15+ Brown Spots On Hydrangea Stems. Brown spots in the stems are normal on some hydrangea stems. If your hydrangea has brown spots or rings on its leaves, there is a good chance that it is infected with hydrangea ringspot virus.
Here's how to do it.
Cercospora infection will show as purple spots, rather than an overall purple cast to the leaf. You may want to cut back up. Also, thin out crowded and crossed over stems to allow better air circulation. Blue hydrangea with stems and leaves.