What to do about cottony cushion scale, a common pest of citrus
Q. What are these weird white things on my citrus trees? They don’t seem like they’re moving, but they sure do attract ants!
Cottony cushion scale is a common pest of citrus, but can also infest other outdoor woody plants, particularly nandina and pittosporum. Usually, they can be found on new twiggy growth at the base of leaf petioles. The scale itself is rather small and golden brown in color. What you notice is the large egg sac she carries around like a white pleated oversized backpack. That “backpack” is loaded with 600-800 eggs that will eventually hatch into crawlers.
The crawlers are tiny and have red bodies with black legs and antennae. The crawlers produce a white, fluffy cottony-looking secretion (thus the “cottony cushion” in the name). As they grow, they shed these secretions/shells and keep producing white secretions until your tree is covered with them.
Like most scales, they damage plants by sucking the juice out through their mouthparts. A light infestation may not do much harm, but they can reproduce quickly into unmanageable numbers. They will secrete large amounts of honeydew, which attracts ants. The ants like the sticky, sweet honeydew and will “farm” scales, taking the honeydew back to their nests while protecting the relatively defenseless scale from predators. If you are dealing with a scale or aphid problem, your first step should be to control the ants. This can be done by using Tanglefoot, a sticky substance that is applied to tree trunks as a barrier that will exclude ants from reaching their free dinner. When using Tanglefoot, wear disposable gloves because it’s almost impossible to get off your hands. Wrap the trunk with paper or some other barrier since Tanglefoot can damage bark. You will want to monitor and replenish the Tanglefoot periodically since the ants will pile up and their friends will simply crawl over their stuck comrades to get into the tree. Ant bait can also be placed around the base of the tree and is less messy.
The Vidalia beetle is a natural enemy of cottony cushion scale and can be found throughout Southern California, especially in the drier inland regions. This beetle, also known as the ladybug or ladybird beetle, eagerly devours the squishy, juicy crawlers. The beetle’s larvae look fierce with their red and black, spiky-edged shells, but they have the appetite of a teenage boy, so if you see them, don’t kill them.
In cases of extreme infestation, you may want to use some sort of pesticide. Horticultural oil will probably be your best bet since it won’t kill the good bugs. Sprays are only effective against the crawlers since the adults like to hide in inaccessible places and their big eggsacs protect them from insecticide. Avoid using Imidacloprid (Merit or Bayer Advanced for Citrus) since it won’t work against the scale and will kill Vidalia beetles and other beneficials.
Los Angeles County
mglosangeleshelpline@ucdavis.edu; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/
Orange County
ucceocmghotline@ucanr.edu; http://mgorange.ucanr.edu/
Riverside County
anrmgriverside@ucanr.edu; 951-955-0170; https://ucanr.edu/sites/RiversideMG/
San Bernardino County
mgsanbern@ucanr.edu; 909-387-2182; http://mgsb.ucanr.edu