Is this septoria leaf spot? I have already sprayed with Captan...hopefully that will do it.
Spots on Hydrangea leaves
Please post a photo.
Sorry, not sure why the original didn't post.
From what I could gather it seems to be Circospora. Please see the attached result from Google and use the first link. It has photos and the remedies are about 1/3 of the page down. Good luck.
http://www.google.com/search?hl=en&source=hp&q=dark+spots+on+hydrangea+leaves&rlz=1R2GPEA_en&aq=0&aqi=g1&aql=&oq=dark+spots+on+hydrangea+&gs_rfai=C_qS7kOl8TMDtMKmMzATemfRgAAAAqgQFT9Dj8sI
Thanks...really helpful.
It's definitely a fungal disease of some sort.
"Circles with dots, fungal you gots", LOL.
Captan should take care of it. If next year is more dry for you, it should not be as much of a problem. Be sure to rake your leaves up after they fall off the plant this fall.
I love that quote...I will remember that for sure. Should I cut off diseased leaves?
It would be a good idea.
Chances are it's really not going to hurt the shrub. It's just unsightly, unless it really gets bad. And I expect if you treat it with Captan or another fungicide it will be fine next year.
Good sanitation or cultural practices may help minimize the problem, but if it is Cercospora, it will not go away as you can only treat infections, not cure the plant. For example: throw the infected leaves in the trash, not the compost pile; to further minimize fungal diseases, do not water the leaves if possible. Instead, water the soil early in the mornings; do not plant the shrub close to other shrubs as this reduces air flow in between plants; pick up plant debris under the shrub; throw away dried out leaves and blooms in the trash when the plant goes dormant. If a large amount (more than a third) of the leaves have spots and you can afford it, replace the mulch near the shrub to reduce the number of spores in there; do not overwater as this keeps the area under the shrub wet too long, which helps the fungi grow.
Good advice, Luis, as always.
I'm not really sure it's even Cercospora, as I don't see the typical purple maroon bleeding from the circles.
But if it is, here's some more info on it.
Defintely do not do any overhead watering, as Luis has said.
But I've never had fungal disease that seriously harms the plants, especially when I spray with baking soda, or a fungicide. Seems one year they will get it, the next year if it's drier the plant will be realtively disease free, you might see some on the leaves at the end of the summer.
http://www.uaex.edu/Other_Areas/publications/PDF/FSA-7570.pdf