Q: What is this white stuff on my prickly pear cactus?
A: Thanks for bringing in a sample. The pest is actually called a cochineal insect. Prickly pear cacti (Opuntia spp.) are native to the Americas. They are easy to grow and propagate making them an excellent choice for low water use landscaping. For fun, carefully scrape some of wax mass from the plant with a knife and crush it on a piece of paper. If this results in a deep red color, then you know you have the cochineal scale (Dactylopious spp.)
Cochineal remained one of the most important sources of red dyestuffs until the 1850s, when the first synthetic dyes, called aniline dyes, were produced. Cochineal is still commercially produced in Mexico and India to furnish the permanent brilliant red dye for foods, drinks, cosmetics and artists’ colors. The dye made from cochineal is often called carmine or carminic acid. You may want to look for these ingredients on the labels of some of your favorite shampoos, gelatins, fruit juices, candies, and other red-colored products.
The cochineal scale is a piercing/sucking insect which uses the cottony wax to shelter female insects and egg masses. The crawler stage is when they spread on and among cactus plants. Once settled, they spin the waxy fiber to protect them from predators and the weather. While these small insects utilize the plant for food, the damage is usually negligible. If a plant is seriously colonized and showing signs of decline, you can prune off the worst pads and discard them (always prune at the joints). Blast the remaining portion of the plant with a high pressure hose. This should expose and weaken the insects. Then spray the exposed scale with and insecticidal soap.