http://garywinder.com/rhodies.html

Thanks

Bud blast is a disease that causes buds to discolor and not open, but in this case the buds usually persist unopened on the shrub and are not prematurely dropped as you describe.

Petal blight - Water-soaked spots appear on the flowers which become soft and brownish. "The fungicide Bayleton has provided satisfactory protection when applied to the flower buds as they begin to show color." - American Rhododendron Society. In the case of petal blight, its important to remove infected flowers, avoid overhead watering, and apply good sanitation, keeping any litter beneath the plant picked up....wind, rain, irrigation may spread the fungal disease.

Do any of these symptoms apply to your shrub?

And, beware the gardener/contractor who thinks fertilizer is the first defense for any problem. The only problem fertilizer will address is low fertility :)