Wow. There are so many diseases, weevils and general nasties that attack rhododendrons. Not sure what this one is but if it isn't too late I seriously suggest you get rid of those weeds
. They act as a home for many bugs. I suggest you check diseases of rhododendrons on Wikipedia and also look on http://www.apsnet.org/online/common/names/rhododen.asp
which lists a few. The accepted U.S. authority is Ohio State University and you might like to browse round http://ohioline.osu.edu/hyg-fact/3000/3043.html
I don't know what your winters are like or what zone
Oklahoma City is in but, if you get heavy freezes in winter there is a just a possibility that it is suffering from freeze drying (no not like your instant coffee). Rhodas are evergreen but don't like being dry even in winter. The symptoms are browning of the leaves but I am rather more worried about the white spots, which have an aura of a fungal infection. If it is freeze drying then it should recover as the new growth starts (although freeze drying slows that as well). Let's hope that it is and if so then water it well in late fall this and future years, before the first freezes. But with the small amount of info we have the definitive answer is that we just can't tell.
Sorry I can't be more help.