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Lecanium Scale

Lecanium Scale Description

A lecanium scale is a semi-globular, soft-bodied, brown scale insect found on many shrubs and shade trees in the landscape. It overwinters as an immature nymph on the branches of infested trees. In spring, during April and May, scale start feeding and reproducing. An adult female can lay several thousand eggs. Upon hatching, crawlers reposition themselves and start sucking the juices from the branches they occupy. By the end of the summer, the scale develop a thin, soft, waxy shield.

Lecanium Scale Damage

Usually, the first indication of a scale problem is a tree or shrub with stunted growth and poor vigor accompanied by some dieback. Closer inspection of the twigs often reveals a heavy scale population that appears to be roped along the twigs. The scale excrete heavy honeydew (a sticky, sugar-rich substance) upon which a fungal growth known as sooty mold develops. Leaves of the host tree, as well as everything else underneath the canopy (other plants, garden furniture, driveways, etc.), turn black as a result of sooty mold.

lecanium scale

Figure 1a. Sooty mold that has developed on scale honeydew (liquid excrement) on a maple leaf. 
Figure 1b. Lecanium scale insects on a maple twig.

Lecanium Scale Control

Dormant oil at 2 to 2.5% concentration is a very effective application to treat scale infestations. Treatments should be applied in spring or late fall. Since the oil will soften the plant tissues, making them more susceptible to frost injury, make sure that temperatures do not drop below freezing for at least 24 to 48 hours after the application. As an alternative, trees can be injected with a systemic insecticide (ArborJet® or Mauget® System) that provides season-long control. Fertilization is strongly recommended to help restore the plant’s lost vigor.

Mirjana Bulatovic-Danilovich, WVU Extension Specialist, Consumer Horticulture – Agriculture and Natural Resources - Download PDF