White Powder on Privet Hedge: Scale Insects or Powdery Mildew?

Our 80-year-old, 400-foot privet hedge has 3 plants with branches covered in white powdery substance. Leaves seem unaffected. What is this and how do we treat it?

Two Likely Culprits

1. Scale Insects (Cottony Scale or Mealybugs)

Test: Touch the white material. If it moves or you see tiny crawlers, it's insects. Look for sticky honeydew on leaves below.

• Cottony scale: White, cottony egg sacs on branches
• Mealybugs: White, waxy insects in branch crotches

Treatment: Systemic soil drench with imidacloprid (Bayer Advanced Tree & Shrub). Roots absorb it, kills sap-feeders within weeks. Provides 1-year protection. Avoid foliar sprays—they kill beneficials and miss protected insects.

2. Powdery Mildew (Fungus)

Test: White material doesn't move, wipes off, on leaves and stems. Favored by humidity, shade, poor air flow.

Treatment: Fungicide spray program:

• Start at first sign
• Spray every 7–14 days (more in cool, damp weather)
• Cover both leaf surfaces
• Products: Propiconazole, myclobutanil, triforine, sulfur, copper

Critical First Step: Identify Correctly

Misdiagnosis wastes time and money. Touch it. Watch for movement. Check for stickiness. Then treat accordingly.

For an 80-year-old hedge, systemic insecticide for scale is the safer, more effective bet if insects are confirmed. Powdery mildew on woody stems only is less common.