There are different types of azalea diseases that gardeners might encounter with these typically hardy shrubs. Most of the diseases are caused by fungus that attacks the foliage, but some azalea diseases also infect the branches and root system. The more common diseases that might occur when growing azalea shrubs include azalea gall, petal blight, mildew, rust, twig blight and root rot.
Azalea gall, also known as leaf gall, is a fungus that typically appears after the shrub has bloomed. The fungus often attacks young foliage, leading to an unattractive plant that cannot produce bountiful blooms. The disfiguring galls can be visually seen, varying from small pea to plum size, and should be removed when noticed. The fungus is spread through the air, so the discarded leaves should be disposed of properly to prevent further contamination.
Petal blight is a rapidly spreading disease also referred to as flower spot. On colored flowers, petal blight will appear as white spots, and on white flowers, the disease appears as brown spots. Environments that have high humidity and rainfall are breeding grounds for the fungus that causes petal blight. Fungicides designed specifically for petal blight are one of the best ways to control the disease.
There are several types of azalea diseases associated with mildew. The more recognized form is powdery mildew. This distinctive problem appears as a white or grayish powdery material that leads to premature leaf dropping, which detracts from the azalea’s overall appearance. Humidity, lack of sunlight and over-watering are common causes of this disease. Like petal blight, powdery mildew can be controlled with the appropriate fungicide.
Of all the azalea diseases, rust is perhaps one of the more troublesome, because the fungus that causes the disease can rapidly reproduce. Rust appears as yellow, circular spots on the leaf’s surface and reddish-orange on the underside of the leaves. The preferred method for controlling rust is removal and disposal of the affected leaves.
Most azalea diseases affect the shrub’s foliage, but twig blight attacks the azalea’s branches. Infected branches or twigs will show signs of deterioration and wilting. The underside of the branch’s bark will have a reddish discoloration that might extend through only a small section of the branch or along the stem’s entirety. Fungicides generally are ineffective for treating twig blight. Removing and discarding the infected twigs is the more effective practice for controlling this disease.
Root rot is caused by a fungus that can travel through the soil via water movement. The fungus causes the azalea’s roots to brown, and it travels through the shrub, leading to droopy and discolored foliage. When infected with this disease, the roots will become brittle to the touch and are easily breakable. Azalea root rot is incurable. Gardeners should remove azaleas that have root rot from the ground and dispose of properly to prevent the spread of the disease to other plants.