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Symptom Identification and Control Methods for Oleander Leaf Spot

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Symptoms: The spots occur at the edges or center of the leaves, semicircular or circular in shape; when several spots merge, they form a wavy pattern. They appear on both the upper and lower surfaces, with the upper surface slightly darker than the lower, and the spots are grayish-white or grayish-brown. In the later stage, a black powdery mold layer appears on the diseased parts, generally on old leaves. Pathogen and disease status: The pathogen is a fungus of the genus Alternaria (Alternaria sp.). Spores spread by wind and rain, and excessive rain easily triggers this disease. The disease occurs more often on old leaves, lower leaves, and tiller shoots sprouting from the roots. Control methods: 1. Strengthen

Symptoms: The spots occur at the edges or center of the leaves, semicircular or circular in shape; when several spots merge, they form a wavy pattern. They appear on both the upper and lower surfaces, with the upper surface slightly darker than the lower, and the spots are grayish-white or grayish-brown. In the later stage, a black powdery mold layer appears on the diseased parts, generally on old leaves.

Pathogen and disease status: The pathogen is a fungus of the genus Alternaria (Alternaria sp.). Spores spread by wind and rain, and excessive rain easily triggers this disease. The disease occurs more often on old leaves, lower leaves, and tiller shoots sprouting from the roots.

Control methods:

1. Strengthen management and improve ventilation and light penetration for the plants. Apply more phosphorus and potassium fertilizer to strengthen the tree vigor.

2. Spray 75% chlorothalonil at 800 times dilution for control.

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