Cleary's Spectro 90 WDG is labeled for hydrangeas as long as you use correctly per product label it should not harm your hydrangea buds
Clearys Spectro 90 WDG states on the product label: Not for homeowner use. Not for use on turf being grown for sale or commercial use as sod. Do not use on home lawns and turf sites associated with apartment buildings, daycare centers, playgrounds, playfields, recreational park athletic fields, athletic fields located on or next to schools (i.e., elementary, middle and high school), campgrounds, churches, and theme parks.
Clearys Spectro 90 WDG is a water dispersible granule that works both systemically and on contact applied directly to the plants. Please note that this is not labeled for residential use.
For smaller spot treatments, Clearys Spectro 90 WDG is applied at 1-2 tablespoons per gallon of water. Make sure to spray thoroughly as this product is a contact fungicide. **Not for homeowner use. Not for use on turf being grown for sale or commercial use as sod. Do not use on home lawns and turf sites associated with apartment buildings, daycare centers, playgrounds, playfields, recreational park athletic fields, athletic fields located on or next to schools (i.e., elementary, middle and high school), campgrounds, churches, and theme parks.