An orchid plant is more prone to disease than many other types of plants and must be treated immediately when signs of disease appear. For indoor growers of orchid plants it is important to try to treat the plant outdoors if possible and bring it back once the problem is corrected. A common disease for orchid plants is bacterial root rot, which is identified when the lower leaves begin to shrivel. This condition often is caused by over-watering. When root rot appears, you must repot the plant and remove all of the bad roots without damaging the plant.
Take your plant out of the pot once you notice that lower leaves are dying. If the root is soft and dark, the orchid most likely has root rot and the diseased roots must be removed.
Wear latex gloves when handling the diseased roots, and slightly tug on the root. If it's soft from root rot, more than half of it should simply snap off. Dispose of the diseased roots that come off when you pull.
Use a sterile knife or razor blade to cut the rest of the diseased roots off. Cut off the entire root by slicing at a 45-degree angle and make sure not to cut off any healthy parts of the plant.
Remove all the dead leaves from the bottom of the orchid and make sure to scrape off any soil. Dispose of all the rest of the soil in the pot quickly before transferring your orchid plant to a new pot.
Straighten the plant so it is centered and replant in a smaller pot. Add slightly moistened bark to the roots until it reaches the level of the leaves. Don't water for two or three days, and reduce watering.