Of all the diseases that can infect orchids, virus infections are the most dreaded as there is virtually no cure. Symptoms include circular or diamond-shaped brown spots and blotches on the leaves and color streaking in flowers. However: this does not mean that every orchid with brown-spotted leaves is virused. Brown spots can occur because of sunburn, the sudden onset of bright light after a dark winter, or a fungus infection. Since many orchids retain their leaves for several years, foliage is bound to develop markings and spots as the leaf ages. If you do suspect a virus, you may pay to have your plant tested at one of the many labs set up for this purpose. Check the "LINKS" page for more information. The best "cure" for a viral infection is prevention: keep your growing area clean, and always used sterilized implements if you're going to be cutting into your plant. This includes cutting off old flower spikes that haven't completely browned out yet.

Brown rot is a bacterial infection that causes wet, brown spots to appear on leaves and pseudobulbs. It can be caused by temperatures that are too low and humidity that is too high, or by a slug that has begun to graze. These infections can spread quickly so they must be dealt with as soon as they're noticed. Using a sharp, sterilized knife or single-edged razor blade, cut away the affected area and dust the wound with either sulphur powder, a solution of Physan and water, or some other antibacterial agent designed for use on Ornamentals. If allowed to spread, these infections can kill your plant in a matter of days.

Black rot and crown rot are fungal infections which usually result from overwatering or watering in the evening so that water is left standing in the crown of the plant. Spray the plant with an appropriate fungicide for use with Ornamentals. Unfortunately, if crown rot infects a Phalaenopsis, the plant, with no other active area of growth except the crown, will die. All fungal infections can be avoided by proper culture: do not overwater, water only in the mornings so that your plant has a chance to dry off before nightfall, and provide plenty of air circulation around your plants. If you notice a puddle of water standing in the crown or active growing center of your orchid, soak it up with a paper towel.

This list is by no means exhaustive. Much research has been done in the area of orchid disease; for further information, consult the "LINKS" page.