Q: something is causing my phlox to wilt and die. It seems like it is starting at the bottom of the plant and working its way up the stem. I have 2 or 3 clusters of phlox, and it is not affecting all the plants, but a select few in each bunch. It does seem to be spreading.
Sounds like asters yellow. Re read problems of perennials on Yardener.com. Remove infected plants - roots and all as soon as you see the symptoms. Spray the surrounding plants with Captain Jack's Dead Bug Brew (Spinosad) to kill off aphids or leaf hoppers that are spreading the bacteria like disease. Good Luck Nancy