Which disease specifically affects azaleas?

Gall specifically affects azaleas and is caused by tiny insects known as gall-forming pests, such as the azalea lace bug or certain types of leaf galls. The presence of galls can lead to distorted growth on the leaves, stems, or flowers, making it a significant concern for the health and appearance of azaleas. Galls are abnormal growths that can interfere with the plant's ability to photosynthesize properly, leading to overall decline if not managed.

Root rot can affect various plants, including azaleas, but it is not specific to them, as it primarily results from poor drainage and overwatering conditions. Powdery mildew is a widespread fungal disease impacting many ornamental plants, not limited to azaleas alone. Leaf curl can affect various types of plants, including some fruit trees and ornamentals, but it is not a disease specifically associated with azaleas. Therefore, gall stands out as the correct answer due to its specific link to azaleas and the unique growth structures it causes.