Coastal live oak illness?

I have a coastal live oak tree in my backyard, that until recently has been in great health. However, today I noticed some brown spots on the leaves - in fact, this is quite widespread. I posted a photo at:
Nothing very special happened to the tree recently. Below it there is some dry leaves-covered ground, and (not adjacent to the trunk) a lawn that is also somewhat dry. Recently, the gardeners put a small amount of fertilizer on that lawn, but that had been done before without ill effect.
Any idea of what this is? Thanks!
(You can also write me at luca ;at; dealfaro ;dot; com, which works better than my yahoo address)
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