Answer: The most likely reason would be drought combined with excessive summer heat. These plants need a humusy and acid soil that is evenly moist yet well drained, meaning not sopping wet. Using several inches of organic mulch over the root zones can help, but do not make it too deep because these plants are shallow rooted and like a well aerated soil -- this is also the reason they will not tolerate overly wet soil. If you think that soil moisture is not a possible cause, then I would suggest you take a sample along with possibly some photos of the plants and consult with your county extension and/or professionally trained nursery personnel as to what the possible cause could be. I suggest this because there are a number of potential pests and diseases that could bother these plants and they are difficult to distinguish without a sample to look at. Good luck with your plants.
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