Our roses are developing dark spots on their stems. Is that a problem?
You may be referring to cankers on your rose stems. Cankers can kill the living woody tissue in branches/stems. Control requires pruning back to healthy tissue. No chemical controls are effective. Keep plants well watered during dry periods. See our website for photos and more information https://extension.umd.edu/learn/cankers-trees-and-shrubs
Rhododendrons - See our publication on azaleas and rhododendrons and look at Botryosphaeria Dieback, a fungal disease. Look for diseased reddish wood along the branches. Control involves pruning, good site selection when planting, and proper maintenance. http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG51_IPM_Azaleas_and...