Q: I have prickly pear cactus that has white patches on the pads that looks like little bits of cotton. What is this, and is this bad for the plant?
A: Most likely what you are seeing on your cactus is an insect called cochineal scale. These insects cover themselves with a waxy coat that appears like white, cottony tufts. To verify this is what you have, you can crush one of them to see if it leaves a bright, red stain. This red material is the blood of the insect, and its color is due to the presence of carminic acid. Humans use this to produce carmine dye for various things including food coloring and lipstick.
Scale insects insert their mouth parts into the cactus to feed on the sap, and over time can reduce the vigor of the plant. You can help your cactus by spraying the insects with a hose periodically and/or using insecticidal soap.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to
