Despite being a hardy, flowering plant that grows on three different continents in a wide variety of colors and scents, hydrangeas do get a few diseases that can make them look unattractive and even kill them. Many of these diseases come from fungus or from locations where hydrangeas are growing that receive too much water or too little sunlight. Knowing the symptoms of these diseases can help those who are growing hydrangeas identify the sickness and work to cure it, helping to restore the hydrangea's natural beauty.
This Hydrangea disease most commonly affects the Bigleaf Hydrangea. It is, as the name describes, a powdery coating on the surface of each leaf of the hydrangea, also causing purple splotches to appear. While this disease will not kill the Hydrangea, it will make it look pretty unattractive. This usually occurs with Hydrangea growing in to much shade or under high humidity conditions.
Brown, discolored leaf spots on the leaves of Hydrangeas are caused by fungal infections to the plant. These infestations will rarely kill a plant but brown splotched leaves are not very attractive, especially in a garden that people see regularly. This most often occurs in later summer months, with plants that receive a large amount of sunlight.
This is one of the few diseases that will actually kill Hydrangea plants, the most common being the Armillaria root rot. The leaves will appear wilted but will not recover event when watered and cared for regularly and will eventually die. This root rot disease usually occurs in Hydrangea plants that have poor soil drainage, so if this keeps occurring then that is most likely the problem.
Sometimes spores and fungus will grow on the undersides of Hydrangea leaves, usually towards the end of the warmer part of the growing season. This can be temporarily cured by rubbing off the dust on the back of the leaves, but there is no guarantee that the disease won't return.