Christmas cactus rarely suffers from any diseases but can be susceptible to root rot if planted in a potting mix with poor drainage.
If your Christmas cactus stems are starting to mold, use a sharp sterilized blade to remove the damaged sections.
You can tell if your Christmas cactus has root rot when the stems are starting to wilt, turn yellow, or develop soft, brown spots. Take the plant out of the pot and inspect the roots.
If you notice small flies on the soil and around your Christmas cactus, they’re fungus gnats. These insects thrive in nutrient-rich, moist soil, and although adults are harmless, the larvae can damage the plant and spread fungal diseases.
Christmas cactus can be susceptible to mealybugs, a type of insect that drinks sap and forms soft, white clusters on the stems.