There are a dozen or so species of soft scales in the United States and Canada that were previously all classified in the genus Lecanium in the family Coccidae (soft scales). Lecanium scales are now considered to be in different genera, as they have since been reclassified from the original Lecanium genus. Lecanium scales are difficult to identify and distinguish from one another. It will often take a specialist (a soft scale taxonomist) to accurately identify these insects. Taxonomy of this group is still in question, and will likely be revised in the future. Some species are host specific and only occur on a few hosts, whereas others are highly polyphagous and found on many different host plant genera. The more common pest lecanium scale species can often be identified in the field for the purposes of management if one knows the size of the scale, its habits and life cycle, and host plants. Lecanium scales are soft scales, and as such do not possess a waxy coating or "test". The exact timing and location of the life cycle of these insects depends upon the species, but in general it can be thought of as the following. After the female lays eggs, her body dries and becomes brittle and brown. The length of the female varies from 3 to 12 mm and her dried body is often mistaken as a scale cover. The body of the female covers the eggs and remains in place until the eggs hatch. Many lecanium scale life cycles are similar. Most of their active feeding and thus damage to the host plants occurs from the spring to early summer. By late spring or early summer, eggs may be found beneath the females. Crawlers (mobile immature stage) emerge from beneath the females and migrate to the leaves (or elsewhere depending upon the species) where they settle to feed. This typically occurs between June and July. Crawlers may move to the twigs prior to leaf drop. For many lecanium scale species, there is only one generation per year. However, life cycle information is species-specific and should be researched as appropriate.
*Examples of species of lecanium scales include but are not limited to: the calico scale (Eulecanium cerasorum), large hickory lecanium (Eulecanium caryae), fletcher scale (Parthenolecanium fletcheri), European fruit lecanium (Parthenolecanium corni), and the oak lecanium (Parthenolecanium quercifex). Each are matched up with possible host plants above (Johnson and Lyon, 1991). For many of them, specific life cycle information is provided elsewhere in this guide.
Adult lecanium scales may be found on twigs and small branches, depending upon the species, with part of the crawler stage possibly occurring on leaf surfaces. Lecanium scales use piercing-sucking mouthparts to feed on their host plants. Lecanium scales feed by inserting piercing-sucking mouthparts into their host plants to remove fluids. Moderate or heavy infestations of these insects can lead to the production of honeydew, which can attract stinging insects and support the growth of sooty mold. Heavy or prolonged infestations of certain species may cause leaf drop, stunted growth, and twig dieback, especially following maturation of the females and associated feeding in mid-spring into early summer. Young trees growing with poor site conditions, or newly transplanted trees may be the most susceptible.
Monitoring for lecanium scales will vary depending upon the life cycle of the species, however in general the overwintered life stage develops into mature females in the spring. As the females mature into adults, they become swollen and rounded which may make them more visible when scouting. Additionally, this can (for certain species) be a time of copious honeydew production, or the excretion of sugary liquid excrement. This may also be visible on leaves, branches, or other surfaces beneath trees with a population outbreak of lecanium scales. On top of the layer of honeydew, a black colored sooty mold (fungus) may grow. In the fall and winter, nymphs (immatures) may be visible (with magnification) on the twigs of the host plant. This can be a helpful time of year to scout, particularly if your area is having an outbreak of lecanium scale activity, so dormant oil applications can be planned. In the summer, crawlers may be visible on leaves near the veins, but often magnification is also needed for this life stage as well.
Individual, heavily infested branches may be pruned from the host plant and destroyed to reduce the population on a single ornamental plant. If the tree is extensively covered in lecanium scales, do not over-prune to risk further harming the health of the host plant. In some cases, if they can be safely reached, scrubbing scales off with a soft brush or syringing them with water may be an option. Prevention of host plant stress from other factors can also help reduce the impact of lecanium scale activity. Plants near reflective surfaces (pavement, walls, etc.) may also be more prone to heavy scale populations due to microclimate changes in these areas.
Depending upon the species of lecanium scale, their populations are subject to rapid increases or decline. Changes in abiotic conditions can play an important role in their populations, but many parasitoids and predators also feed on these insects as well. Many natural enemies are helpful at regulating lecanium scale populations, but during outbreaks may not be effective on their own in managing them on ornamental trees and shrubs. However, these natural enemies should be preserved and taken into consideration if using chemical management options (least toxic options should be selected). Species specific information about predators, parasites, and pathogens of lecanium scales may be found in other sections of this guide.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL) (Labeled for soft scale crawlers)
Cyantraniliprole (NL)
Cyfluthrin (NL) (Labeled for scale crawlers)
Dinotefuran (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L) (Labeled for soft scale crawlers)
Insecticidal soap (NL)
Lambda-cyhalothrin (L) (Labeled for scale crawlers)
Neem oil (NL)
Pyrethrin + sulfur (NL)
Pyriproxyfen (L) (Labeled for scale eggs)
Spinetoram + sulfoxaflor (N)
When used in nursery settings, chlorpyrifos is for quarantine use only.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), imidacloprid (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.