Mycosis-- orchid anthracnose

Orchid anthracnose [also known as Orchid spot]

Distribution: Worldwide; common throughout southern China.

Pathogens: Collectotrichum gloeosporioides, Collectotrichum cinctum.

Host: Aerides, Cattleya, Coelogyne, Cymbidium, Cypripedium, Dendrobium, Eria, Laelia, Oncidium, Paphiopedilum, Phaius, Phalaenopsis, Pholidota, Vanda, Vanilla, and others.

Symptoms: Water-filled black or brown raised pustules on pedicels, buds, and lower or occasionally upper surfaces of petals and petals. A number of dark brown or light gray areas appear on the leaves, with many black spots, clustered into a number of bands, with horizontal walk or form concentric circles. Lesions are marked by strips of black tissue and are often surrounded by yellow bands. As black lesions develop, the surrounding tissue turns yellow or greyish green and sags. The spots are round or ovate, reddish brown at first, then dark brown or gray. Small clusters of spores or occasional fruiting bodies can be seen on the spots of dried old leaves. Orchids bow and wither or die.

Control: Cut off infected organs and spray with 800 times solution of 50% carbendazim or 1000 times solution of 75% thiophanate-methyl. For example, 65% Zineb 600-800 times solution or 75% Chlorothalonil 800 times solution can be sprayed before disease control, and the effect is good.

Note: Excessive nitrogen fertilizer can easily cause infection of this pathogen. Anthrax is easy to infect orchids, such as spring orchids, cold orchids, etc., mainly in the mildewed season. Vanilla anthracnose is also caused by Glomerella vanillae and Calospora vanilllae, but the symptoms are similar and the control methods are similar. (Chen Xinqi, Ji Zhanhe)