How to diagnose orchid diseases? Find the root cause from leaf characteristics

Judging the root cause of a disease from the characteristics of orchid leaves

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1. Orchid leaves turn yellow but growth is normal: this is too much light. 2. Orchid leaves turn yellow and new shoots are small: excessive light, lack of nitrogen fertilizer and necessary humidity. 3. Old leaves yellow and fall off: normal aging or caused by repotting. 4. Old leaves yellow and fall off rapidly: watering too much and too often, improper potting when repotting. 5. Tips of new leaves are scorched: excessive fertilizing, unclean potting material. 6. Both new leaves and old plants have scorched black tips: excessive damp heat inside the pot, with rotted roots among the root system. 7. New shoots emerge from the soil and then stop growing: there are rotted roots or unclean matter beside the new shoots; open up the growing medium around the new shoots and remove the unclean matter and growth will resume. 8. Orchid leaves have scorched spots with no yellow rim: sunburn spots. 9. Leaf tips appear scalded and shriveled: the water temperature for watering is too high; the air temperature is too high when watering; exposure to sudden rain showers during high summer temperatures, etc. 10. New shoots rot at the core: water poured into the shoot core cannot evaporate or be absorbed, and unclean growing medium in the pot causes leaf rot disease, etc. 11. Orchid leaves have spots with water-soaked rims: excessive humidity, pot moisture combined with air humidity causing suffocation, accompanied by leaf rot fungi. Poor ventilation and air movement. 12. Leaves have yellow-brown spots: caused by the root area being overheated. 13. Orchid leaves have irregular yellow spots, with the leaf mesophyll tissue necrotic and sunken: caused by viral disease, also known as Baras. 14. Leaves have small yellow spots: caused by scale insects. 15. Orchid leaves show purple-black color while the underside remains green: caused by low-temperature frost. It can also occur from phosphorus deficiency. 16. Leaves dehydrated, pseudobulbs wrinkled and shrunken: caused by long-term excessive dryness and dehydration in the pot.

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Orchids are ornamental plants of the family Orchidaceae, and the common diseases mainly include anthracnose and leaf spot disease. 1, Orchid anthracnose: mainly harms the leaves; in the early stage of the disease, dark brown lesions appear on the leaves, surrounded by a faded green halo. After the lesions expand, they become elliptical or elongated. The margins are dark brown, the interior is yellow-brown, and the lesions are slightly raised. In the later stage, black granular bodies appear on the lesions; under moist conditions the black granular bodies exude pink gelatinous matter, namely the pathogen's acervuli and conidial masses. Anthracnose occurs over a long period, with the most severe incidence in July and August. Control: ① Pay attention to ventilation and light penetration. ② Fertilize reasonably to improve disease resistance; during the growing period, control the application of nitrogen fertilizer and apply appropriately more phosphorus and potassium fertilizer. ③ In the early stage of the disease, spray 50% carbendazim or 70% thiophanate-methyl wettable powder at 500-800 times dilution. 2, Orchid leaf spot disease: it is a fungal disease that harms the leaves and can occur throughout the entire growing period. High temperature and high humidity, damage by scale insects, and poor ventilation all make leaf spot disease likely to occur. In the early stage of leaf spot disease, the lesions are brown; after expanding, the lesions become long elliptical to elongated streaks, with red-brown margins and a gray-brown interior. In the later stage, black granular bodies are scattered on the lesions. Control: ① Improve ventilation conditions and eliminate pests. ② In the early stage of the disease, spray 50% tebuconazole? No. 50% Tuzet at 1000 times dilution or 65% zineb at 800 times dilution for control.