible on the leaves can turn red, as you can see on the pictures. Unfortunately, the exact species of the cherry is unknown to me.