Apple Scab

Plants Affected:

Images of This Plant Disease:

Images of leaves from an apple tree with a case of apple scab

Leaves from an apple tree with a case of apple scab

Image of a branch of an apple tree with a case of apple scab

Branch of an apple tree with a case of apple scab

Image of apples from a tree with a case of apple scab

Apples from a tree with a case of apple scab

 

Overview

Apple scab is the most common disease of crabapple in Iowa, but can also be found on many varieties of apple and pear.

Signs and Symptoms

The causal fungus causes spots on leaves. In early stages, spots appear as small black or olive-green, velvety lesions with irregular margins. Later the spots become more distinct and may grow up to one-half inch in diameter. Infected leaves eventually turn yellow and fall prematurely. Infected fruit show distinct brown or black spots with margins that are often irregular. When severe, the skin splits open and irregularly shaped fruit results.

Disease Cycle

Apple scab is caused by the fungus Venturia inaequalis. This fungus survives the winter in infected leaves on the ground. In the spring, the fungus produces sexual spores (

Types of Samples Needed for Diagnosis and Confirmation

Collect 3 to 5 twigs with leaves attached and fruits. For further information go to Fruits

Management

Cultural methods of disease management produce better results in relatively dry years and, in some situations, may even eliminate the need for fungicides. A properly pruned open tree canopy has better ventilation which allows for faster drying of leaves, reducing the number of infections. Because the apple scab fungus

Selection of high quality, disease resistant varieties is desirable since there are differences in susceptibility. However, since crabapple

There are fungicides labeled for the control of apple scab. Spray scab-susceptible