Pear scab is a fungal disease caused by the pathogen Venturia pirina. It affects pear 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 become distorted or twisted.
   • Severely infected leaves may drop prematurely.
2. Fruit Symptoms:
   • Rough, scabby lesions on the fruit surface.
   • Lesions may be dark brown to black in color and may have a velvety appearance.
   • Severely infected fruit may crack or become deformed.
   • Fruit may become misshapen or stunted in growth.
3. Twig and Stem Symptoms:
   • Scabby lesions may develop on twigs and stems, leading to cankers.

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 pear scab. Consult with local agricultural extension services for recommended fungicides and application schedules.
3. Resistant Varieties:
   • Planting pear varieties that are resistant to pear scab can greatly reduce the incidence and severity of the disease.

Causes:

1. Fungal Pathogen: Pear scab is primarily caused by the fungus Venturia pirina.
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 pear varieties known to be resistant to pear scab to reduce the need for chemical control.

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