I have a sticky substance dripping from my Christmas cactus. I’ve never experienced this before. What is it?
It sounds like you have a pest that produces honeydew. Look carefully at the plant – do you see small insects in the folds or new shoots of the plant, or perhaps oval shaped bumps? The insects could be mealy bugs, aphids, or white fly. The bumps could be scale. These insects usually congregate in groups, and all suck the sap from the host plant. The sticky stuff is called “honeydew” and that is what is excreted by the insect.
For any of these pests, isolating the plant from other house plants until treatment is complete is important – it will prevent spreading. The insects must be removed, and each are treated differently, but using the same product, insecticidal soap, either as a spray, wash or soak. Always read the directions for each solution.
Scale are insects that can be sprayed with insecticidal soap while in the larval or crawler, stage. Since we almost never see them at that stage, manual removal of the later stage hard scale or bump is needed. Usually, a cloth with insecticidal soap soaked into it will wipe them away. Treat until clear.
Aphids are soft bodied insects that can easily come off with a swipe of your finger. If that’s too squiggy for you, a cloth with insecticidal soap wiped over them will get them too. Spraying with insecticidal soap solution also works. Spray or clean every few days, as eggs hatch with new aphids. Treat until clear.
White fly are poor fliers, but are difficult to catch. According to the New York Times 1000 Gardening Questions and Answers (2003), intense sanitation is the key. They suggest dipping the plant upside down in a tub of water mixed with insecticidal soap, and swishing it around. They even mention flypaper to catch the little flies. Either way, that’s for the adults. To kill eggs, you must drench the soil, where the eggs are deposited, with water and diluted insecticidal soap to remove them. Then run clear water through the pot. Let the soil dry completely before watering.
Mealy bugs are a type of scale, and are recognizable by the fluff; a female with an egg case in a protective cover. The crawlers that hatch are quick movers, so the New York Times (2003) suggests a bath in insecticidal soap solution every three weeks will eventually solve the problem.
For further information on care, check out a previous Master Gardener answer: