hydrangea macrophylla zorro

Sounds like mildew. Blame the weather. Either use a suitable fungicide (some are not recommended for Hydrangeas) or try spraying with 1 part full cream milk to 9 parts water. Also keep them well watereed, dryness at the roots can sometime leave the plant open to mildew attacks.

many thanks for your advice - will try the milk and water first.

a very dilute solution of baking soda and water (two tsp. to a gallon) applied with a spray bottle works too... don't apply it to the soil...just to the dusty looking leaf surfaces...