Purple Scale

If you have a citrus tree, you may want to take a closer look for signs of purple scale in late spring and early summer, and again in autumn.

Purple scale feeding on an orange (Michal Maňas) CC BY 3.0

​Purple scale identificationPurple scale insects suck the sap from citrus trees and they look like miniature mussels. Also known as mussel scale, orange scale, and comma scale, purple scale (Lepidosaphes beckii) are a type of armored scale that attach to banana, bay laurel, citrus, fig, mango, pear, and stone fruit trees and grapevines. These pests have several ornamental hosts that bear inspection:

Purple scale damage

Like other scale insects, purple scale feed predominantly on leaves and young fruit, but they will attack all parts of a tree. You may see tiny yellow halos on the leaves. Purple scale feeding can weaken branches, disfigure fruit, and reduce productivity. Heavy feeding can lead to defoliation and twig dieback. In extreme cases, the tree can die.
 
Populations of purple scale are usually low and found mostly in coastal regions, but mild temperatures, high humidity, and overcast skies can provide the conditions needed for a population explosion. You can find these pests in the cooler, shaded areas of trees.

• Agave (Agave sisalana)
• Cypress (Cupressus)
• Hibiscus
• Holly (Ilex)
• Myrtle (Myrtus)
• Oak (Quercus)
• Orange jasmine (Murraya exotica)

• Orchids (Orchidaceae)
• Pine (Pinus)
• Peppercorn (Piper)
• Palms (Raphia)
• Roses (Rosa)
• Silverberry (Elaeagnus)
• Yew (Taxus)

Purple scale insects aren’t actually purple. That sure would make them easier to find! Instead, they are dark brown and may have tan edges with a slight purplish tinge.

Male purple scales are smaller and narrower than females. In both cases, you may see a slight bend at the narrow end of the scale. Male purple scales are 1/10” long and females are slightly larger. Male purple scale insects are tiny and they fly around in search of immobile females.

Purple scale (USDA) Public Domain

Purple scale lifecycle

Females lay 40 to 80 eggs under their protective covers. After the eggs hatch, crawlers emerge and scuttle to nearby fruit, leaves, and twigs, where they begin forming their own covers. At first, purple scale crawlers are covered with a mass of waxy threads. When they are about half-grown, their purplish-brown covers begins to develop. Once a female attaches herself, she stays put.

Purple scale management

Temperatures above 80°F are hard on purple scale, so their numbers are greatly reduced by the time summer is in full swing. But a second generation may appear in autumn and, in some years, a third generation may occur before winter cold brings them to a halt.

Natural predators, such as parasitic wasps, twicestabbed lady beetles, and Australian lady beetles, take a big bite out of these pests. We can help them do their job by avoiding broad-spectrum pesticides and applying sticky barriers to the trunks of trees. Argentine ants are known to protect scale insects, so sticky barriers remove that protection.

Purple scale prefer dusty conditions, so giving your citrus trees a quick shower with the hose can help.