Tolerance plays a key role in gardening. As a Master Gardener, I am constantly being shown leaves with spots on them, insects that devoured ONE leaf, a flower that wasn’t quite up to par, etc. You need a certain degree of tolerance. There’s no such thing as a perfect plant and there are literally millions of insects just waiting to feast on your plants.
Above is a picture of a hydrangea with leaf spot. This picture was taken in my own garden at the end of September. It obviously has a fungus, probably Cercospora. There are literally thousands of fungi spores in the air at any given time. With high heat and humidity you just cannot avoid leaf spot on your hydrangeas, particularly Hydrangea macrophylla and particularly this time of year. However, since this was September, not June, and the leaves are ready to fall, not grow, the condition is tolerable. This unsightly leaf should not cause you despair; leaf drop will be occurring soon. You can help it next year by raking up any fallen leaves now, dispose of them (do NOT compost), and water from below not above throughout the growing season next year. Generally these symptoms don’t rear their ugly head until fall, long after flowering.
By the way, here is what that plant looks in bloom, sans leaf spot.
So don’t sweat the small stuff and give yourself a break! Tolerate it! You’ll be so much happier in the garden.