Question
I was unable to open your last response so I repeat:

I have lots of hydrangea in Lido Beach. They usually stay in bloom all summer with rich multi-colored blossoms. Now some of those rich blossoms are drying and appear to  e rusting. They get plenty of water and sun and others with comparable conditions are thriving. What should I try to do?

Answer
Hi Steve,
Thanx for your question. This could be anthracnose or another fungal infection.  Have you had lots of rain and/or fog lately.  Is the soild soggy or just moist?  If you are watering them more than once a week, I would reduce to once a week unless the soil is bone dry.  It it's just one plant that is suffering then it is most likely a fungal infection.  You can take a sample in to your local County Extension Agent and they can tell you what's wrong and prescribe a treatment if there is one available.  There's not a lot you can do about anthracnose and some of the treatments are rather harsh.  

Contact this office and I'm sure they can help you with this issue.

http://blogs.cce.cornell.edu/nassau/

I hope this helps.
Tom