Rhodendron Leaf Bottom has Brown/Orange Power
My Rhodendrom leaves have been looking sickly the last 2 or so years. Leaves are Dry and leathery on top with yellowing on the edges and black spots on the bottom.
On some leaves, I can rub my finger on the bottom of the leaf and pickup a considerable amount of dry powerdery material which is orange or brown. I have looked at the bottom with a microscope and found no insects apparent.
Leaf edges curl slightly also.
Anyone know if this is a disease? or is it possibly a soil problem?
thanks in advance for any help.