Apple scab is a fungal disease caused by the pathogen Venturia inaequalis. It affects apple trees and can lead to significant damage to both leaves and fruit. Here’s an overview of its symptoms, recommendations, causes, and preventive measures:

Symptoms:

1. Leaf Symptoms:
   • Olive-green to black lesions on leaves.
   • Initially small, circular spots that enlarge and may merge.
   • Infected leaves may curl or become distorted.
   • Severely infected leaves may drop prematurely.
2. Fruit Symptoms:
   • Rough, dark patches on the fruit surface.
   • Lesions may crack or become sunken.
   • Severely infected fruit may be deformed or even drop prematurely.
3. Twig and Stem Symptoms:
   • Scabby lesions may develop on twigs and stems.

Recommendations:

1. Cultural Practices:
   • Prune trees to increase air circulation, which helps to reduce humidity and minimize disease spread.
   • Remove and destroy infected leaves, fruit, and prunings to reduce inoculum for the next season.
2. Chemical Control:
   • Fungicides can be applied preventively to protect against apple scab. Consult with local agricultural extension services for recommended fungicides and application schedules.
3. Resistant Varieties:
   • Planting apple varieties that are resistant to apple scab can greatly reduce the incidence and severity of the disease.

Causes:

1. Fungal Pathogen: Apple scab is primarily caused by the fungus Venturia inaequalis.
2. Environmental Conditions: The disease thrives in conditions of high humidity and moderate temperatures, typically between 60°F to 75°F (15°C to 24°C), with rainfall or overhead irrigation providing moisture for spore dispersal.

Preventive Measures:

1. Site Selection: Choose planting sites with good air circulation and sunlight exposure to minimize humidity and promote drying of foliage.
2. Sanitation: Regularly remove and destroy fallen leaves and fruit, as they can harbor fungal spores overwinter.
3. Fungicidal Sprays: Apply fungicides according to a recommended schedule, especially during periods of wet weather when infection is most likely.
4. Resistant Cultivars: Consider planting apple varieties known to be resistant to apple scab to reduce the need for chemical control.

By combining cultural practices, chemical control when necessary, and selecting resistant varieties, apple growers can effectively manage and mitigate the impact of apple scab on their orchards. Regular monitoring and prompt action are key to successful disease management.