It could be that they have been dried by the sun, but thick it could be a mite issue. Confidor is not a good mite killer so you may need to check under the leaves for mites.
If its not mites I will watch the post with interest for another diagnosis.
I think too many sunbeams . I had one growing in the ground and every year at this time of year it looked like this . I dug it up in spring and I'm growing it in a lot shadier position and this year it's still pushing growth . They don't like to dry out .