Our beautiful hydrangea tree, which is 10 years old and a stunner every year, is shedding leaves. They are turning yellow and have green splotches and black dots on them. This has never happened before. We think the tree may have a blight or pest. Can you advise, including any treatment method. The tree usually flowers in August. Thank you.
Thank you for contacting Toronto Master Gardeners about your beloved Hydrangea tree.
We have not found the pathogen responsible for the yellowing, splotching and defoliation of your hydrangea tree leaves however, the small black dots evident on the splotches are the organisms causing the problem. The following article developed by The Missouri Botanical Garden provides good information about the general problem. The Purdue University and Illinois University papers also address the issue.
The takeaway from these sites is the necessity of removing all fallen leaves and pruned out dead twigs for disposal outside of your property, including the autumn leaf fall, keeping the tree healthy by fertilizing if needed. Unfortunately we have no control over our wet spring weather which fosters this infection.
We wish you well in cultivating your tree back to full health and bountiful bloom later this summer.