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Index : Pests
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- 29. White Fuzz On Prickly Pears - Top
- Ever wonder what the fuzzy white substance is on your prickly pear cactus. Many people don't know. Many others think they're patches of a strange fungus. But actually, underneath all that white fuzz you'll find hiding little red insects called Cochineal Scale.
Like other scale insects, cochineal scale spends all of it's adult life securely attached to the leaf, or in this case pad. Here it feeds by piercing and drinking the plant juices. That's why on prickly pears were cochineal are feeding you'll notice the pads have turned yellow.
The white fuzz is actually a protective waxy coating produced by the scale to help protect itself from predatory insects and birds looking for a tasty meal. Young scale insects, called crawlers, are waxless. As soon as they hatch from eggs produced by the female cochineal, they crawl and disperse to other locations on the plant. They also crawl to the edges of the plant, spin a web-like filament, and let the wind carry them to a nearby prickly pear. Here they settle down, attach themselves to a spot, and begin forming their own wax covering.
One of the interesting things about cochineal (meaning scarlet-colored) is that they have been used since the early days of the Aztecs as a dye. Introduced into Europe by Cortez in the early 1500's, cochineal soon became favored as a red dye for everything from fabrics to paintings.
Later cochineal was also used as a food coloring. Cochineal scale can kill pads of prickly pear that are heavily infested. Entire plants can be killed, but this usually happens after years of infestation. This is not a fast spreading insect, nor one that is difficult to control.
The easiest way to control the scale is to prune off heavily infested pads. Since these insects begin feeding on the outermost pads, generally few need to be removed. Prune where the joint of one pad meets another. Don't remove just part of the pad by cutting it in two.
An even easier way to control the scale is to knock them off with a strong jet of water from a garden hose. This will remove the waxy covering and kill most of the insects hiding underneath.
Chemical sprays are not recommended because they will also kill the beneficial insects, such as lady beetles, which feed on this scale. If you must spray, use a soap solution. Soap sprays are not harmful to beneficial insects.
To make a soap spray, mix 1/4 teaspoon of a liquid dish washing soap in one gallon of water. Most any brand will do, however Dawn has been found to have the best pest killing properties. Whatever brand you select, don't use the lemon-scented types.
Many fascinating insects, such as cochineal, exist in the deserts of the Southwest. To find out more about them, I highly recommend the book "Insects of the Southwest". It's a great guide for identifying and learning about helpful, harmful, unusual, and venomous insects of Arizona. The author is Carl Olson, noted entomologist and faculty member of the University of Arizona. The book is published by Fisher Books and is available at local book stores and garden centers.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
Material originally appeared in Arizona Daily Star gardening column, on December 8, 1996
- Updated: December 8, 1996
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