I think your plant is ok -srt of-, caramlefloat. As we approach reduced light levels and cooler temperatures in late summer to early Fall, chlorophyll production goes down and the leaves begin to shut down and turn ugly. The leaves turn different shades of greens and yellows. Leaf spots that may have been "invisible" before then become visible and show some purplish/brown/dark colors in blotches throughout the leaf surfaces. Eventually, the leaves will eventually brown out and dry out.

The browned out, dried out leaves eventually fall down on their own. I have one shrub that did this already and it too suffers from leaf spot. As the leaves started to fall or brown out, I either picked up the leaves from the floor or cut them at the petiole. The petiole is the stalk that connects the leaf to the stem. I do not cut the stem (especially the ends of the stems) because that is where the invisible hydrangea flower buds for 2015 reside. I then throw away the leaves in the trash (not on the compost pile where the leaf spot fungi could spread). If the leaf looks nasty enough, you can accelerate the process by cutting it away now. The point is to prevent the spread of spores (as much as you can) when the leaves fall down and decompose.

Other things that you can do:

Always maintain 3-4" of mulch up to the drip line or a little further. Try not to overwater. Minimize overhead waterings to reduce leaf spot and powdery mildew. Replace the mulch with new mulch in cases where the leaf spot infestation is severe. Remove plant debris under the hydrangea to reduce places where the fungi can reside. Reduce moisture levels if they are high since fungi likes high humidity levels; examples of high humidity: plants in the area may suffer from fungal infections or the soil may appear to be wet often. Water the soil early in the mornings (as opposed to watering the leaves). For a plant such as yours, I would water 1 gallon of water per watering.

There are some fungicides out there that one can use for Cercospora Leaf Spot (aka, leaf spot) but they can be expensive and, at this time of the year when the leaves are falling & shutting down, it may not be worth it. See additional information on Cercospora Leaf Spot on the link below.

Luis

Here is a link that might be useful: Diseases of Hydrangeas

This post was edited by luis_pr on Tue, Dec 9, 14 at 9:08

Thanks so much for the detailed tips, luis_pr!