Pale, yellow eruptions are caused by a fungus which infects the leaf as it is emerging from the bud and expanding in the spring. The fungus is present at low levels in oaks every year. In some years, when spring rains come at just the right time, a large number of infestations can occur and the foliage may be noticeably disfigured. Since we cannot predict the “bad” years, and since injury to the tree is usually slight or of no consequence, control of leaf blister is not recommended.
Cooperative Extension Ventura County
Oak Leaf Blister
Pale, yellow eruptions are caused by a fungus which infects the leaf as it is emerging from the bud and expanding in the spring. The fungus is present at low levels in oaks every year. In some years, when spring rains come at just the right time, a large number of infestations can occur and the foliage may be noticeably disfigured. Since we cannot predict the “bad” years, and since injury to the tree is usually slight or of no consequence, control of leaf blister is not recommended.