Powdery mildew is caused by the fungus Microsphaera vaccinii, which only infects blueberries. This disease rarely causes serious harm to blueberry plants. Powdery white fungal growth can be seen on infected leaves in late summer. In some cases, fungal growth is limited to the lower surface of the leaf and yellow or red discoloration can be seen on the upper surface of the leaf. It is important to closely examine discolored leaves for fungal growth on the lower leaf surface so as not to confuse powdery mildew infection with viral disease. No control is necessary. Choosing a site in full sun with good air movement will help to reduce problems with powdery mildew. Space plants to provide good air movement between plants.