Hard to tell with that quality pic. Likely fungal. Spray with a fungicide or neem.

Dan

Hmm. Well here's another opinion.

I doubt that's a disease. But a closer view might help determine that.

Here is a link that might be useful: the image

posted close ups
http://forums.gardenweb.com/forums/load/hydra/msg050934293657.html?2

Interesting challenge.

That might be an obligate Pseudomonas leaf spot taking the opportunity to propagate from the weakened defenses caused by some environmental factor, judging by the (dis)coloration pattern. I'd verify the soil is well-drained and has good OM and nutrients available. I wouldn't wager on this diagnosis with the paucity of info given, but that's my 2¢ at this point. I'm still happy with fungal as well, with just some necrosis here and there from the moisture stress, and some of that discoloration indicates moisture stress.

Dan

Wow, Dan , that's a mouthfull of terminology ;-) Thanks. I know the drainage is good and I mulch the area around it. We did have lots of rain, but it also get plenty of morning sun till high noon. Should I feed it with some particular nutrient? Any spraying needed?

My other, older and bigger hydrangea is simetrically on the other side of the door, so it faces the same way, but it gets a dappled sun in the morning and afternoon. I noticed couple smaller brown spots on its leafs too. Otherwise, the plants look healthy and flower.

Sorry, in my own little writing world right now. Apparently I didn't come out fully when I wrote that upthread...

Never fert a stressed plant, and I don't know that anything will really fix the fact that some leaf tissues died and the decomposers are moving in, as we expect.

I had a Philadelphus get hit a couple weeks ago with a little fungus (very odd here where we expect single-digit humidity). I squirted with neem and removed a couple branch tips and it took care of itself. If yours spreads to more leaves, remove affected lvs, coat the plant with neem around dawn or dusk, otherwise it should just run its course, hit a few lvs and go away - provided the diagnosis is correct...probably lots of that in your part of the country this year.

HTH.

Dan