[This post has been modified from the article originally published in the Fall 2018 issue of the Retail Nursery and Garden Center IPM News.]
As a home gardener, you may find big white bugs clinging to the twigs and leaves of your citrus trees and need help with identifying and managing these pests. At first glance, they may look similar but in order to have effective pest management, it's important to first determine what they are. Mealybugs and cottony cushion scale are common pests on backyard citrus trees that can easily be mistaken for one another.
Mealybugs
Mealybugs (Figure 1) are soft, oval, wax-covered insects that feed on many plants in garden, landscape, and indoor settings. These insects suck plants juices as they feed and can produce abundant honeydew which can in turn lead to sooty mold. Mealybug feeding can also reduce tree vigor and damage fruit. Colonies of mealybugs hide in crevices so light infestations might be missed.
Mealybugs are very difficult to control with insecticides. Instead encourage, conserve natural enemies by reducing ant numbers and dust. As with citrus leafminers, many natural enemies feed on and kill mealybugs. Some include common predators such as mealybug destroyers, lacewings, and spiders.
Clusters of mealybugs can be physically removed by handpicking or pruning them out. A high-pressure water spray repeated daily can also reduce populations.
The Pest Notes: Mealybugs contains more information about citrus mealybugs and other common mealybugs.
Cottony Cushion Scale
Cottony cushion scale (Figure 2) is most easily recognized by the female's elongated, fluted white cottony egg sac which can be about ½ inch long. These insects can infest both citrus and some woody ornamentals. Like mealybugs, they suck plant juices and produce profuse amounts of honeydew which attracts ants and allows growth of sooty mold. Cottony cushion scale decreases the plant's health by sucking sap, and heavy infestations can cause branches to die.
In most regions of California, cottony cushion scale is well controlled by natural enemies; the red and black lady beetle called the vedalia beetle, or a parasitic fly. Insecticides don't control adult cottony cushion scale very well and may kill their natural enemies, allowing even more growth of the scale insect.
See the Pest Notes: Cottony Cushion Scale to learn more about this pest.
Looking for other citrus insect pests? Check out our related posts on citrus leafminer, Asian citrus psyllid, and ant control for Asian citrus psyllid.