Mulberry scale insects are sap-feeding pests that attack a wide range of trees and shrubs, including mulberry, citrus, and ornamental species. These insects belong to the armored scale group and are known for their protective waxy coverings, which make them difficult to control with conventional treatments.
While often overlooked due to their small size and stationary nature, mulberry scale infestations can cause significant plant stress over time. Heavy populations can lead to reduced growth, branch dieback, and even plant death if left unmanaged.
The Snow-Covered Bark: White Mulberry Scale
The White Mulberry Scale (Pseudaulacaspis pentagona) is a highly polyphagous armored scale insect that has spread across the United States, from Florida to the Pacific Northwest. Despite its name, it is a major pest of many fruit and ornamental trees, including Peach, Cherry, Privet, and Catalpa. In heavy infestations, the sheer number of male scales can make tree trunks appear as if they have been flocked with artificial snow or whitewash.
Identification and Sexual Dimorphism
This species exhibits a striking difference between the sexes, which is key to identification in the field. Identifying the scale accurately is the first step in effective management:
- The Female: The female scale cover is roughly circular, about 2.0 to 2.5mm in diameter, and ranges from white to yellowish-gray. It has a distinct “nipple” (exuviae) located off-center.
- The Male: Male scales are much smaller, elongated, and stark white. They often cluster in massive groups, creating the “snowy” appearance on the bark of the host tree.
- Armor: Unlike “soft” scales, the Mulberry Scale is an “armored” scale, meaning the waxy cover is not attached to the insect’s body, providing it with a superior shield against contact insecticides.
Internal Damage and Dieback
As these pests drain the plant’s sap through their piercing-sucking mouthparts, they do not excrete honeydew (a common trait of armored scales). Instead, the damage is purely physiological. Symptoms include reduced tree vigor, yellowing leaves (chlorosis), and branch dieback. If left untreated for several years, a heavy infestation can eventually kill young trees or significantly reduce the fruit yield of mature orchards.
Management: The “Crawler” Window
In the U.S., these scales typically produce two to three generations per year. Because the adults are protected by their armor, control efforts must be precisely timed to the “crawler” stage—the only time the young insects are mobile and unprotected. Management strategies include:
- Dormant Oils: Applying highly refined horticultural oils during the winter can smother the overwintering fertilized females.
- Scrubbing: For small ornamental trees, the white crust can be physically scrubbed off with a soft brush and soapy water to reduce the population.
- Biological Allies: Tiny parasitic wasps (such as Encarsia berlesei) are highly effective at controlling populations if broad-spectrum pesticide use is minimized.
Identification
Mulberry scale appears as small, circular, white to grayish bumps on bark, stems, and sometimes leaves. These bumps are actually protective coverings under which the insects feed. Infestations often begin on branches and can spread across the entire plant.
Life Cycle
The life cycle begins with eggs laid beneath the female’s protective covering. Once hatched, tiny mobile nymphs known as crawlers disperse to new feeding sites. After settling, they develop protective coverings and become immobile. Multiple generations can occur annually in warm climates.
Damage and Impact
Mulberry scale insects feed by piercing plant tissues and extracting sap. This reduces plant vigor, causes yellowing leaves, and can lead to dieback in severe cases. Unlike soft scales, armored scales do not produce honeydew, but their feeding still significantly impacts plant health.
Prevention and Control
Control involves applying horticultural oils during the dormant season to smother overwintering scales. Monitoring crawler emergence is critical for timing treatments effectively. Natural predators, such as lady beetles, can also help manage populations. Pruning heavily infested branches is recommended in severe cases.