Schlumbergera, commonly referred to as Christmas cactus, derives its common name from its winter bloom period. Each of the six Christmas cactus species produces a different colored bloom, with red being the most common. As with all cacti and succulents, the Christmas cactus is susceptible to disease. Fungal leaf spots, sooty mold, botrytis and basal stem rot are common diseases associated with this plant. The effects of pests are often mistaken for disease, but pests can often be eradicated. In some cases a diseased plant can be treated. In others, the plant cannot be salvaged.
Fungal Leaf Spots
Cut away any infected leaves with a clean razor blade. Unfortunately, the infected leaves cannot be rejuvenated. Fungal leaf spots are typically circular or elliptical in shape and develop along the leaves of the plant. The spots are typically black or gray in color.
Move the plant to a well-ventilated area.
Water the plant at the ground level and only after the soil is allowed to dry completely. Fungal leaf spots develop from water that rests on the leaves and stems for long periods. It is for this reason that you should avoid pouring water directly over Christmas cactus, particularly if the plant is exposed to shade for long periods of time.
Sooty Mold and Botrytis
Remove as much soil from the roots as you reasonably can without damaging the root system.
Repot the plant with new soil specifically formulated for cactus and succulents.
Treat the blackened areas with a systemic fungicide if treating sooty mold and with methylated spirits if treating botrytis.
Move the plant to a well-ventilated area if treating botrytis.
Allow the soil to dry completely between waterings.
Basal Stem Rot
Cut away any leaves not yet infected with a clean razor blade. Unfortunately, a Christmas cactus suffering from basal stem rot cannot be rejuvenated, but healthy leaves can be repotted.
Plant the healthy leaves in new soil specifically formulated for cacti and succulents.
Apply copper sulfate to the healthy cuttings to guard against basal stem rot.
Identify the type of pest attacking the plant. Mealybugs are identified by their white woolly nests and waxy appearance. The bugs are very small and a gray-white color. Spider mites are red in color and feed on the leaves of the plant. They are very hard to see without a magnifying glass. Look for spider webs with small dots. The dots are the spider mites. Whiteflies closely resemble mealybugs, but do not build nests. Whiteflies excrete honeydew, which can lead to sooty mold.
Move the plant to an area where temperatures exceed 70 degrees F for all pest types. It may be necessary to invest in a small greenhouse if temperatures in direct sunlight do not reach at least 70 degrees. Moving the plant to a warmer environment should eliminate the spider mites.
Spray the plant with soapy contact insecticide if treating a plant with mealybugs.
Increase the humidity level if the spider mite infestation is extensive and they survive the warmer temperature.
Spray whiteflies with an insecticidal spray.