Azalea Bush Diseases

Environmental Disease

• Phomopsis dieback is a fungal disease caused by the infection of Phomopsis fungi combined with environmental conditions. This disease appears when a cold winter is followed by a dry summer. Stressed azaleas that are not cold hardy produce wilting and dying branches. When the bark is pealed back on infected limbs, the wood looks reddish-brown and discolored.

Flower Disease

• Petal blight is caused by the fungus Ovulinia azalea and damages the blooms. It occurs when the weather is wet and warm. Small white or rust-colored spots appear on the petals, then spread into large brown blotches. The flowers turn to a tan-colored slimy mass that dries out and sticks to the branches.

Leaf Disease

• Leaf gall is a common in most evergreen azaleas. The fungus Exobasidium vaccinii attacks when the weather is cool and humid in the spring. Azaleas, especially those planted in the shade; develop thick, bladder-shaped, light-green or pink growths. Later, white powder coats the galls as the fungus releases its spores. The infected leaves turn brown and fall to the ground.

Root Disease

• Phytophthora root rot is a disease caused by fungi Phytophthora cinnamoni, P. parasitica and P. citricola. These fungi attack azaleas planted in waterlogged soils. Warm soil temperatures, over-watering, heavy rains and planting too deeply are causes. The infected roots turn a reddish-brown color and break easily. Above ground, the leaves turn yellow and growth slows. In severe cases, plant death occurs within a couple of days.

Soil Deficiency

• Iron chlorosis is an iron deficiency in azalea bushes. The key to preventing this disease is to plant azaleas in acidic soil, which readily releases iron from the soil to the plants. Planting in alkaline soil, which locks the iron in the soil, is a major cause of iron chlorosis. This disease appears as yellowing of new leaves. The webbing between the veins in the leaves turns light green or yellow while the veins remain a darker green.