From our perspective as Orchid Cacti (Epiphyllum and related hybrids), we are generally resilient plants, but our succulent, flattened stems can be tempting targets for a variety of pests. Understanding these threats from our point of view is key to maintaining our health and vibrant blooms.
You will often find these pests nestled in the crevices where our stems join or on the undersides of our segments. They appear as small, white, cottony masses. From our perspective, mealybugs are particularly draining. They insert their piercing-sucking mouthparts into our tissues to feed on our sap. This weakens us significantly, causing our stems to become soft, yellow, and stunted. They also excrete a sticky substance called honeydew, which attracts ants and can lead to the growth of sooty mold, further inhibiting our ability to photosynthesize. To treat an infestation, we appreciate being isolated from other plants. You can dab individual mealybugs with a cotton swab dipped in isopropyl alcohol. For larger infestations, a thorough spray with insecticidal soap or neem oil, making sure to reach all the hiding spots, is very helpful.
Scale insects can be harder to spot because they look like small, brown, tan, or white bumps stuck firmly to our stems. They are another type of sap-sucking pest. Like mealybugs, they cause yellowing, wilting, and a general decline in our vigor. Their protective shell makes them resistant to many sprays. The most effective physical treatment is to gently scrape them off with a soft brush or your fingernail, being careful not to damage our delicate skin. Following this, an application of horticultural oil or insecticidal soap can help eliminate any crawlers (the juvenile stage) that you may have missed.
Spider mites are tiny arachnids that are difficult to see with the naked eye. You might first notice their damage as a fine, stippled yellowing on our green stems. If the infestation is severe, you will see delicate, silky webbing, especially between our segments. They thrive in hot, dry conditions. From our standpoint, a spider mite attack feels like being drained of life from thousands of tiny points, leaving our stems looking dull and speckled. Increasing humidity around us by misting can deter them. A strong spray of water can dislodge many of the mites. For persistent problems, miticides or neem oil applications are effective. It is crucial to treat the undersides of our stems where they prefer to congregate.
While the adult gnats are merely annoying to you, their larvae in the soil are a problem for our root systems. These tiny white larvae feed on organic matter and, when populations are high, will nibble on our tender roots. This disrupts our ability to take up water and nutrients, leading to poor growth above the soil. The key to controlling fungus gnats is to target their larval stage. Allowing the top layer of our potting mix to dry out completely between waterings is the most effective deterrent, as the larvae cannot survive in dry conditions. You can also use yellow sticky traps to catch the adults and reduce egg-laying.
Aphids tend to congregate on our tender new growth, flower buds, and open blooms. They are soft-bodied insects that come in various colors (green, black, red) and cluster together to suck sap. Their feeding can cause new growth to become distorted and buds to drop before opening. Like other sap-feeders, they produce honeydew. A strong jet of water is often enough to knock them off our delicate buds. Insecticidal soap sprays are also very effective against aphids if applied directly to the pests.
