Here are two articles that may provide you with you with some ideas: the first is about Rhodie care in general, the other is about leaf scorch which is often associated with increased summer temperatures. Good luck with your plant.
Oregon State University Extension has two one-page guides for explaining how to evaluate and care for your rhody. They list options for curing the nutrient deficiency and for routine care. You can view them at these links: http://extension.oregonstate.edu/gardening/node/775 and http://extension.oregonstate.edu/gardening/rhododendrons-and-azaleas-need-strong-acidic-soil