Q: I have white cotton clusters on my prickly pear cactus. What effect do they have on prickly pear cactuses? What is it and what should I do about it?
A: Many of us have prickly pear cactus growing in our landscapes. Prickly pear cactuses are native to the Americas, from South America to the Arctic Circle. They are easy to grow and propagate, and make an excellent choice for low-water use landscaping in Arizona.
The cochineal scale (a sucking insect that’s native to Arizona) grows at the base of needles of prickly pear cactus, forming a mass of stringy whitish globs. 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 at the joints and discard them. Insecticides aren’t very effective because the white fuzz protects them.
Blast the remaining portion of the plant with a high-pressure hose. Then spray the exposed scale with an insecticidal soap or a mixture of 1/2 teaspoon of dish soap to one gallon of water. The water jet knocks off the fuzz and the soapy water will then dissolve their waxy coating and they will die from exposure.
Carefully scrape some of wax mass from the plant with a knife and crush it on a piece of paper. If the result is a deep red color, then you have just discovered crushed cochineal scale. Cochineal scale uses the cottony wax to shelter female insects (that produce the red dye) and egg masses. The eggs hatch into crawlers that feed for about three weeks before settling and becoming immobile. The crawler stage is when they spread on and among cactus plants. Once settled, they spin the waxy fiber that shelters them from predators and the weather. Multiple generations are produced each year in warmer areas.
As the Spanish discovered when they conquered Mexico in 1521, the cochineal scale, when crushed, yielded a supreme scarlet dye the Aztecs used in the production of exquisite textiles.
The dye became an added incentive for Spain in its Mexican conquest. The cochineal — the Spanish held the source of the dye secret for years — produced a major cash export from Mexico, second only to silver.
The cochineal still serves as the source of the dye that microbiologists use to stain slide specimens. 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.