Daniel Gill | 4/18/2015 12:16:03 AM
Beautiful oaks of various species are an important part of Louisiana’s urban forests. Oak leaf blister, a disease caused by the Taphrina caerulescens fungus, attacks most species of oak found in Louisiana.
Species vary in susceptibility, but the southern red oak and water oak are two of the most severely affected. These species may be partially defoliated when conditions are favorable for disease development. Cool wet springs as the trees are leafing out provide those favorable conditions. Live oaks are generally not severely affected.
Blisters first appear on new leaves as gray areas on the underside and yellow or pale green spots on the upper side. Soon a blister forms on the upper surface of the leaf. The blistered areas may run together, causing the entire leaf to curl. Later, in early summer, the blisters turn brown and many infected leaves fall off the tree while those that remain are unattractive.
By the time you see the symptoms, there is nothing to be done. The disease has already infected the leaves at that point. Fortunately, oak leaf blister is not life threatening. The dropping leaves are messy and a nuisance, but there are no long term detrimental effects.
This disease occurs some years and doesn’t occur other years, so preventative spraying is generally not done. But, trees that have had heavy infections for two or more years may benefit by preventive sprays.
When control is warranted, the fungicide is sprayed over the entire tree just as the buds begin to swell. Make a second application about 2 weeks later. Mancozeb and chlorothalonil are recommended by the LSU AgCenter to treat oak leaf blister. If the tree is large, you will need to have this done professionally.
The LSU AgCenter and the LSU College of Agriculture