Detailed Explanation of the Symptoms, Development Patterns and Control Methods of Orchid Leaf Spot Disease

Orchids are one of the varieties that people relatively like to grow. Cultivating orchids at home brings a delicate fragrance and elegance, cultivates the mind and character, and combines work with rest. Leaf spot disease is one of the orchid diseases.

I. Symptoms: When Cymbidium goeringii (spring orchid) is infected, small brownish-black nearly circular or oblong spots first appear on the leaves, then gradually expand into irregular long strip-shaped lesions. The boundary between diseased and healthy tissue is obvious, the lesion is black around the edge and grayish-white in the middle. Later, black small granules, namely the pathogen's pycnidia, are produced on the lesions on the upper leaf surface.

II. Development patterns: The pathogen overwinters on diseased leaves as pycnidia, and the following year produces conidia that spread through wind and rain to cause primary infection. When the temperature is 25-27°C, the disease is prone to occur after rain, and the lesions sometimes perforate.

III. Control methods: (1) Care carefully, pay attention to improving the cultivation conditions of orchids so that they have ventilation and light, and change watering to after the sun comes out in the morning. (2) In the early stage of the disease, spray 50% carbendazim wettable powder at 500 times dilution, or 50% thiophanate-methyl wettable powder at 800 times dilution, or 37% difenoconazole water-dispersible granules at 3000 times dilution.