Brown Spots on Orchid Leaves: Scale Insect or Fungus?

Diagnosing Brown Leaf Spots

You've had your orchid for a year and notice small brown spots on otherwise firm, green leaves. Before treating, you need to identify the cause—two common possibilities are brown scale insects or a fungal infection.

Simple Diagnostic Test

1. Soak a cotton swab in 70% isopropyl (rubbing) alcohol.
2. Gently rub a few spots.
3. If spots wipe off: Likely brown scale (a sucking insect). The alcohol dissolves their protective covering.
4. If spots remain: Probably a fungal or bacterial leaf spot.

Next Steps

For scale: Wipe all visible insects off leaves and stems with alcohol-soaked swabs or a soft cloth. Repeat weekly for 3–4 weeks to catch hatchlings. For heavy infestations, use a systemic insecticide labeled for orchids.

For fungus: Improve air circulation, water only in the morning, and avoid wetting leaves. Apply a copper-based fungicide or neem oil per label directions. Remove severely affected leaves.

Prevention

• Inspect new plants thoroughly before introducing them.
• Space plants for good airflow.
• Water early in the day so foliage dries quickly.
• Repot annually in fresh mix to prevent root issues that weaken the plant.

Do the alcohol test and report back for specific treatment advice.