The lower leaves and unopened flower buds are disappearing from my impatiens. The plants are not wilting or turning yellow. Flower buds continue to form but never open. The new growth on the upper part of the plants is small but otherwise healthy looking. There seems to be a white powdery coating on the underside of leaves but it doesn't look like powdery mildew. They get morning sun and afternoon shade. The new guinea impatiens close by seem to be doing just fine. Any ideas about pests or disease?
I would treat with Neem Oil, as is works as both an insecticide and fungicide.
Here are some links for you.