Same rhododendrons, same exposure, same bed, two failing - would point first to the planting technique. A guess would be the roots were not loosened when they were put into the ground and are not getting adequate water. If the root ball is still tightly in the shape of the nursery container, it's easy to wet the soil around it with no water penetrating the root ball.

Fertilizer could also have burned enough roots there are not enough left funtioning to supply water to the top growth. Or, rhododendrons that have had more time to establish may be more tolerant of your recent heat, assuming yours are more recently planted....

My azaleas and rhodos are mostly dead, now. They were planted in the shade, bloomed beautifully this spring, then became dried up, leaves curled up, and they apparently died.

I think the problem is root rot. What do the rest of you think?

Thanks for the replies. It might have something to do with the roots. The only thing that I could've possibly done to hurt my rhodo's was put down more mulch. We were given barely enough mulch in all of out flower beds.
I only added about 1/2" loosely around the rhodo's base & bed. My neighbor did not do this. When the landscapers stop by again, I will have him pull up the plant & inspect the root ball.
We have a bed between our walkways filled with lirope. Last year, it was flat & did not bloom. This past spring, I added more mulch around each plant, kinda to give it some kind of boost, because the things looked like spiders, they were so flat. Well, that was a success, with watering & rain, this lirope is gorgeous. It has its light purple blooms & all of the plants are standing up, looking happy & nothing like the spidery stuff of last year.
One more question, is there a reference somewhere on how to plan a full sun flower bed with plants or bushes that looks nice most of the year?? I'd so love to re-do my front bed & have it looking great.
Thanks again, Babs

I think the previous posters are on the right track: too much fertilizer on stressed plants or improper planting could have contributed to the problem. It sounds like you didn't get carried away with the mulch which can sometime lead to fungal infections/insect infestation if piled around the base of the plant. Other known problems with Rhododendrons like clorosis (iron deficiency/high ph) rhododendron borers, or winter desiccation obviously are not the relevant. To determine the problem more accurately you may want to submit a sample to your local cooperative extension.

Regarding brademac z6 NW:
It could be any of a number of problems. Root rot generally occurs when there is an abundance of water particularly if the plant has been stressed by drought prior to such. If they were planted in a moist area or one with poor drainage root rot may be the culprit. Otherwise I would say that one of the above problems may also be the problem.

beachbrat26, is it possible you have turf grass nearby your shrubs? If so, I'm wondering if any type of fertilizer, pesticide, or herbicide might have been used and overspray hit your plants but not your neighbor's?