When is the best time to apply a fungicide to control oak leaf blister?

Applying a fungicide to control oak leaf blister is most effective when the buds are forming in the spring. This timing is crucial because the fungus that causes oak leaf blister primarily infects young, developing leaves. By targeting this specific phase of the plant's growth, the fungicide can effectively protect the foliage as it emerges, reducing the incidence of infection and subsequent damage.

Other timings, such as after leaf drop or in the fall, would be less effective because the disease is not actively impacting the tree during those periods when the leaves are no longer present or when the tree is preparing for dormancy. Similarly, applying fungicides too late in the spring, once the leaves are fully formed, may not yield effective results. Therefore, treating while the buds are forming allows the fungicide to work at the most crucial time for preventing disease establishment.