White Cactus Diseases

Mealybugs

• What appears to be a white disease on a cactus may in fact be infestation by an insect called a mealybug, a pest that regularly inhabits cacti and succulents. The mealybug produces tiny balls of white fluff on the plant or on the spines or at the base of the cactus. The bug feeds on the tissue of the plant and develops a covering of white, cottony wax. When several of the mealybugs cluster together, what looks like clumps of white cotton or fungus appear.

Mealybug Management

• Extensive infestation by the mealybugs slows the growth of the cactus and results in a collection of honeydew -- the waste of the insect. This sticky excrement causes the development of a black sooty mold as fungi are attracted to the honeydew. Encouraging the health of the cactus allows it to tolerate moderate mealybug feeding without suffering extensive damage. Insecticidal soaps may also be applied to the plant to reduce the population of mealybugs.

Cochineal Scale

• The insect called the cochineal scale (Dactylopius coccus) also causes what may appear to be a white cactus disease. Like the mealybug, this insect is covered with a white, waxy coating that mimics the appearance of white cotton balls attached to the pads and stems of the plant. Cochineal scale primarily infest prickly pear (Opuntia ) and cholla (Cylindropuntia) cacti. This presence of this pest can be diagnosed by crushing it; the presence of a red fluid indicates that the white disease is actually the scale insect.

Cochineal Scale Management

• The presence of large populations of cochineal scale over an extended period of time can kill a cactus. Cochineal scale are managed by the application of insecticidal soap or by the simple utilization of a hard stream of water to wash them away. Gardeners may also choose to utilize alcohol-dipped swabs to wipe the scale away and should keep in mind that insecticidal soaps may also kill beneficial insects, such as the natural predators that control the scale.