Sooty Mold on Indoor Lemon: Scale Insects, Honeydew, and Cleaning Up

What You're Seeing

Colorless gluey substance on leaves + black sticky dust on floor = sooty mold growing on honeydew from scale insects or mealybugs.

Find the Source

• Inspect leaf undersides: small (5 mm) circular/oval bumps = adult scale.
• Juvenile scale: tiny, fuzzy, mobile.
• Mealybugs: cottony tufts at leaf-stem junction.

Treatment

• Insecticidal soap for juveniles and mealybugs.
• Sponge with soap to physically remove adults (light pressure).
• This also cleans the sooty mold.

Note

Sooty mold doesn't directly harm the plant, but heavy coatings reduce photosynthesis. Control the insects, and the mold disappears.

UK Products

Check local garden centre for available insecticidal soaps.