Mycosis-- black rot of orchid

Orchid black rot (Orchid blak rot), also known as crown rot (Crown rot), stunting disease (Damping off) or heart rot (Heart rot)]

Distribution: worldwide; common in Asia.

Pathogens: Phytophthora Palm (Phytophthora palmivora) and Phytophthora infestans (Phytophthora cactorum).

Hosts: Cattleya, Coelogyne, Cymbidium, Dendrobium, Laelia, Oncidium, Paphiopedilum, Phaius, Phalaenopsis, Rhynchostylis, Vanda, Vanilla and so on.

Symptoms: small brown wet spots with yellow edges appear in the early stage of infection. Irregular damp spots are often seen on the lower surface of the leaves, and then gradually expand. The older and larger lesions turn dark brown or black in the center, ooze water during extrusion, and the old spots become dry and black. The infected leaves turn yellow, wither and fall off, the base near the leaves fade obviously, and the false bulbs become black by infection. The growing points of infected plants fall off easily. In extremely humid conditions, infection can also occur at the tip of the seedling. If you infect the flowers, there will also be light brown (darker central color) wet spots. But the symptoms are not the same in different species and different cultivation conditions. Sometimes the buds are infected first, causing the ungrown leaves to fall off; others first infect the roots and rhizomes, and then extend upward to the base of the pseudobulbs and leaves. The disease eventually led to the death of the whole plant.

Prevention and treatment: remove the infected site or organ, burn it or bury it deeply. It can be sprayed with copper-containing fungicides, such as 0.1% 0.2% cupric sulfate solution, or with 50% carbendan wettable powder 400 × 500 times, 80% aluminum ethyl phosphate wettable powder 400% 600 times, 25% Ruidu (metalaxyl) wettable powder or 1% Bordeaux solution. It is an effective measure to prevent this disease by spraying 50% Fumishuang 100: 150 times liquid frequently. In addition, keeping ventilation and avoiding dampness can prevent the spread of the disease.

Note: the disease is easy to pass through contaminated culture soil. The spread of water, especially in the environment of high temperature and humidity, is especially fast. The pathogen of another black rot is Ultimate Pythium (Pythium ultimum). The symptoms are similar. The pseudo-bulb hardens at first, then dries up, and can spread to the root. The methods of prevention and control are also similar. (Chen Xinqi, Ji Zhanhe)