Does this mean the tree is diseased? There are no spots or bumps or any other damage on the leaves, just the fall colour. Otherwise, the tree looks perfectly healthy and has lots of berries. It’s out in the open, gets lots of sun and rain.
Serviceberries are pretty tough plants. There are a few common problems to which they are susceptible; powdery mildew, which you can identify as greyish white spots and cedar-serviceberry rust, which presents as orange-red masses on the underside of the leaves, and yellow / orange / red/ brown lesions on the upper side. Eventually, the berries grow spiky red ‘fur’ in the case of the rust.
If there were many rough, pale, dark red-edged circular spots on the leaves, later becoming maroon before dropping off, that might indicate entomosporium leaf spot, a fungal disease that is most active in cool rainy weather, which we did have this spring.
However, since you say you see none of these symptoms and your tree seems otherwise healthy, I think that what you are seeing is a normal colour change and drop of the oldest, non-productive leaves. If a large number of the leaves demonstrate this behaviour, it can indicate stress, most often, the result of drought … again, certainly not the case this spring!
Keep an eye on the tree and if more symptoms appear, or a lot of leaf drop, please contact us again on this web site, posting a picture.