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Another installment in our series of posts where Texas Tree Surgeons answers your tree questions. Are you having problems with your trees and want to know what’s wrong? Let us know!

The leaves on our oak trees are looking diseased, with bumps all over them. Is this oak wilt?

Oaks are the most common trees in our North Texas urban forest, and they can suffer from many different health issues. If your oak is showing misshapen leaves with bright green bulges on them, it is most likely a fungal disease that may look bad, but is not usually harmful to the overall health of the tree.

Oak Leaf Blister 

  • Oak leaf blister is caused by the fungus Taphrina caerulescens, which enters the new leaf buds during cool and moist spring weather.
  • The fungus causes the young leaves to develop blister-like bumps on their surfaces, with coloration ranging from light green to brown.
    • In more severe cases, the leaves may fall off altogether.
    • The fungus does not affect mature leaves, only new growth.
  • Like other fungal diseases, oak leaf blister is more prevalent during periods of cooler weather with increased rainfall in the spring, and cannot survive the summer heat.

Does Oak Leaf Blister Kill the Tree?

Oak leaf blister and the T. caerulescens fungus do not pose a serious risk to the health of affected trees.

Can Oak Leaf Blister Be Treated?

  • The spores which carry the oak leaf blister fungus are present on the bud sites over the winter, and once the tree begins showing infected leaves, chemical treatment is not effective.
    • It is possible to apply a preventative fungicide, but this must be done before bud break and while the young leaves are maturing.
  • If you have a tree with oak leaf blister, the best course of action is to clean up fallen infected leaves and dispose of them in plastic bags.
    • Do not place leaves in compost, as this may encourage further fungal growth.
  • Keeping a tree healthy with proper mulching and fertilization, as well as maintaining soil drainage, will help it resist future health issues.

At Texas Tree Surgeons, we love trees and we love our customers! While oak leaf blister can be unsightly, it is mostly harmless and is not a serious concern to the health of the tree. Of course, there are many oak health issues that can cause long-term damage and tree death. Oak wilt is a major concern. Trimming oaks should be avoided between February and July if possible, and proper precautions taken if trimming cannot be postponed. Oak decline is also a problem, especially in areas where many of the trees were planted around the same time, and are reaching the end of their lifespan. If you have any questions about the health of your oaks, or any other tree care issues, let us know!