The sycamore, encompassing species like the American sycamore (Platanus occidentalis) and the popular hybrid London plane tree (Platanus x acerifolia), is a widely planted tree known for its impressive size and distinctive, peeling bark. These trees are generally quite resilient, making them a favorite for shade and ornamental landscaping in urban and suburban environments. Despite their hardy nature, sycamores are susceptible to a few specific insect pests that can cause noticeable damage to their foliage and wood. Understanding how to identify these common pests and the nature of the damage they inflict is the first step in maintaining the long-term health of these trees.
Key Insect Pests and Identification
Two of the most frequently encountered pests for sycamore owners are the sycamore lace bug and the sycamore scale, both of which feed on plant sap. The Sycamore Lace Bug (Corythucha ciliata) is a tiny insect, measuring about one-eighth of an inch long, distinguished by its delicate, lacy wings and hood-like structure covering its head. Adults often overwinter in the crevices of the tree’s bark, emerging in the spring to lay eggs on the underside of new leaves.
Lace bug nymphs and adults use piercing-sucking mouthparts to feed on the leaf tissues, primarily on the underside. This feeding results in a characteristic white or yellowish stippling visible on the upper leaf surface. A clear sign of their presence is the accumulation of tiny, dark, varnish-like droplets of excrement, known as frass, coating the leaf undersides. These insects have several generations throughout the warm season, with populations typically peaking in late summer when damage becomes most apparent.
The Sycamore Scale (Stomacoccus platani) presents a challenge because of its minute size, often measuring less than one-sixteenth of an inch, making the insects themselves difficult to spot without magnification. These scales are primarily identified by the symptoms of their feeding, which includes yellow or orange spots on the undersides of leaves. White, cottony, waxy masses found in bark fissures also indicate their presence. Unlike many other scale insects, adult sycamore scale remains mobile throughout its life, moving between the leaves and the bark.
A third pest is the Sycamore Borer (Synanthedon resplendens), a clearwing moth whose larvae tunnel into the bark and wood of the tree. The adult moth mimics a wasp, but the damage is done by the larval stage. Larval activity is identified by the reddish-brown, sawdust-like material, or frass, extruded from the bark. Borers tend to target older trees that are already under stress, favoring areas where the bark is damaged or cracked.
Distinguishing Between Cosmetic and Serious Damage
The damage caused by common sycamore pests ranges from unsightly to genuinely harmful, making accurate assessment important for deciding on a course of action. Damage caused by sycamore lace bugs is overwhelmingly considered cosmetic, affecting the tree’s appearance rather than its long-term survival. The stippling and bronzing of leaves, along with premature leaf drop in late summer, can reduce the tree’s aesthetic appeal but rarely causes lasting injury to a healthy, established sycamore.
The sticky residue known as honeydew, produced by sap-feeding insects, often leads to the growth of sooty mold. This black, powdery fungus grows on the honeydew coating the leaves and branches. Sooty mold is also a cosmetic issue; it interferes with photosynthesis but does not directly infect the tree. However, the cumulative stress of severe, repeated lace bug infestations combined with environmental stresses like drought can weaken a tree’s overall vigor over multiple consecutive years.
In contrast, infestations by the sycamore scale or the sycamore borer cause serious damage that threatens the tree’s health and structure. Heavy scale infestations can lead to significant branch dieback and stunted growth, especially in young or newly planted trees that lack the resources to tolerate prolonged sap loss. Borers pose a structural threat as their larvae tunnel under the bark. While tunneling is often limited to the outer bark, extensive feeding can cause the bark to thicken, crack, or slough off, creating entry points for secondary pathogens and leading to branch decline or structural weakening.
Effective Management and Control Methods
Managing sycamore pests begins with cultural control aimed at maintaining the tree’s health, as a vigorous tree is naturally more resistant to insect attacks. Ensuring the sycamore receives proper watering, especially during dry periods, is one of the most effective preventive measures against pests like borers and scale, which often target stressed trees. Regular pruning to remove dead or heavily infested branches can also reduce the overall pest population before it spreads to healthy sections of the canopy.
Mechanical and biological controls offer environmentally sound options for managing lace bugs and scale crawlers. Simply using a strong jet of water from a hose can physically dislodge pests, especially the more vulnerable nymph and crawler stages, from the undersides of leaves. Encouraging natural predators can also help keep pest numbers low, as these beneficial insects consume lace bugs and scale. Beneficial insects include:
Lady beetles
Lacewings
Parasitic wasps
When infestations are severe, chemical control may be necessary, and the timing and type of product used are important for success. For lace bugs and scale, the most effective topical treatments are horticultural oils and insecticidal soaps, which work by suffocating the insects. These should be applied thoroughly to the underside of the leaves where the pests are actively feeding.
A dormant oil application in the late winter or very early spring, before leaves emerge, is effective against overwintering scale and lace bug adults and eggs. Alternatively, a targeted application can be made at bud break to coincide with the emergence of the vulnerable scale crawlers. Systemic insecticides, which are absorbed by the tree and move throughout the tissues, are also available for professional application and can provide longer-lasting control for both lace bugs and scale. Management of the sycamore borer, however, focuses almost entirely on prevention through tree health and avoiding trunk wounds, as systemic insecticides are not effective against this specific wood-boring pest.