Diagnosing Black Dots and Resin on Young Tree Leaves

Mystery Symptoms: Black Dots and Sticky Resin

Small black dots on leaves accompanied by a resinous substance suggest several possibilities, but accurate identification requires visual confirmation. The description points toward either an insect infestation or a fungal issue with secondary symptoms.

Likely Culprits

• Scale insects: Many species appear as small, immobile bumps (black, brown, or white) on leaves and stems. They excrete honeydew—a sticky, resin-like substance that can foster sooty mold.
• Aphid colonies: Dense aggregations can look like black dots; their honeydew creates the sticky residue.
• Fungal fruiting bodies: Some leaf spot fungi produce dark reproductive structures (pycnidia or acervuli) visible as tiny black dots. The "resin" might be plant sap exuding from damaged tissue.
• Insect frass (droppings): Caterpillars or beetles feeding on leaves leave dark granular waste.

Next Steps for Diagnosis

1. Take clear, close-up photos of the affected areas—both the dots and the resinous substance. Ensure images are in focus by reviewing on a computer before sending.
2. Examine leaf undersides and stems for mobile insects, cottony masses, or armored bumps.
3. Check for sooty mold: A black, powdery coating on the sticky residue confirms honeydew presence, pointing to sap-sucking insects.
4. Submit samples or photos to your local cooperative extension office or a certified arborist for definitive identification.

General First Aid While Awaiting ID

• Prune and destroy severely affected foliage.
• Improve air circulation around the tree.
• Avoid overhead watering to reduce fungal spread.
• Do not apply broad-spectrum insecticides until the pest is confirmed—beneficial insects may be present.

A photo submission will allow for precise diagnosis and targeted treatment recommendations.