Ask-a-Dave's-Gardener: Half-sick Phlox, 1 by pegoplant

pegoplant wrote:
I have a tall garden phlox (usually blooms August-Sept.) that grew normally, but now the middle part is curling up and dying. The rest (outer part) looks fine and is about to bloom.

My Laura phlox 3 feet over started okay but then curled up. The Red Riding Hood phlox in the same area is all healthy and in full bloom.

What could be troubling the first phlox? It's not the best growing weather here this year (colder and wet) but the fact that only part of it isn't happy is puzzling.