Answer: Nandina is susceptible to powdery mildew, especially in areas where air circulation is poor. Powdery mildew is a fungal disease which, if left untreated, can defoliate a plant. You can spray your plants with a fungicide to stop the development of the disease. You can also prune the plants to open them up to better air circulation. Nandina plants send new stems (canes) up from the crown of the plant. Pruning back the canes which are most affected by the disease will remove the disease pathogens and also prompt your plants to produce new canes.
Best wishes with your landscape!
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