White Residue on Shrubs: Powdery Mildew or Scale Insects?

A white residue on evergreen shrub leaves in southern Tennessee that recurs on different species suggests either powdery mildew or euonymus scale—two very different problems.

Distinguishing the Two

Characteristic	Powdery Mildew	Euonymus Scale
Appearance	Powdery, dust-like coating on leaf surface	Tiny, white, oyster-shell-shaped bumps on leaves and stems
Texture	Wipes off easily	Hard, attached; does not wipe off
Hosts	Many shrubs, especially in shade	Primarily euonymus, but also pachysandra, holly
Damage	Yellowing, leaf drop, reduced vigor	Yellow spots, leaf drop, branch dieback

Treatment for Each

If Powdery Mildew:

• Apply fungicide (sulfur, neem oil, or synthetic) per label.
• Improve sun exposure and air flow.
• Water at base, not on foliage.

If Euonymus Scale:

• Late winter/early spring: Apply horticultural oil (dormant oil) before new growth emerges to smother overwintering scales.
• Early summer (June): Apply insecticidal soap or horticultural oil (summer rate) twice, 10 days apart, to target crawlers.
• Repeat for 2–3 years for complete control.

How to Confirm

Search "euonymus scale images" online and compare to your plants. If unsure, take a sample to your local Extension office or nursery.

Key Point

Correct ID saves time, money, and prevents unnecessary pesticide use. Both problems are manageable with the right approach.