Disease Directory

    Tar Spot

    Rhytisma acerinum, Rhytisma punctatum

    Fungus
    Leaves

    Overview

    A fungal disease primarily affecting maples, causing raised, shiny black spots on leaves that resemble drops of tar. Generally cosmetic but can cause premature leaf drop in severe cases.

    Symptoms

    Raised, thick, shiny black spots (1-2 cm) on upper leaf surfaces resembling tar drops. Yellow halos may surround spots. Heavy infections cause premature leaf drop in late summer.

    Environmental Conditions

    Humid

    Prevention

    Rake and destroy fallen leaves in autumn to reduce inoculum. Improve air circulation. Generally does not require chemical control.

    Management

    Rake and compost or destroy fallen leaves. Fungicide application is rarely warranted. Maintain tree vigor through proper watering and fertilization.