Crape Myrtle Bark Scale (CMBS) is a common pest that impacts crape myrtle trees, a popular ornamental plant in many landscapes. This insect, originally from East Asia, was first identified in Texas in 2004 and has since spread across various southern states and northward. Understanding the life cycle of CMBS is important for effectively managing infestations and protecting the health and appearance of these trees.
Stages of the Crape Myrtle Bark Scale Life Cycle
The crape myrtle bark scale life cycle begins with eggs. Adult female scales lay numerous pink eggs, typically ranging from 60 to 300, within a white or gray felt-like egg sac called an ovisac. These eggs are laid from May to September, and they can also be the overwintering stage, along with nymphs, in bark crevices.
Within a week of being laid, the eggs hatch into the first nymphal stage, known as crawlers. These tiny, mobile insects are pinkish and possess legs and antennae, making them the only mobile stage in the scale’s life cycle. Crawlers are responsible for dispersing to new areas of the plant, preferring cracks and crevices on the bark to establish new feeding sites.
Once settled, crawlers molt into subsequent nymphal stages, losing their appendages and becoming sessile. These nymphs are pinkish and develop a denser, whitish waxy covering as they mature. Nymphs, along with adult females, feed on the plant’s sap by inserting their straw-like mouthparts into the phloem, extracting sugars.
Nymphs eventually molt into adult males or females. Adult females are wingless, sessile, and appear as white, waxy, cottony masses covering the bark. Adult males are winged and mobile, flying to find mates. The entire life cycle, from egg to adult, can be completed within two to three months, allowing for multiple generations per year, two to four.
Recognizing Infestation and Damage
The presence of crape myrtle bark scale is first noticed through visible signs on the tree’s bark. Infestations appear as white or gray, waxy crustations, concentrated in branch crotches, along stems, and at old pruning scars. These white, felt-like encrustations are the adult scale insects themselves.
A prominent indicator of CMBS activity is the secretion of honeydew, a sticky, clear, sugary substance excreted by the feeding scales. This honeydew coats leaves, branches, trunks, and surfaces beneath the tree. The honeydew then provides a medium for the growth of sooty mold, a black fungus that covers affected areas, turning the bark and leaves dark.
Beyond these visible residues, crape myrtle trees infested with CMBS may show other signs of stress. This can include reduced plant vigor, delayed leaf-out in spring, fewer and smaller flower clusters, and branch dieback. While CMBS may not quickly kill healthy crape myrtles, the extensive sooty mold can reduce photosynthesis, further weakening the tree.
Effective Management Strategies
Managing crape myrtle bark scale involves a combination of approaches. Promoting overall plant health through appropriate watering, proper fertilization, and planting in full sun helps trees better resist and recover from infestations. Physically removing scales by scrubbing smaller infestations with a soft brush and soapy water can help reduce populations and remove sooty mold.
Horticultural oils are an effective treatment, particularly against soft-bodied stages like crawlers and overwintering eggs or nymphs. Dormant oil, a type of horticultural oil, is applied in late fall to early spring when trees are defoliated, ensuring thorough coverage of bark crevices. During the growing season, summer oils can be used, timed to coincide with crawler activity.
Systemic insecticides, which are absorbed by the plant and move through its tissues, offer a longer-lasting control option. These are applied as a soil drench or injection in early spring as new growth begins, allowing the tree to take up the insecticide before the scale populations peak. Contact insecticides can also be used, targeting the vulnerable crawler stage when they are actively dispersing. Integrated Pest Management (IPM) combines these strategies, emphasizing monitoring for crawler activity and timing treatments for effectiveness while minimizing impact on beneficial insects.