Sweet cherry trees are not easy trees to grow. They are susceptible to many diseases and insect problems. Leaf spot, bacterial canker, brown rot, shothole, and powdery mildew are just a few of the diseases that affect sweet cherry trees and that does not include several root and crown rot diseases that include phytophthora root rot and crown gall. Insects that are common to cherries include scale, aphids, spider mites, cherry fruit fly and spotted-wing drosophila. Because of all of the possible problems you should be prepared to spray your tree several times a year in the hopes of keeping it healthy. Otherwise, you will probably need to replace it within a few years.

While your sweet cherry tree does have signs of leaf spot or shothole with the brown spotting and yellowing of some of the leaves, it that does not appear to be what is causing the entire tree to decline. There are no noticeable cankers on the trunk in the pictures, so bacterial canker, a very common disease of cherry trees, can probably be ruled out.

This tree looks to be water stressed. Cherry trees need well-drained soil. While they are very sensitive to waterlogging, they do need to be watered deeply (2 to 3 feet down into the soil) at least monthly, bimonthly is ideal, during the dry season and particularly during the months of July and August. Your cherry trees are close to pavement which makes it hard for the entire root system, which extends out to the drip line, to have good access to rainwater and irrigation. It is also recommended to place mulch on top of the soil to reduce evaporation. Be sure to not place the mulch next to the base of the tree.

If you feel your cherry tree is well-watered and not water stressed. With the symptoms you stated and what can be seen in the pictures Phytophthora root rot is one other possibility, a fungal disease where the roots of the tree are decaying. Information on this disease can be found at Cherry (Prunus spp.) Phytophthora Root Rot.

For more on growing sweet cherry and other fruit trees the publication, Growing Tree Fruit and Nuts in the Willamette Valley, and a YouTube video from a recent Lane County Master Gardener Association seminar, Growing Tree Fruits in the Willamette Valley.