Cactus scab is most commonly found on the Prickly Pear Cactus but may affect other varieties, as well. You may have noticed similar markings on your produce–scabbing is very common in tomatoes, cucumbers, and cabbage.
While it may look worrisome, scabbing is nothing to be afraid of. Cactus scabbing is a form of edema, or patch of abnormal cell growth. Scabbing almost always occurs on the oldest parts of the plant.
To discourage additional scabbing, here are some things to consider:
Keep your cactus away from any cool breezes or drafts, especially in the winter months. Cacti like to be kept cozy and warm.
Is your cactus getting enough light? Cacti prefer bright indirect light, but can tolerate lower light in the winter months, when growth naturally slows.
Make sure you’re not overwatering! Water your cactus when it is almost completely dry. When you do water, make sure you’re completely saturating the soil–enough that water flows freely from the drainage hole at the bottom of the pot. It’s very important not to leave any excess water in the saucer. Your cactus doesn’t like “wet feet.”