My hydrangeas were beautiful until about a month ago. I noticed one of the plants had a shriveled branch, while the rest of the plant appears healthy. This has progress to 4 branches and I am seeing the same thing on several other Hydrangea plants. I checked to see if the branch was broken, chewed, or damaged in any way. There are no noticeable insects or other pests. I have included a picture of the first plant that developed the problem.
Our plant pathologist looked at your photos and thinks that this is a fungal disease known as Botryosphaeria.
It shows up from time to time and a typical symptom is scattered dying branches on an otherwise healthy plant. Leaves on infected stems droop and roll, then turn brown. These leaves often lay flat against the stem and will remain attached. The pathogen can infect all ages of stem tissue through wounds, pruning cuts, and leaf scars. Heat, drought stress, and winter injury can increase disease incidence. Cankers on branches can gradually grow through the wood until the stem becomes girdled.
Prune out the affected branches in dry weather, and dispose of them out of the yard.