Plum Tree Amber Sap: Gummosis Causes and Diagnosis

Sticky Amber Sap Oozing from Plum Trunk

What causes plum tree to ooze amber sap?

Gummosis: Symptom, Not Disease

Sap exudation from bark break. Causes:

• Peachtree Borer: Low on trunk (<1 ft), frass (wood debris) in gum.
• Mechanical Injury: Hatchet, mower, pruning wounds.
• Canker Diseases: Bacterial (Pseudomonas), fungal (Leucostoma/Cytospora, Botryosphaeria). Key: canker = dead tissue under gum, bark loose/discolored.

Stress Connection

Cankers invade stressed trees (drought, poor planting, overwatering). Cherry/plum stress easily.

Diagnosis

Scrape gum, probe bark. Dead tissue = canker. No frass + high up = not borer.