Tar Spot on Silver Maple: Management and Perspective

2008-planted silver maple sapling has black "tar spots" on leaves. Cause and cure?

Cause: Rhytisma Fungi

• Overwinter on fallen infected leaves.
• Spring: spores release, infect new leaves.
• Raised black spots = fungal fruiting bodies.

Impact

• Rarely threatens tree health.
• Heavy infection → early leaf drop (raking nuisance).
• No long-term damage per research.

Management

1. Rake/destroy leaves in fall—reduces spores.
2. Mulch leaves (cover/turn pile before spring).
3. Fungicides (mancozeb, triadimefon, copper) only if unacceptable—difficult on mature trees.

Bonus

Fertilize: 10-10-10 at 1 lb/inch trunk diameter to offset leaf loss.