Some of the more common orchid plant diseases include varying degrees of "rot". There are different types and include Bacterial Leaf Rot, Bacterial Root Rot and Crown Rot.
Leaf rot, is another one of orchid plant diseases which appears as a slight discoloration of the leaf. It is in noted as a spot on the leaf. It is not that the entire leaf is a lighter or darker green color. If you catch it late you will note that the spot has gotten larger and has irregular borders. The infected part eventually turns gray. and becomes soft in texture. The remedy is to cut the leaf back to the healthy tissue using generally a clean and if possible a sterile instrument or blade. I like to use a new single edge razor blade and discard the razor blade after it has been in contact with the diseased area.Treat the good edge of the leaf with a bactericidal solution. Or it is possible to sprinkle the spice cinnamon. Then make sure the plant is in a place of good good air circulation.
Another orchid plant disease is Crown Rot which is the same as leaf rot but in a larger area and has greater ramification. It takes the uppermost leaf or leaves thus the name "crown". The remedy is to remove the uppermost leaf or leaves that will be soft usually at the attachment to the plant stem. It is important to remove all the diseased area including digging into the crown of the plant with a sterile knife or blade edge. Once again treat the open area with anti-bacterial solution. Or again I like to sprinkle the area with cinnamon.
Bacterial Root Rot shows itself as some shriveling of the lower leaves. This is a common orchid plant disease. Over watering can cause this problem. The treatment here is different and includes re-potting. When you take the plant out of the pot you will notice that the roots are dark and soft. The remedy includes removing the bad roots and the media around them. Because they are soft when you pull the roots to remove they will break off easily. Use a smaller pot this time and re-plant. Do not water for several days and then water less frequently than you have.
Leaf Burn occurs when the plant is over exposed to sunlight. You will see some gray-white areas on the leaf. These will usually get better but just keep an eye on it for these spots may get infected.
Bud Blast is the withering and falling off of buds. This can occur either with the bud in the sheath or when they emerge as buds. The cause is usually some sudden drastic changes that the plant undergoes. This may be from a sudden temperature change or light change. It may be also caused by allowing the plant to dry out excessively. It is important to not put plants in front of the heater vents when we bring them into our houses.
Black Spot / Black Leaf. This is common in both the Paphiopedilum and the Oncidium plants. This is caused by either too much fertilizer or not enough fresh water. They are unsightly spots on the leaf which as the name implies is black in color. It may be on the body of the leaf or on the tip of the leaf. Also, check on the air circulation in this area of the orchid plant.
These tend to be the most common orchid plant diseases. Be aware of them and you probably won't get them!