I purchased 2 endless summer hydrangeas this year. I planted one in the front yard, one in back.They both developed a rust color to their leaves and brown circular spots. I went to my local nursery and described these symptoms and he gave me a product to control rust, fungus and black spot. I used it faithfully but did not see any improvement. I mulched last week and stripped the plants of any remaining leaves and raked thoroughly to remove any leaves that might be on the ground, then mulched. I am not sure if I can cut this plant back or if it reblooms on old wood. Can anyone give me any pointers? It will be much appreciated
I'm not familiar with the disease, but you shouldn't cut back anymore now as you won't have any blooms next year. Wait until they bloom and then cut back. I'll try to do some research and see what it may be and what you can do. Could be a leaf spot and something that won't really affect it much.
There is a photo you could compare to. An extract from this article says:
Finally, don't be alarmed if the leaves of your `Endless Summer' become covered with purplish-edged spots in mid- to late July through the end of the season, below left. The spots are caused by a very common disease that infects young leaves as they're expanding during wet weather in early spring. The disease is harmless and may not occur in years when spring weather is on the dry side.
And another article says you can prune in later winter and after blooming. ES will bloom on new and old wood.
It is probably cercospora leaf spot. Unfortunately, it is pretty much impossible to get rid of...you just try to control it. You have done the right stuff, so far. Another help is try not to water overhead. I start spraying mine at the beginning of leaf development. It is harmless, but can look bad if it gets too abundant.