Stapeliads on the whole are robust plants that aren’t vulnerable to many problems. The two maladies to be on the watch for are root rot and mealybugs. When a plant falls ill, I find it often has both: plants stressed by mealies more easily succumb to root rot, and plants weakened by a run-in with root rot will attract mealybugs.

Mealybugs

Boo. Hiss. Plant owners are no fans of mealybugs. Unfortunately mealybugs are a fan of many cacti and succulents including stapeliads!

“[Chorizococcus brevicruris] is considered a rather serious pest of succulent plants, Huernia spp. and Stapelia spp., belonging to the plant family Asclepiadaceae, growing in many nurseries throughout California.” (p. 95)

Color plate from Mealybugs of California with Taxonomy, Biology and Control of North American Species, by Howard L. McKenzie with color illustrations by Mary Foley Benson, 1967. 

Inspect

One of the reasons mealies like stapeliads is because their compact growth form which provides hiding places. They tend to infest the roots and crown first, so lightly lift the edges of your plant to check for white cottony substance where stems contact the soil.

Next check the nooks and crannies around the base of the plant, especially where stems branch or overlap. Then skip up to the tips of the stems, where the tight folds of new growth can hide them—sometimes all you can see are white speckles on the ends!

Take misshapen and stunted growth as a warning sign. An infested plant will suffer so keep an eye out for tops that are bent or curling over like this stapelia grandiflora. Tops often curl a bit naturally, especially on hanging stems, so it may not always be obvious at first.

If everything looks clean it’s still possible mealybugs are in the roots or dirt. Don’t harass your plant’s roots just to check unless you have reason to suspect infestation. Repotting is always a good time for a wellness check! Otherwise simply take preventive measures and take a close look at your plants regularly. 

Treat

When you discover a plant is infested, plan to treat and repot. There are several easy home-treatment options that will kill mealies, in no particular order:

• Rubbing alcohol: 91% isopropyl alcohol, use in a spray bottle or dab directly on insects with q-tips.
• Dawn dish soap: a small amount in water in a spray bottle works wonders on a lot of garden pests including ants. Less than half a teaspoon is plenty.
• Horticultural sulfur: say, didn't I mention this for root rot too?! Sulfur can kill and help dissuade mealybug infestations, as well as spider mites. Sprinkle on the soil as a preventative, or mix in water to give your plants a spritz.
• Insecticidal soaps: there are a lot of options available at your local nursery supply, like Safer Brand Insect Killing Soap.
• Neem oil: neem is always a solid choice, and works as a preventative as well as an insecticide. Follow direction to make a spray of neem oil in water.
• A witch's blend of these: people often use combos of these, like dish soap and alcohol. I often use multiple, and alternate between techniques to keep mealybugs on their toes.

Use water to clean as much dirt from the roots as possible, then spray down (or soak) the entire plant and its roots. You can use Q-tips or a paintbrush to get your mealybug killer into all areas of the plant, since they pests will wedge themselves into tight folds that won't get wet when doused. Be careful not to leave the plant out in direct sun after treatments using alcohol and neem oil which can cause burns.

Also spray down the pot to sterilize it, since mealybugs will live along the edges of the soil and leave dusty white residue on the pot. Treat the soil as infested: mealybugs may leave their cottony eggs (ovisacs) in the dirt and can burrow into the soil to molt. Some people recommend baking or otherwise sanitizing the dirt for reuse, but I douse it and throw it away. It may seem wasteful but mealybugs can really wreak havoc! I also throw away heavily infested sections of the plant.

Retreat

One treatment usually is not enough to catch all mealybug eggs and adults. Plan to re-treat for several days. You can leave cacti and succulents bare-root during this period. Once repotted, continue to check new plants regularly for signs of mealies you may have missed.

An infected plant can be so large and mature it's not practical to repot without fully dismantling the plant... which is unfortunately what you need to do sometimes. To treat without repotting, make a large batch of your preferred insecticide and SOAK the soil in the pot, and any rock top-dressing (don't do this with sulfur though, which can build up in the soil). At the same time thoroughly spray down all above-ground growth, moving branches to get under and between them.

I have been concerned about burning the roots so I run a rinse with plain water after, but so far the plants have seemed unaffected by this treatment. Don’t be too shy! The larger risk is overwatering the plant and causing root-rot if it’s unable to dry out quickly.

Prevent

Where do mealybugs come from? The depths of hell. I’m convinced they can materialize from the aether; they are sneaky little demons and it can take some care to keep your plant collection clean. A few quotes from Mealybugs of California (1967), p. 19–20, illustrate how tenacious this pest is:

“Specimens [of Scaptococcus milleri] have been discovered at least ten feet away from any vegetation”

“Many mealybug species are found under rocks, deeply embedded in cracks.”

“...some mealybugs are capable of finding their annual hosts before the first shoots break the soil surface.”

To avoid mealybugs, it’s always recommended to inspect, repot, and quarantine new plant purchases. Plants from big box stores commonly have pests. A lot of locally-owned nurseries do too.* Plant lovers recommend quarantining new purchases away from your collection. I always repot in my own soil as soon as possible and throw away the original soil. While you’re repotting it, closely check the base of the plant and roots for signs of mealybugs (you will occasionally get tricked by rooting hormone or a piece of perlite wedged between stems). Treat and quarantine as necessary.

Will all this care and quarantine keep your collection clean? No. Absolutely not. I had an existential crisis the day I came across a mealybug in the weeds out front of my house and it suddenly dawned on me that they can come from nature. No matter how careful you are quarantining new plants, mealybugs might find their way in anyway.

As quoted, mealybugs can wedge into cracks in rocks so sanitize any rocks from infected pots. Avoid putting your stapeliads in wooden planters, since the wood planks are another of mealies’ favorite habitats. In the winter, ensure greenhouse conditions don't grow too humid. I also learned the hard way not to keep pots directly on the ground where mealybugs and ants, their partners-in-crime, have easy access to roots.

Your stapeliad may respond well to frequent watering and fertilizer, but it will also make it more likely for it to attract mealybugs. For your plant to be in ideal health, it actually needs some stress! I know I said stress causes root rot and mealybugs, but it’s about good stress: some stress, but not too much. Think about it like trying to mimic what the plant would experience in nature versus pampering it. Pampering will invite mealybugs. In nature it has poor nutrients and it’ll get thirsty and shrivel sometimes. Many stapeliads will take on beautiful purple sun-stress colors when they get sunlight, so don’t be afraid to put it somewhere semi-exposed. 

 

* No shade to local nurseries, in all fairness you gotta be vigilant having that many plants in close proximity, and having just one supplier with pests can introduce an infestation. Most nurseries operate with good intentions surrounding pest control but mealybugs are notoriously sneaky. As the houseplant and exotic plant industry has been expanding rapidly in recent years, unfortunately a commercial industry has ballooned where less and less care seems to be put into plant health, as long as it looks good for long enough to sell—if even that, we’ve all seen the rows of dead plants at Walmart. Box stores have grown notorious in the hobby for introducing pests to peoples' collections, so use caution.