Here are a few more pics

Another view

Look closely on the back of the leaves. My guess is you may some something sucking the juice from the leaves. Maybe spider mites. If it is mites, you can spray with a miticide or some people use a diluted mixture of hydrogen peroxide.

This post was edited by kidhorn on Fri, May 30, 14 at 11:00

Spider mites should produce the tell tale spider webs once they reproduce enough; they can also cause leaf curling on new growth as they prefer to suck the tender new growth. They are tough to see as they are tiny but, you can shake the end of the affected hydrangea stems on top of a 8x11 white paper to see if you detect tiny dots that move. If you confirm that, you can use a hard spray from your nozzle to dislodge them violently enough to kill them. You can also release beneficial insects like ladybugs or even use a miticide.

Consider chemical exposure too. When another bush far away has been sprayed, the winds can cause some of the chemical to end up on the hydrangea and the new growth would be harmed more than older leaves.

Cercospora fungus would be a possibility as it starts with similar brown spots but it develops purplish lesions as the leaf damage gets older. It is rare to see it at this time of the year but it may have been acquired at and transmitted from the wholesaler. If you have a magnifying glass, you could try to see if the affected area looks like spores.

Luis

This post was edited by luis_pr on Fri, May 30, 14 at 21:18

Update: I consulted with a plant pathologist from TN who said the damage could be caused by an insect called a four-lined plant bug, similar to one on the variegated hydrangea picture in the link below. You would have to catch it doing the damage to confirm of course.

Here is a link that might be useful:

This post was edited by luis_pr on Sun, Jun 1, 14 at 3:05

I'm a little late but that was my guess too. Since I have them, I recognized the signs. The babies are little red nymphs and they run under the leaves. They like the fresh tips. Just take your hand a little down the stem, below the damage and run your hand just hard enough to crush them but without damaging the plants. They like many different types of plants.