Scale on euonymus

Euonymus is notorious for scale problems, and the euonymus scale (Unaspis euonymi) is one of the most common armored scale insects on ornamental shrubs in the eastern US. Unlike soft scales that merely weaken plants, heavy euonymus scale infestations regularly kill individual branches and entire.

Euonymus is notorious for scale problems, and the euonymus scale (Unaspis euonymi) is one of the most common armored scale insects on ornamental shrubs in the eastern US. Unlike soft scales that merely weaken plants, heavy euonymus scale infestations regularly kill individual branches and entire plants. Euonymus fortunei (wintercreeper) and related species are particularly vulnerable.

I don't grow euonymus at my Long Island property — the deer pressure and disease susceptibility have kept me away from it — so this guide draws on Cornell Cooperative Extension, Penn State Extension, and Clemson HGIC research.

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The pest

Euonymus scale (Unaspis euonymi) is an armored scale, meaning the female insect secretes a separate hard waxy cover (the "armor") that is not attached to her body. Per Penn State Extension, euonymus scale has two very distinct sexes that look completely different:

• Female scale: brownish-black, pear-shaped, 1.5–2mm long; encrusted directly on stems and branches; easily mistaken for part of the bark
• Male scale: white, elongated, 1mm long; produced in massive numbers, covering leaves and stems with what appears to be a white powdery or thread-like coating

Per Cornell Cooperative Extension, the white male scales on leaf surfaces are often the first visible indicator of infestation — the white coating on euonymus leaves is not a fungal disease but male scale covers.

The species has two generations per year in most of the mid-Atlantic and Southeast.