It is difficult to say without seeing them. It may be due to an insect sucking on the plants. Your best bet is to take some leaves showing the damage to your County Extension Office and see if they can identify the cause of the damage. They would then be able to recommend an appropriate, labeled product for you to use, if one is indeed needed.
In the meantime try shearing them back by about a third and then giving them a few weeks of fertilizing with a soluble product such as Miracle Gro at the label rate. They may turn around and be back in bloom within a month.
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