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Pathogen and pathogenesis: The pathogen is Alternaria sp. Spores spread by wind and rain, excessive rainfall caused the disease, the old leaves, lower leaves and roots litter germination.
Control measures:
1. Strengthen management and enhance plant ventilation and light transmission. Apply more phosphorus and potassium fertilizers to increase tree vigor.
2, spray 75% chlorothalonil 800 times for control.
Oleander black spot
Symptoms: The lesions occur on the edges or middle of the leaves. They are semi-circular or round. When several lesions are connected, they form a corrugated shape. Both sides are positive and negative. The front is slightly darker than the back, and the lesions are off-white or gray-brown. . Later in the disease, there is a layer of black powdery mildew that usually occurs on old leaves.