Oak trees (Quercus spp.) are often some of the most prized trees in a homeowners yard. Knowing when and how to prune oaks when hiring a contractor or taking on a DIY project is important with respect to tree vigor, longevity, and structural integrity. One of the most common mistakes is pruning oaks between Mid-March thru June. This can lead to an agressive pathogenic infection known as 'Oak Wilt'. Pruning cuts during this time of year can lead to the infection of trees which then is spread to adjacent oak trees via root grafted root systems. Below is an article that outlines signs, symptoms, and other information about oak wilt. Consulting with an arborist is always recommended before pruning your oak trees.