Schlumbergera bridgesii, commonly referred to as Christmas cactus, derives its common name from its winter bloom period. Hardy in U.S. Department of Agriculture plant hardiness zones 10 through 12, the three types of holiday cacti have different bloom times, dependent on hours of darkness and temperatures. They produce a variety of exotic, colored flowers, with red and pink being the most common. As with all cacti and succulents, the Christmas cactus is susceptible to disease and pests.
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Fungal leaf spots, sooty mold, botrytis and basal stem rot are common diseases associated with these tropical cacti. The effects of pests are often mistaken for disease, but pests can often be eradicated. In some cases a diseased plant can be treated, while in others, the plant cannot be salvaged.
Fungal Leaf Spots
Step 1: Remove Infected Leaf Segments
Cut away any infected leaves with a sterilized razor blade or garden knife. Dip the blades in rubbing alcohol or Lysol and allow to air dry. Unfortunately, the infected leave segments cannot be rejuvenated. Fungal leaf spots are typically black or gray, circular or elliptical spots that develop along the leaves of the plant.
Step 2: Provide Air Circulation
Move the plant to a well-ventilated area. A fan in the room helps increase air movement around and through the plant.
Step 3: Keep the Leaf Segments Dry
Water the plant at the ground level and only after the soil is allowed to dry to a depth of 1 to 2 inches. 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
Step 1: Remove Soil From the Roots
Remove the Christmas cactus from the flower pot. Carefully brush away as much soil from the roots as you reasonably can without damaging the root system.
Step 2: Repot in Fresh Potting Soil
Repot the plant with new soil specifically formulated for cactus and succulents. Alternately, mix 2 parts peat moss or compost and 1 part each of potting soil and coarse sand, perlite or vermiculite.
Step 3: Treat With Fungicide
Treat the blackened areas with a systemic fungicide if treating sooty mold and with methylated spirits if treating botrytis. Put on safety gear, including goggles, gloves and a dust mask when working with fungicides, insecticides and compost.
Step 4: Provide Additional Air Circulation
Move the plant to a well-ventilated area if treating botrytis. If the weather is warm, a vacation outside in the garden can provide more air circulation. Inside, a ceiling or oscillating fan can keep the air moving in the room.
Step 5: Cut Down on Watering
Allow the soil to dry to a depth of 1 to 2 inches between waterings. Don't allow the plant to go completely dry; Christmas cacti are tropicals and need an evenly moist, but not waterlogged, soil to thrive.
Basal Stem Rot
Step 1: Save Uninfected Leaf Segments
Cut away any leaf segments not yet infected with a razor blade or knife sterilized by dipping the blades in rubbing alcohol. Unfortunately, a Christmas cactus suffering from basal stem rot cannot be rejuvenated, but healthy leaf segments can be repotted.
Step 2: Dry the Cuttings
Put the leaf segments aside for day or two, until the cut ends develop callouses. Swirl in rooting compound, if desired, to encourage quick rooting.
Step 3: Plant the Healthy Leaf Segments
Plant the healthy leaf segments in new soil specifically formulated for cacti and succulents. Keep the mix slightly moist and cover the pot and cutting with a plastic bag to keep the humidity high while rooting the new plants.
Step 4: Treat With Copper Sulfate
Put on gloves, safety glasses and a dust mask. first Apply copper sulfate to the healthy cuttings to guard against basal stem rot.
Pests and the Christmas Cactus
Step 1: Identify the Pest
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.
Step 2: Move to a Warm Location
Move the plant to an area where temperatures exceed 70 degrees Fahrenheit 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.
Step 3: Treat With Insecticide
Spray the plant with soapy contact insecticide if treating a plant with mealybugs. Whiteflies may require treatment with an insecticidal spray.
Step 4: Increase the Humidity
Increase the humidity level if the spider mite infestation is extensive. Warm temperatures may not discourage these tiny pests. A cool steam vaporizer adds moisture to the air.
John Stevens has been a writer for various websites since 2008. He holds an Associate of Science in administration of justice from Riverside Community College, a Bachelor of Arts in criminal justice from California State University, San Bernardino, and a Juris Doctor from Whittier Law School. Stevens is a lawyer and licensed real-estate broker.