Issue 5, June 17, 2021
Oak Leaf Blister
I have lived in my current home for several years. Every year, except for one abnormally dry spring, I’ve watched oak leaf blister infection develop on my black oak. I often use my tree as an example of how weather can influence disease pressure.
Oak leaf blister is a common foliar disease caused by the fungal pathogen, Taphrina caerulescens. Although all oaks are susceptible, red and black oaks are among the most affected by this foliar disease. White oaks are rarely infected.
Symptoms begin as circular, raised spots on the upper surface of the leaf, as seen in the pictures. As the symptoms continue to develop, they become more distinct and appear as scattered blister-like, puckered, or raised areas on the leaves. Symptomatic tissues are often thickened and have a light green color, which transitions to reddish-brown as the season progresses. Severely diseased leaves may drop prematurely.
Oak leaf blister on black oak, June 2021. Travis Cleveland, University of Illinois
The pathogen survives over the winter on twigs and between bud scales. Infection occurs early in the spring during cool, moist weather, as the buds start to swell and open. Expanded leaves are not susceptible. Damage to trees in Illinois is primarily aesthetic, and the disease is generally not considered to be a significant landscape problem. Management should focus on promoting oak tree vigor through pruning, watering, and fertilization. Though not usually warranted or recommended, several fungicides are labeled to control oak leaf blister. These products are only effective if applied as a dormant application to buds and twigs.
Author:
Travis Cleveland