Below are some of the characteristics of:
Fungus Diseases
Black rot of leaves and pseudobulbs: Dark spots appear at the base of the leaves and then turn black. This attack may be caused by poor root aeration, excessive humidity and too low temperature.
Solution: If the plant is totally covered by the diseases the only solution is to destroy the plant. However, if it was only a partially affected, remove the diseased portion of the leaves with a sharp sterile razor blade and treat the whole plant with a solution of systemic fungicide.
Grey Mold: The outer flower has small brown dots or spots i.e. "Botrytis". This mainly caused by high humidity and a low temperature...which in turn causes condensation on the flower itself.
Solution: Raise the overall temp to 60 F and lower the humidity. The affected flowers can not be saved. Basal and Root Rots: Also known as Pythium and Phytophthora. These cause scattered spopts to appear on the leaves of the plant to the pseudobulbs. The back-bulbs often turn black first. The cause of this rot is because the potting medium is too wet.
Solution: Cut off the affected back-bulbs from the roots with a sterile razor blade. Soak plant in fungicide and replant into fresh potting medium. Adjust your watering so it is less frequent.