How To Treat Christmas Cactus Disease (4 Methods)

Most tropical cactus plants sold during the winter holidays as "Christmas" cactus actually are "Thanksgiving" cactus plants (​Schlumberga truncata​). But "true" Christmas cactus plants (​Schlumbergera​ x ​buckleyi​) are susceptible to the same diseases as Thanksgiving cactus and Easter cactus (​Schlumbergera gaertneri​).

All of these holiday cacti are perennials only in the warm climates of U.S. Department of Agriculture plant hardiness zones 10 through 12, and they 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.

Fungal leaf spots, sooty mold, botrytis, and basal rot stem are common diseases associated with these tropical cacti. The effects of pests are sometimes 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 are typically black or gray, circular or elliptical spots that develop along the leaves of the plant. Here's how to remove them:

1. Remove Infected Leaf Segments

Cut away any infected leaves with a sanitized razor blade or garden knife. Dip the blades in rubbing alcohol, or wipe them with an alcohol-soaked cloth. Unfortunately, the infected leaf segments cannot be rejuvenated.

Move the plant to a well-ventilated area. A fan in the room helps increase air movement around and through the plant.

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 are two types of fungi that can harm your plant. Here's how to eliminate them effectively:

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.

Repot the plant with new potting mix specifically formulated for cacti and succulents. Alternately, mix 2 parts peat moss or compost and 1 part each of potting soil and coarse sand, perlite or vermiculite.

Treat the blackened areas with a systemic fungicide if treating sooty mold and with a topical fungicide if treating botrytis. Use a fungicide that's safe for use on holiday cactus. Put on safety gear, including goggles, gloves and a dust mask when working with fungicides, insecticides and compost, and follow all label directions.

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.

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 grow best on evenly moist, but not waterlogged, soil.

Basal rot stem is a decaying of the root system. In order to help your Christmas cactus survive, you have to eliminate the basal rot stem entirely.

1. Save Uninfected Leaf Segments

Cut away any leaf segments not yet infected with a razor blade or knife sanitized by dipping the blades in rubbing alcohol. Unfortunately, a Christmas cactus suffering from basal rot stem cannot be rejuvenated, but healthy leaf segments can be rooted and repotted.

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.

Plant the healthy leaf segments in new potting mix 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.

Like any other plant, Christmas cacti have common pests that afflict them. Here's how to eliminate them:

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 even smaller. They're red in color and feed on the leaves of the plant. They are very hard to see without a magnifying glass. Look for spiderlike webbing with small dots. The dots are the spider mites. Whiteflies closely resemble mealybugs, but they do not build nests. Whiteflies excrete honeydew, which can lead to sooty mold.

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.

Mealybugs and spider mites can be removed with an alcohol-dipped cotton swab. Whiteflies may require treatment with an insecticidal spray.

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.