Diagnosing Gummosis in Cherry Trees: Beyond the Borer Myth

Diagnosing Gummosis in Cherry Trees: Beyond the Borer Myth

Gum bleeding (gummosis) on cherry trees is often blamed on peachtree borers, but the causes are diverse. Written by Bob Stewart, Area Extension Educator.

Peachtree Borer vs. Other Causes

• Borer: Gum low on trunk (≤1 ft), mixed with frass (sawdust), emerging from a distinct exit hole.
• Mechanical Injury: Gum at wound site from mowers, trimmers, hatchets, etc. No frass.
• Infectious Cankers: Three pathogen groups cause cankers leading to gummosis:
  • Pseudomonas bacteria → bacterial canker (more liquid).
  • Leucostoma (Cytospora) fungus → Leucostoma canker.
  • Botryosphaeria dothidea fungus → fungal gummosis.

Diagnosing Cankers

A canker is a necrotic, often sunken lesion. Scrape away gum; if bark is loose and underlying tissue is discolored/dead, it's a canker. Bark may slough off easily.

Stress Connection

Cankers typically invade trees under environmental stress—weak roots from poor soil or drought. Cherry trees stress easily, opening the door to infection.

Key Takeaway

Don't assume borers. Examine closely: distinguish insect damage, mechanical injury, and infectious disease. Accurate diagnosis leads to appropriate action.