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How to treat oleander leaf spot? Detailed methods for disease control in medicinal plants

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Oleander, scientific name Nerium indicum Mill., is a woody plant of the family Apocynaceae. Its leaves and flowers are used as medicine; it is toxic. It has the effects of strengthening the heart and promoting diuresis, eliminating phlegm, and killing insects. It is distributed in most provinces and regions across the country. Symptoms mainly affect the leaves. At first, small purplish-red spots appear at the leaf tip or leaf margin, and after expanding they form circular, semicircular to irregular brown lesions. The lesions have concentric rings. In the later stage the center fades to white, and the red-brown margin is relatively wide. When humidity is high, a grayish-brown mold layer can grow on both sides of the lesions, namely the pathogen's conidiophores and conidia. The disease

Oleander, scientific name Nerium indicum Mill., is a woody plant of the family Apocynaceae. Its leaves and flowers are used as medicine; it is toxic. It has the effects of strengthening the heart and promoting diuresis, eliminating phlegm, and killing insects. It is distributed in most provinces and regions across the country.

The symptoms mainly affect the leaves. At first, small purplish-red spots appear at the leaf tip or leaf margin, and after expanding they form circular, semicircular to irregular brown lesions. The lesions have concentric rings. In the later stage the center fades to white, and the red-brown margin is relatively wide. When humidity is high, a grayish-brown mold layer can grow on both sides of the lesions, namely the pathogen's conidiophores and conidia.

Pathogen Cercospora neriella Sacc., called European oleander Cercospora, is a fungus of the subphylum Deuteromycotina. The stroma is dark brown, 25-125 μm in size. The conidiophores are light in color, uneven in thickness, gathered into bundles, with 0-3 septa, unbranched, with small spore scars at the apex, 5-35 x 3-5 (μm) in size. The conidia are cylindrical, with 1-5 septa, 15-50 x 3-5 (μm) in size. In addition, C. nerii-indici Yaman, called oleander Cercospora, is also a pathogen of this disease.

Transmission routes and disease conditions: The pathogen overwinters as mycelium on diseased leaves or remains on the soil surface with fallen leaves. In the following spring it produces conidia, which spread to oleander through wind and rain. The germinating spores invade through stomata or wounds, causing disease. It occurs from March to July. The disease is more severe when seedlings are planted too densely or are weak and slender.

Control methods (1) Strengthen seedling management, avoid planting too densely, and remove diseased leaves and burn them in a centralized manner. (2) At the early stage of disease, spray 50% benomyl wettable powder at 1000 times dilution, or 25% carbendazim wettable powder at 600 times dilution, or 36% thiophanate-methyl suspension concentrate at 500 times dilution.

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