There are basically two fungal species that cause most of the diseases for orchids. They are cercospora and anthracnose – neither normally kills the plant. They can be found on stressed plants and are more prevalent in moist conditions where air circulation is minimal. The signs are spotting on the pseudo-bulbs and leaves.
Specifically, cercospora symptoms tend to be small yellow spots appearing on the undersurface of leaves. Gradually growing in size, then turning black, the leaf eventually dies. The anthracnose symptoms are sunken, irregular brow discoloration on the plant tissue.
Fungal infections of orchid plants can be prevented by a strict hygiene routine. Quickly remove the dead or dying leaves and infected flowers. Ensure there is good air circulation around the orchid plant and that the temperature and humidity does not get too high. If the orchid plant is already infected with fungi, spray with fungicide with a wetting agent included, at regular intervals. Fungicides that can be used on orchids are benlate, thiram, mancozeb, zineb and caftan.
Most diseases are caused by fungal spores that tend to become a problem – more often during the wet weather season. Diseases can be prevented by utilizing proper cultural practices such as irrigation and humidity management, plant and soil nutrition, pruning, and proper spacing.
When there is inadequate circulation of air, poor water drainage, exorbitant irrigation, and too much dampness due to rainfall, the fungi can become a problem. Organically, the solution is to use copper and sulfur products – result: spores are prevented from growing because the plant has been coated with the appropriate physical barrier.
Fungi are unable to produce nutrients on their own and in order to survive must derive their food from other organisms.
In conclusion, I must admit that growing orchids is in itself not very difficult. After all most kind of orchids survive in the wild, where Mother Nature takes care of them and human hands are not ever needed.
Esther Smith, author
It would seem then that fungus problems with orchids can be avoided with some proper cultural practices regarding irrigation, humidity, plant and soil nutrition, pruning, and proper spacing.
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