What is Apple Scab?

Apple scab is a fungal disease that affects apple trees, causing dark spots on the leaves and fruit. It can lead to reduced fruit production and premature leaf drop. The disease is caused by the fungus Venturia inaequalis and is most common in areas with cool, wet springs.

Good cultural practices such as pruning and sanitation can help prevent and manage the disease, and fungicides can also be used.

What are the Symptoms?

On leaves: 

• Appearance of small, circular, and olive-green spots on the leaves.
• As the disease progresses, the spots turn into larger, darker lesions with raised borders.
• The leaves may also become distorted, curled, and yellowed.
• In severe cases, the leaves may drop prematurely, leading to the defoliation of the tree.
• Infected leaves may also develop a velvety texture due to the presence of fungal spores.

On Fruits:

• Scab-like lesions on the fruit surface that become raised and dark over time
• Fruits are often misshapen and may crack or split due to the scab infection
• Severely infected fruits may rot and drop from the tree prematurely, leading to yield loss
• As the disease progresses, the infected fruits become increasingly disfigured, with the scab lesions merging to form large, rough areas on the fruit surface.

It is important to note that early-season apple scab infections on leaves can lead to fruit scab infections, as spores produced on infected leaves can be transported to the fruit.

On Twigs:

• Cankers or sunken areas on the bark of the twig, which may ooze sap.
• Twigs may become deformed or stunted.
• The bark on affected twigs may crack and peel away.
• The twig may die back and drop leaves early.
• Twig infections can also cause the leaves and fruit on the same branch to become infected with apple scab.

How to Control Apple Scab?

Apple scab can be controlled through a combination of cultural practices and chemical treatments. Here are some methods for controlling apple scab:

• Keep the area around the apple tree free of fallen leaves and debris.
• Prune the apple tree to improve air circulation and sun exposure.
• Plant resistant apple tree varieties if possible.
• Apply fungicides according to their label instructions before the apple tree leafs out and again after petal fall.
• Consider using biological control methods such as beneficial fungi and bacteria.
• It is important to note that prevention is key when it comes to apple scab. Regular maintenance and a proactive approach can help to prevent the spread of this fungal disease.