Artemisia princeps

Fungal disease affecting apple trees

Apple scab is a fungal disease caused by the pathogen Venturia inaequalis. It is one of the most common and economically significant diseases affecting apple trees worldwide. The disease primarily affects the leaves, fruit, and sometimes the young twigs of apple trees, leading to reduced fruit quality and yield.

Symptoms

The first symptoms of apple scab appear in early spring as olive-green spots on the leaves. These spots gradually darken and become velvety in texture. As the disease progresses, the spots may coalesce, causing the leaves to become distorted and eventually fall off. On the fruit, scab lesions appear as dark, sunken areas that can crack and deform the apple, making it unmarketable.

Life Cycle

Apple scab is a polycyclic disease, meaning it can produce multiple infection cycles within a single growing season. The fungus overwinters in fallen leaves and infected twigs. In the spring, as temperatures rise, the fungus produces spores that are released into the air and carried by wind to infect new leaves and fruit. Moisture from rain or dew is necessary for the spores to germinate and infect the host plant.

Management

Effective management of apple scab involves a combination of cultural practices, resistant cultivars, and fungicide applications. Cultural practices include removing and destroying fallen leaves to reduce the source of overwintering inoculum. Planting scab-resistant apple varieties can also significantly reduce the incidence of the disease. Fungicides are often applied preventatively, starting at bud break and continuing throughout the growing season, especially during wet weather conditions.

Impact

Apple scab can cause significant economic losses in commercial apple production due to reduced fruit quality and yield. The disease can also increase production costs due to the need for frequent fungicide applications. In addition to its economic impact, apple scab can affect the aesthetic quality of apples, making them less appealing to consumers.

Related pages

• Apple
• Fungal plant pathogens
• Plant disease management

Gallery

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  Apple fruits affected by scab
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  Close-up of apple scab lesions
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  Scanning electron micrograph of apple scab