Cacti are famous for being the ultimate low-maintenance, tough-as-nails roommates. But even these desert warriors have their limits. If you’ve noticed a weird white coating developing on your cactus’s skin, it’s more than just an eyesore—it’s a sign that your plant’s health is taking a hit. Let’s dive into the most common culprits behind that white fuzz and, more importantly, how to fix it:
Cause #1: Powdery Mildew
If your cactus looks like it’s been dusted with white powdered sugar, you’re likely dealing with a fungal infection known as powdery mildew. If left unchecked, those white patches will eventually turn brown, and the affected parts of the plant will die off.
Here’s how to kick mildew to the curb:
- Prune away any heavily infected areas and toss them in the trash (don’t compost them!).
- Mix up a DIY spray using one part fresh milk and eight parts distilled or rainwater.
- Spritz this milk mixture onto your cactus every three days until the fungus disappears.
If you keep your cacti in a greenhouse, you can actually recruit some tiny helpers. Certain species of ladybugs (like the sixteen-spot ladybug) and hoverflies absolutely love snacking on fungal spores and will happily clean your plants for you.
Cause #2: Mealybugs
Does the white stuff look more like tiny, sticky cotton balls tucked into the ribs of your cactus? Then you’ve got mealybugs. These little armored pests and their larvae are parasites that suck the sap right out of your succulents. They leave behind a sticky, white residue, which is why they’re often called “scale insects” or “smear lice” in some circles.
To get an infestation under control, try these steps:
- For larger areas, you can spray the plant with rubbing alcohol or lemon balm spirit.
- For localized spots, dip a cotton swab in alcohol and dab the bugs directly to dissolve their protective coating.
- Alternatively, mix about one quart of water with a tablespoon of insecticidal soap (or pure castile soap) and spray the plant thoroughly.
Just like with mildew, nature has its own cleanup crew for mealybugs. The Mealybug Destroyer (a specific type of Australian ladybug) considers these pests a delicacy. You can actually order these beneficial insects from specialty garden suppliers to help police your collection!
