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:
http://www.dealfaro.com/~luca/oak_leaves.jpg
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!
Luca
(You can also write me at luca ;at; dealfaro ;dot; com, which works better than my yahoo address)
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