Our vine is ~3 yrs old (in our garden), with northern exposure. Earlier in the summer leaves near the bottom appeared to be eaten around the edges (my guess is earwigs), mid-summer the plant began to look less hale, not having produced much growth, then this past week, leaves higher up the vine appear to have some leaf spot (brown circles, surrounded by a burgundy ‘pool/halo’. From my recent research, perhaps it hadn’t got enough water, but now I read that the leaf spot results from too much moisture and lack of air circulation. The plant is not that dense. I’m baffled and would appreciate the benefit of your expertise!
Your climbing hydrangea has developed leaf spot disease caused by the Cercospora hydrangea fungus. Foliage and flowers affected by this fungus develop brown and purple spots. These spots first appear on lower leaves and works it way upwards as the disease progresses.Leaf spot fungus begins its attack in late summer, and gets progressively worse through the fall. If the fungus is allowed to spread unchecked, the affected plant will stop growing, defoliate and produce sickly-looking flowers. The fungal spores on the fallen foliage will transfer to healthy areas of the vine and onto other shrubs if the infected leaves remain on the ground.
The best way to manage the disease is to gather up and remove all affected leaves and blossoms. Applying nitrogen to the soil to encourage the vine to thrive and produce new growth and surface watering will help slow the development and spread of the disease. A fungicide purchased from your local garden center can be applied as soon as you notice the spots.
The following is a website with additional information on hydrangea leaf spot disease