What are the orange spots on your apple tree leaves?

Orange spots on apple tree leaves are often a sign of a fungal disease called apple scab. Apple scab is caused by the fungus Venturia inaequalis, which overwinters in fallen leaves and can infect apple trees in the spring when temperatures are cool and wet. The fungus produces spores that are spread by wind and rain, and can infect leaves, fruit, and twigs of apple trees.

Apple scab first appears as small, pale green spots on the leaves, which gradually turn yellow or orange-brown as the disease progresses. The spots may also have a velvety or powdery appearance, and can merge together to form large, scab-like lesions.

In severe cases, apple scab can cause defoliation and can also affect the fruit, causing it to become misshapen and blemished.

To prevent apple scab, it is important to keep the orchard floor free of fallen leaves, which can harbor the fungus over the winter. Pruning trees to improve air circulation and reduce humidity can also help to reduce the risk of infection. Fungicides may be necessary to control apple scab, especially in areas where the disease is known to be a problem.