Scale insects on magnolia

Scale insects are among the most damaging pest groups for magnolias, and they go undetected longer than most pests because the adult stages are immobile and look like part of the plant's bark. By the time sooty mold blackens the leaves below heavily infested branches, a scale population may have.

Scale insects are among the most damaging pest groups for magnolias, and they go undetected longer than most pests because the adult stages are immobile and look like part of the plant's bark. By the time sooty mold blackens the leaves below heavily infested branches, a scale population may have been building for two or more years.

The magnolia scale (Neolecanium cornuparvum) is the largest scale insect in North America and is nearly exclusive to magnolias. It is the species home gardeners encounter most often. I don't grow magnolias at my Long Island property, so this guide draws on Cornell Cooperative Extension, Penn State Extension, and Clemson HGIC publications.

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The pests

Magnolia scale (Neolecanium cornuparvum)

Per Penn State Extension, magnolia scale is the largest soft scale insect in North America. Females can reach 0.5 inch (12mm) in diameter — large enough to be visible on branches without magnification. They appear as smooth, convex, shiny brown bumps, often covered in a white waxy powder. Multiple females may be packed together along twigs and young branches.

Magnolia scale has one generation per year. Per Cornell Cooperative Extension, it overwinters as immature nymphs on the bark of magnolia twigs. Adults mature in summer; females produce live crawlers (tiny, mobile nymphs) in late August–September. The crawler stage is the most vulnerable to contact insecticides.

Other scale species on magnolia

Per Clemson HGIC, other scale species occasionally infest magnolias including white prunicola scale and various armored scales, but magnolia scale is the most common and most damaging in the eastern US.