Brown-black spots that enlarge to
become more or less circular giving
a "scab" appearance.

Apple Scab

Plants Affected

Fruit apple, crabapple, several species of mountain ash, pyracantha, cotoneaster, common pear.

Symptoms/Damage

Leaves

Small olive green infection spots on leaves that enlarge to become more or less circular. Leaves can be curled or puckered. Defoliation or leaf drop occurs, weakening the tree.

Fruit

Brown-black spots that enlarge to become more or less circular rendering the fruit unmarketable. Points of infection will become raised to give a scab appearance.

Twigs

On young succulent growth, bumps will occur and with time become cracked and rough.

Life Cycle

Infection can take place two different ways. Overwintering spores on twig infections can be responsible for initial infection in spring, particularly following a severe scab year. Most infections; however, are initiated by airborne spores that overwinter on fallen leaves and fruit from the previous season.

In the spring, spores are released into the air for about three months, which go on to infect fruit and foliage buds, and newly developing leaves and flowers. Infection can only take place when the plant is wet. The longer plant parts are wet, the more severe the infection. In addition, the warmer the temperature is, the quicker an infection can take place. Our rainy weather in the Northwest provides an ideal environment for severe apple scab infections.

Management

Cultural

 Plant resistant fruit apple cultivars like Liberty, Akane. Or Plant ornamental crab apple varieties like prairie fire or golden rain drops

 Remove leaves after they fall throughout the season and destroy.

 Prune plant to increase airflow and reduce wetness time from rain and dew.

 Avoid overhead watering

Chemical

 An approved fungicide application at 2-3 week intervals starting at bud break until dry weather.