Symptoms and Control Methods of Azalea Gall Disease

Symptoms: It can harm the young branches, shoot tips and leaves of azaleas. After the leaves are affected, the edges or the entire leaf become swollen and thickened, forming tumor-like or hemispherical fleshy galls. After young branches are affected, they also swell and thicken into fleshy galls, affecting new shoot growth. After flowers are affected, a white powdery mold layer, namely the fungal hymenium, grows on the petal surface or in depressions. In the later stage, the galls turn brown, wither and fall off.

Pathogen and current disease situation:

Pathogen: Exobasidium hemisphaericum Shirai, Basidiomycota, Hymenomycetes, Exobasidiales.

Disease pattern: The mycelium overwinters on plant residues. In the following year, when the daily average temperature rises to about 10 degrees Celsius and the relative humidity reaches above 80%, it begins to produce basidiospores. The basidiospores spread with wind and rain, infecting young leaves, tender shoots or petals. After half a month, the diseased parts begin to discolor and wither, and after about 25 days the diseased leaves completely wither and fall off. Late March to early and mid-April is the first peak period of disease occurrence, and late September is the second peak period.

Control methods:

1. Select disease-resistant varieties.

2. In spring and autumn, remove and destroy diseased tissues, and in winter promptly clear and centrally destroy plant residues in the azalea garden.

3. In early March and mid-September, spray 15% fenarimol wettable powder at 1500 times dilution, or 80% zineb wettable powder at 800 times dilution, or 50% Tuzet wettable powder at 500 times dilution.