Timing is crucial when it comes to trimming your trees and shrubs. Oak and Elm trees in Iowa should be trimmed sometime during the dormant season to prevent the spread of fungal infection through fresh wounds. Insects are also known to aid in transmitting the pathogens that cause Oak Wilt and Dutch Elm Disease. Trimming out dead wood before the growing season begins will help the tree come out of dormancy with the most natural resistance it can have to infestation. In addition, the tree will have the entire growing season to begin sealing around the cuts in the process known as CODIT (Compartmentalization of Decay in Trees) in which the tree produces callus tissue to protect itself from insects, disease and deterioration. When Oak and Elm trees must be trimmed in the summer for any reason, such as mitigating emergency storm damage, we apply wound dressing called pruning seal. As we move into Spring we can trim fruit trees, bushes and evergreens thoughout the season according to custmor's needs, but should consider not pruning some sensitive species of each as we get closer to Fall.