black leaves on hydrangea
Thanks for your question to Ask Extension. Has the plant been recently fertilized? Over fertilization can cause the leaves to turn brown and appear 'dry'. A photo would help with the diagnosis. Assuming fungi or bacteria are indeed the problem, be sure to remove all leaf and stem litter where the bad actors can winter over. Although it's likely too late for treatment this season, one reference recommends a half tablespoon of neem oil to a pint of tepid water for spraying on the leaves. This is short-lived and would need repeating (e.g. 7-10 days). http://www.aces.edu/pubs/docs/A/ANR-1212/ANR-1212.pdf is a reference showing photos of hydrangea disease and some recommendations you may wish to read. I hope this helps and please reply if you have additional questions.