Below is a link to information about Hydrangea diseases and their treatment, using commercially available fungicides.

Some other members may have a home remedy for mildew, but there isn't much that can be done for black spot.

You could do a search on this Forum for Hydrangea diseases, by clicking on SEARCH at the top of the Forum page and enter DISEASES in the search box. It will display all of the threads where they are mentioned. To limit the responses, enter a specific disease, such as mildew, black spot, etc.

Some cultivars of Hydrangea are more susceptible to mildew infection, than others. The only cultivar that I have, that ever had mildew was, 'Preziosa', the most well known cultivar for becoming infected.

Here is a link that might be useful: Hydrangea Diseases

Well... I am thinking that the same thing that works well on Roses, will work just fine for Blackspot and Powdery Mildew on Hydrangea.. And, that is a mixture of water, a tsp of baking soda and a few drop of Dawn dish liquid, spray on the plants.

Good luck to you!

The leaf spot that sometimes develops on hydrangeas is NOT the same as rose black spot, so it doesn't necessarily follow that the same home treatment will have a similar effect. Different fungal organisms will respond differently to various treatments.

Both powdery mildew and Cercospora leaf spot are encouraged by environmental conditions as well as stress so addressing either of these situations will go a long way in controlling their development or spread without the need for any fungicides, homemade or otherwise. High humidity is generally a key factor so avoiding overhead watering, allowing adequate air circulation around/between plants, not letting the soil dry excessively between waterings and avoiding too much shade will help considerably, as will practicing good garden sanitation (removing and destroying fallen or affected foliage) and mulching to conserve soil moisture and prevent fungal spores from splashing up and reinfecting. Cercospora is much more prevelent in the south with warm(hot) summer temperatures, high humidity and heavy summer rainfalls - it is rarely a concern in drier, more northern gardens except with stressed nursery plants which typically outgrow the problem once planted. And, because both are fungal diseases that appear late in the season, treating now will have no effect - fungal problems must be addressed before you see evidence, not when the symptoms are readily visible. Besides, hydrangeas are deciduous plants that are getting ready to drop their leaves soon - why treat now when they will all fall off? Just clean up well this fall or winter.

And FWIW, neither disease is fatal or even serious to the health of the plant - they are considered cosmetic only.

Hi...I hope someone can help me here....my hydrangea has developed white, crusty spots all over it, a bit like large breadcrumbs. They are on the stems & leaves and I cannot find any disease described which looks like what has afflicted my plant. Can anyone suggest what it might be - and any remedy, please? Thank you.