There are not many diseases of Azaleas open-air cultivation, mainly including flower rot, bacterial leaf spot, rhizoctonia, brown spot, anthracnose, and root rot.

1. Flower rot disease occurs during the flowering period of Azaleas. At the beginning of the disease, the petals are water-soaked plaques, and gradually expand to a state of soft rot throughout the flowers. The flowers fall off into pathogens, and the sclerotium is very tenacious and has a life span of about 5 years. The control agents include pyrimethamine, thiophanate-methyl, Pu Haiyin, etc., and use them twice according to the instructions, once at the beginning of the flowering period and once at the full-flowering period. (Grey mold disease occurs during the flowering period of greenhouse cultivation: control methods are the same as flower rot).

【From left to right： Early, mid, late stage of flower rot symptoms】

【From left to right： Early, mid, late stage of Grey mold disease】

2. Bacterial spot leaf disease generally occurs after flowering to the growth period of new shoots. The initial infection is needle-like black-brown circular spots. As the spots expand and increase, the leaves fall off. Generally, the plant occurs from bottom to top. When it is windy and rainy, the disease of susceptible varieties spreads quickly, often causing many susceptible leaves in a short period of time. After flowering, you should pay attention to the weather and disease conditions, and control should be done early rather than late. You can use Zhongshengmycin, Kasugamycin, etc. The disease is selective for Azalea varieties, and it is best to choose varieties with high resistance.

【Symptoms of bacterial spot leaf disease】

2. Brown spot disease and anthracnose generally occur from July to September. When brown spot disease is susceptible, irregular black-brown spots appear, and severe symptoms can cause early defoliation. Anthracnose occurs less frequently, and the symptoms are striated. For prevention and control, fungicides such as tebuconazole, propiconazole, thiophanate-methyl, and myclobutanil can be used for rotation control. The susceptible varieties are prevented and controlled once every 10-15 days in the early stage of the disease, and about 3 times a year are required. Varieties with strong disease resistance Azaleas planted in the open field do not need chemical control if they do not have the above diseases or the diseases are relatively light.

【Symptoms of brown spot disease】

【Symptoms of anthracnose】

4. Rhizoctonia and flower rot are the same type of bacteria: Rhizoctonia generally occurs from June to October. The symptoms are a large number of black rotten leaves in a concentrated area, and there are filamentous adhesions at the diseased site, which will endanger new branches. The stems can even cause the entire plant to rot and die. Especially in high humidity or continuous rainy weather, coupled with high planting density, poor ventilation, and heavy dew, this kind of disease is easy to happen. Varieties with small, dense leaves (especially for Rhododendron Indicum) are most susceptible to this disease in shaded conditions. It was found that the diseases were selectively controlled with pyrimethamine, thiophanate-methyl, and Park Haiin.

【Symptom of rhizoctonia】

5. Root rot is mainly caused by a combination of factors such as diverse varieties' tolerance poor air permeability, long-term accumulation of water in the foundation, high pH value, high salinity, and pathogenic bacteria. It generally occurs after the rainy season and encounters high-temperature conditions. Once the disease is found, it cannot be rescued, which needs to be removed immediately together with the root. Selecting varieties with strong disease resistance, improving air permeability, paying attention to drainage, using ferrous sulfate more, and changing soil for container cultivation can reduce the occurrence of this disease. Preventive agents include metalaxyl, oxamid, and ferrous sulfate.

【Symptom of root rot disease】

6. Generally, in the north of Jiangsu Province and in areas with relatively low humidity in spring and summer, diseases such as flower rot, bacterial leaf spot, and Rhizoctonia are not easy to occur due to climate reasons.

In order to protect the environment and reduce environmental pollution, please try to choose azaleas varieties with strong disease resistance for planting!