Plants are more susceptible to problems such as mildew when they are not in ideal conditions. Perhaps needs to be taken out of the shade and put into the sun. Mildew that is powdery will likely come when things are too dry --- but still need some sunlight.
Powdery mildew is a fungal growth caused by humid conditions, either from rain, too much watering or inadequate pruning to allow for adequate air movement.
Plants are more susceptible to mildew when they're stressed, which could be too much shade, drought, etc. Honeysuckle mildews often strike when things have been too dry. )
