Wax Scale on Boxwood: Identification and Treatment Timing

Those white, rounded bumps on your boxwood stems with blood-red undersides are almost certainly wax scale (Ceroplastes spp.). Adult females protect themselves with a thick, white waxy coating while feeding on plant sap. Their bright red eggs develop beneath this shield.

Immediate Action: Physical Removal

If the infestation is light, scrape or brush off all visible adults. This reduces the egg load significantly. However, tiny crawlers (newly hatched nymphs) are well-camouflaged on stems and easily missed.

Why Timing Matters

Horticultural oil applied in winter has limited effect because the insects are inactive. The critical window is mid-April, when crawlers emerge from beneath the dead females. This is when they're most vulnerable—no waxy armor yet, actively moving to new feeding sites.

Recommended Treatment Schedule

1. Mid-April: Apply carbaryl (Sevin) or horticultural oil at crawler emergence.
2. Two weeks later: Second application.
3. Two weeks after that: Third application.

Thorough coverage of stems and leaf undersides is essential. Use a sprayer that reaches into the plant's interior.

Long-Term Prevention

• Prune for better air circulation and spray penetration.
• Monitor annually in early April for crawler activity (tap a branch over white paper).
• Avoid excessive nitrogen fertilizer, which promotes succulent growth that scale favor.

Your boxwoods are historically significant—consistent, well-timed treatment will protect them for years to come.