Garden Pests and Diseases: Flaky white stuff on hydrangea leaves, 3 by erre

erre wrote:
Thank you hcmcdole for posting that link to the borer insect!

I was able to quickly figure out that this was exactly my problem. I found three canes with holes at the top. I cut them and opened them up transversally. There the insects were!

It seems like this is it, but I will keep making daily checks to cut down all the infected canes. I was problaby fortunate enough to catch this problem early. There was definitely no white powdery stuff a couple of days ago.

I am posting some images.