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Hi. Most of the time this is a fungal infection to the leaves. The tree should be fine in the spring. As soon as sufficient leaves are on the ground, rake them and burry them or burn them. Usually the cycle for the fungi is to hibernate in the leaves in the winter on the ground and the spore fly back in the air when rain drop hit them in the early summer.
The trees have natural defences but a mineral deficency in the soil can weaken it and get it infected. For that reason i always spray wood ash on the ground at the end of each winter.
I don't know about the amount of rain you got in your area but in the East it was really humid and a lot of trees (especially prunus type) suffered from fungi infection in the leaves. If it come back to normal humidity next year, the problem may solve itself.
You also mentioned that the tree is big. Any fruit tree benefit from a bit of prunning to allow UV light and good airflow deep into the branches as this help control the fungi growing conditions. It also prevent the spores to climb to high in the trees at each rain by the ladder effect of using nearby branches to infect the one right up to it.