Dying Poplar Trees: Cytospora Canker Diagnosis and Management

Poplar Decline Over Four Years

Ten poplars reduced to eight; trunks turn orange, leaves brown, trees die without leaf drop. Owner in unknown location, moved in four years ago.

Diagnosis: Cytospora Canker

Caused by fungus Cytospora chrysosperma (sexual stage Valsa sordida). Affects weakened poplars, aspens, willows. Enters through wounds, kills twigs back to larger branches. Forms sunken, brownish cankers; inner bark blackens, smells foul. Trees 3–6 inches diameter die in 2–3 years. Spores spread by rain, wind, birds, insects.

Management Options

• Bordeaux Mixture: Copper-based fungicide for prevention. Recipe: UC IPM Bordeaux Guide.
• Improve Vigor: Adequate water, avoid wounds, fertilize appropriately.
• Remove Dead Wood: Prune infected branches back to healthy wood; sterilize tools.

Note

Cankers attack stressed trees. Address underlying stressors (drought, poor soil, damage).