Answer: Unfortunately, based on your description I am not able to give you a firm diagnosis of the spots. There are numerous problems that can cause dark spots on hydrangeas including Cycospora and Anthracnose for example, but it is very difficult to diagnose this type of symptom long distance. Since these are brand new plants I would strongly suggest you contact your retailer and/or your local county extension for advice. They may appreciate a photo of the overall plant and closeups of the discoloration as well as a freshly cut sample kept cool and enclosed in a clear plastic bag. If a chemical control is needed, the extension staff will have the most up to date information on what to use and when/how is best to apply it.
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