Diagnostic Guide
What are the sticky spots or cottony bumps on my plant?
Check leaf joints and stems closely for cottony clusters or small bumps before assuming it's dirt or damage.
Last reviewed: August 6, 2026 · Sources: University of California IPM
Start with the visible pattern
| What you see | Most likely cause | Check first |
|---|---|---|
| Cottony white masses in leaf joints | Mealybugs | Check leaf joints and the undersides of leaves |
| Small waxy brown bumps on stems that don't rub off | Scale | Inspect stems closely for raised bumps |
Look closely at leaf joints and along stems. Cottony clusters that don't rub off easily, or small brown waxy bumps, confirm mealybugs or scale rather than dirt or disease.
Simple checks before you buy anything
Most garden problems have more than one possible cause. Start with the simplest explanation.
- Isolate the plant from others while you confirm and treat.
- Wipe visible pests off with a cotton swab dipped in rubbing alcohol before spraying anything.
- Check new plants closely before placing them near this one, since this is a common way infestations spread.
Most likely causes to check first
Mealybugs or scale
Confidence: 85%Mealybugs show up as cottony white masses in leaf joints, and scale looks like small waxy brown bumps stuck to stems and leaves. Both feed on sap and leave a sticky residue behind.
- Look closely at leaf joints and stems for cottony white clusters or small brown bumps that don't rub off easily.
- Check nearby surfaces for a sticky, shiny residue the pests leave behind.
- Inspect new plants closely before placing them near others, since this is a common way infestations spread.
Reference material used on this page
University of California IPM
Powdery mildew identification and control
Publication date: 2025
Visit sourceGet the free GardenMD Quick Reference Guide
A printable symptom cheat sheet and seed starting calendar, sent straight to your inbox.
No spam. Unsubscribe anytime.