What is Oak Leaf Blister?

Oak Leaf Blister is a fungal disease that affects oak trees. It causes raised, circular or angular areas on leaves that are initially light green or yellow and eventually turn brown or black. The affected leaves may drop prematurely, and the disease can lead to defoliation and reduced tree vigor.

Oak Leaf Blister is generally not a serious disease but primarily an aesthetic concern. Although it can cause some defoliation, trees are not usually killed by the disease. However, repeated infections over time can weaken the tree, making it more susceptible to other diseases and pests. Therefore, it is important to take preventative measures to reduce the incidence and severity of Oak Leaf Blister on affected trees.

What are the Symptoms?

Symptoms of oak leaf blister may include:

• Small raised blisters on the upper surface of the leaves.
• Blisters that are yellow or light green when young and turn brown as they age.
• A puckered or distorted appearance of the affected leaves.
• Premature defoliation, or the shedding of infected leaves.

If Oak Leaf Blister happens in late summer, it may not have any significant impact on the tree, as the leaves are nearing the end of their lifespan anyway. However, if the disease occurs earlier in the season, it can cause significant leaf drop and early defoliation, which can weaken the tree and leave it more susceptible to other diseases and pests.

What Causes Oak Leaf Blister?

Oak Leaf Blister is caused by a fungal pathogen called Taphrina caerulescens. This pathogen infects the leaves of oak trees and causes circular or irregular raised blisters on the upper surface of the leaf. 

How to Prevent Oak Leaf Blister?

Here are some tips for preventing oak leaf blister:

• Provide adequate moisture to trees during dry periods, but avoid over-watering.
• Avoid fertilizing oak trees with high levels of nitrogen, which can promote succulent new growth that is more susceptible to the disease.
• Rake up and dispose of fallen leaves to reduce the amount of fungal inoculum on the ground.
• Prune out infected branches and twigs as soon as symptoms are noticed, making sure to disinfect pruning tools between cuts to avoid spreading the disease.
• Use fungicides according to label instructions to protect susceptible trees during periods of high disease pressure.

By following these practices, you can help prevent oak leaf blister from affecting your trees.