Anthracnose of Orchid (2)

Orchid anthracnose is one of the most important diseases of orchids.

[Pathogen] Colletotrichum orchidaerum and C.orchidaerumf. cymbidii Allesch belong to the genus Echinosporium and subphylum Fungi.

[Symptoms] At the beginning of the disease, there are yellowish brown slightly depressed small spots on the leaves, gradually expanding into dark brown round or oval spots. Leaf tip lesions can extend downward causing leaf segment die-off; leaf base lesions can cause rapid die-off of whole leaves. In the later stage, there are small black spots in the middle of the disease spots, which are merisporal discs of the pathogen.

Pathogen overwinters on diseased plant residues and pseudobulbs; conidia are produced in the following spring to invade from wounds or directly invade from young leaves. The optimum temperature for conidia germination was 22-28℃. Free water was favorable for conidia germination. The disease can occur from March to November every year.

[Epidemic characteristics] high humidity or musty rain season disease is heavier; plants are too dense, poor ventilation or high environmental humidity, water in the flower bed is also easy to cause disease development. There were significant differences in resistance among different orchid varieties.

[Control measures] A. In the growing season, timely remove the diseased spots on the leaves or remove the diseased plant residues. B. Reduce environmental humidity, keep ventilation and light transmission; watering should be done by drip irrigation or along the edge of the basin, avoid watering. C. At the initial stage of disease occurrence, 70% thiophanate-methyl WP 800 times solution or 50% carbendazim WP 500 times solution or 50% captan 500 times solution can be sprayed for control, spraying once every 10 days or so, and the spraying frequency depends on the development of the disease.