Considering the fact that fungi comprises the largest kingdom of organisms on this planet, with a conservative estimate of up to 100,000 species and the possibility of twice as many, research in this field must be an astronomical task.
Nevertheless, research has been carried out to some extent on the most common fungi found in orchids and cymbidiums in particular. However, identification of the various species is not easy and only specialized experts with help of electron microscopes are capable of delivering the right information.
The reason for this the habit of some fungi to form different strains, changing in shape and size but also creating different patterns of destruction not only from one species to another but also from one plant to the next of the same kind. This can make field identification not only difficult but almost impossible. The matter is compounded further when more than one fungus is present.
The pathogenic fungi we are dealing with could be simply grouped into airborne or soil borne types. The spores of the former are carried by wind and thermal currents (sometimes long distances) whilst the latter more commonly relies on water transportation (rain, watering, splashing). Both of them need water or high humidity for the release of the spores and the same for germination.
Airborne fungi are more common and widespread, causing damage to leaves and flowers but rarely kill a Cymbidium unless the damage is extreme. Their presence can be detected much earlier and plants treated sooner to prevent widespread damage. Most of the fungi we are dealing with (including the soil borne types) are entering the host plants through open wounds, damaged tissue (e.g. sunburn), stomata or plants under stress, although some are capable of piercing directly into healthy tissue.
Soilborne fungi are very common in soils or potting mixes. Normally they live in harmony with the plants but once conditions become ideal, like warm weather or high humidity, they will attack. By the time it becomes evident that something is wrong with a plant, finding bunches of yellow leaves, shrunken and wobbly bulbs it usually will be too late to save it.
‘Prevention is better than cure’. Good culture is a starting point. Unfortunately for many ‘backyarders’, when space, time and money is involved, it remains a dream.
Give some space between plants to allow for better air circulation, this allows leaves to dry quicker.
Don’t let plants deteriorate too far; repot every 3 to 4 years; divide plant in case of too many back-bulbs than green bulbs; use fresh potting mix.
Water plants in the morning or allow plenty of time for leaves to dry before nightfall.
Fungi spore needs water or high humidity to start germinating. It also needs the same for survival until either an open wound or stomata is found, to allow for entrance into the host. Keeping the plants dry certainly helps, using preventative fungicides will improve your chances every better.