Identification and Control Methods for Major Orchid Diseases

II. Soft rot mostly occurs from April to May. As rainwater carrying bacteria enters the young growth center, water-soaked small spots appear, turning from brownish-yellow to black, until the plant becomes foul-smelling and dies. Once it occurs, promptly move the plant to a ventilated place with less moisture, use medicated cotton to absorb the water from the growth center, and spray with 1% Bordeaux mixture or 500-fold diluted chlorothalonil solution, once every 10 to 15 days, for several consecutive applications.

III. Root rot mostly occurs under high temperature and high humidity. When the potting soil becomes waterlogged, the soil becomes compacted, acidity is high, or fertilizer is applied too concentrated, Fusarium opportunistically invades the roots, causing them to gradually rot, and the plant dies because it cannot absorb nutrients. If detected early, repot promptly, discard all the growing medium, cut off the rotten roots and withered leaves, immerse the entire orchid plant in a 0.1% potassium permanganate solution for about 15 minutes, remove it, wash it clean and let it dry, then use "root promoter" diluted 3000-fold with clean water, soak the orchid plant thoroughly for 30 minutes, let it dry, replant it in fresh growing medium, and place it in a ventilated spot.

IV. Southern blight: During hot and humid seasons, the pathogen's mycelium first invades from the pseudobulbs or the base, then harms the roots. After the disease occurs, the leaves gradually turn yellow and dry out from bottom to top, with white silky mycelial strands winding around the surface, slowly spreading to the whole plant. Any orchid root infected with this disease will become hollow in the middle, leaving only fibrous tissue, showing a dry-death phenomenon of broken leaves and broken roots. To prevent southern blight, use clean and sterilized growing medium before planting, and do not apply overly concentrated organic fertilizer. Soak the diseased plant in 600-fold diluted carbendazim solution for 20 minutes, then wash it clean with water and let it dry, then soak it thoroughly in "root promoter" diluted 3000-fold with clean water for 20 minutes, replant it, and place it in a separate location, isolated from healthy orchids to prevent transmission.

V. Sunscald: In places lacking shade, orchids exposed to intense summer sunlight suffer damage to some of the chlorophyll within the leaf tissue, which then becomes necrotic and is subsequently invaded by pathogens, causing lesions. The symptoms mostly appear as brown or black spots. Prevention and control methods focus on strengthening shade facilities, especially preventing exposure to intense midday sunlight.

VI. Yellowing orchid leaves or withered leaf tips are not necessarily caused by pathogens; most are physiological phenomena resulting from poor cultivation and management. This requires attention to improving water and fertilizer conditions, regulating ambient temperature and humidity, and frequent ventilation to resolve.