Plant Problem Diagnostic
Scale Insects: How to Identify and Manage Them
The short answer
Scale insects are small, immobile bumps that attach to stems, leaves, and branches. Soft scales secrete sticky honeydew that leads to black sooty mold; armored (hard) scales have a shell-like cover that lifts off the insect and do not produce honeydew. Because the adults are protected under a waxy shell, the least-toxic control targets the mobile 'crawler' stage: horticultural oil gives thorough coverage of stems and both leaf surfaces and smothers young scales.
For light infestations, prune out and destroy the most heavily encrusted twigs, and gently rub scales off small indoor plants. Dormant oil applications in winter can reduce scales on trunks and branches of woody plants. If a valued plant is heavily infested or you cannot tell soft from armored scale, consult your local Extension office, since the two groups respond differently to treatment.
How to identify scale insects
Scales resemble raised bumps or scabs that do not brush off easily. Soft scale infestations show honeydew and sooty mold; armored scales have a separate cover you can flick off to reveal the insect beneath.
- Small circular or oval bumps on stems and leaf undersides
- Soft scale: sticky honeydew and black sooty mold present
- Armored scale: dry, shell-like cover, no honeydew
Least-toxic management, in order
- 1Prune and remove — Cut out and destroy heavily infested twigs and rub scales off small indoor plants.
- 2Target crawlers with oil — Apply horticultural oil to coat all bark and leaf surfaces when the mobile crawler stage is active.
- 3Dormant oil on woody plants — A winter dormant-oil application can kill scales overwintering on trunks and branches.
- 4Conserve natural enemies — Parasitic wasps and predators often keep scale in check; avoid broad-spectrum sprays that kill them.
When to escalate
Heavy, recurring scale on trees and shrubs may need professionally timed treatment. Because control depends on correctly separating soft from armored scale, send a sample to your regional Extension diagnostic lab if you are unsure before escalating beyond oil.
⚠ Some systemic insecticides do not control armored scales even though they affect soft scales. Confirm which scale you have before choosing any product.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Maryland Extension — Introduction to Scale Insects — Difference between soft and armored scales, honeydew, and identification cues
- Clemson Home & Garden Information Center — Armored Scale Insects — Targeting the crawler stage with horticultural oil, dormant oil, and that systemic imidacloprid does not kill armored scales