Azaleas belong to the genus Rhododendron. There are two categories of azaleas--deciduous, which are the North American species, and evergreen, which are the Japanese species. Azaleas bear flowers of many hues--white, yellow, pink, red, orange and purple. They are generally disease-resistant flowering plants when supported by the right soil content and environmental conditions. However, azaleas can become prone to disease when healthy conditions are not maintained.
Powdery mildew is an infection caused by Microsphaera penicilata or Erysiphe polygoni, and is characterised by a yellow spots on the leaves. Sometimes the areas become dead spots, or a pronounced fungal growth forms in these areas.
Botryosphaeria canker is caused by Botryosphaeria dothidea, and forms dark-brown, rough areas near breaches in the azalea's bark. Cankers then continue to form along the branch.
Ovulinia Petal Blight
Ovulinia petal blight is a disease that is caused by Ovulinia azalea. It is characterised by spots that form on the azalea flower petals. These light-coloured spots very quickly become larger until it overtakes the entire petal, causing it to deteriorate.
Leaf and Flower Gall
Leaf and flower gall is a disease caused by the fungus Exobasidium vaccinii. It infiltrates the flowers and leaves to germinate more spores. These spores form galls on the surfaces of the flowers and leaves, and then the newly formed spores remain dormant until the next year, when it can reinfect the plant.
Cercospora Leaf Spot
Cercospora leaf spot is caused by Cercospora handelii, a disease that causes brown spots to form on the lower leaves of the azalea plant. The disease causes the infected leaves to fall.