Maple Tar Spot: Spore Timing and Management

A maple diagnosed with tar spot raises questions about reinfection cycles and fungicide use on fallen leaves.

Key Facts

• Spring ascospores (sexual spores) are infectious; produced on overwintered leaves.
• Summer conidia (asexual spores) are not infectious to new leaves.
• Rake and destroy fallen leaves before spring to break the cycle.
• Spraying fungicide on ground/grass is not useful.
• Tree spraying requires precise timing and full coverage—difficult on large maples.

Practical Advice

Focus on sanitation: thorough fall leaf removal. Fungicide on the tree is rarely warranted for this cosmetic disease.

Expert insight provided by Steve.