Along with blue spruce trees, the number one tree I have been getting calls about looking sick or dying are oak trees. Typically these oak trees are very old, original to the landscape, and have been slowly declining over the past few years. There are a number of reasons why this might be happening, but the number one reason is still environmental factors.
Trees are massive specimens, and sometimes injuries or stress from weather events take years to show up as noticeable symptoms. For example, trees that were severely affected by the drought in 2012 may not have shown any decline until a few years afterwards. Additionally, what stresses trees out the most, particularly older trees, is large fluctuations in weather, which we have had plenty of the past few years. Dry seasons, followed by extremely wet spells; mild winters one year, followed by extreme temperatures the next, is asking a lot for trees to adapt to, and older trees that are already susceptible to problems simply cannot adapt quickly enough. About the only thing you can do to trees in this state is try and keep the trees as stress free as possible, which basically comes down to making sure they are getting water during dry periods.
While the environment can be accounted for most oak tree decline, there are other pests that may be contributing to issues, particularly for red and black oak trees. Oak wilt is a fatal disease of oak trees in Indiana and around the Midwest. Oak wilt is caused by a fungus that permeates the trees vascular system and plugs the trees water conducting vessels. This disrupts the flow of water and nutrients, causing the oak to wilt, drop leaves, and die back. The fungus can be spread by sap feeding beetles and contaminated pruning tools.
Symptoms of oak wilt include: bronze or tan colored tan tissue that begins at the leaf tips and moves towards the leaf base, which often remains green; leaf drop usually occurring in June; dark streaks beneath the bark on the sapwood surface; and a nearly completely defoliated tree by late summer. If you have an infected oak tree, it may be necessary to remove the tree so that the disease does not spread. To prevent the spread to other trees, try to prevent wounds to the tree, and treat tree wounds if they do occur. Also, always sanitize your tools after pruning trees.
If your tree has some of the symptoms described above, do not panic, as there are other similar disorders that the tree can recover from so it is important to properly diagnose the problem before action is taken. Root stresses, for example, caused by soil compaction, root restriction, and drought will look similar. To confidently diagnose the issue, you may consider sending a sample to the Purdue Plant and Pest Diagnosis Lab (PPDL) for testing. If collecting a sample is an issue due to the size of the tree, you may want to consult a certified arborist to help, who can be found by visiting the website: www.treesaregood.org/findanarborist For more information on oak wilt, including pictures of symptoms as well as how to collect and send a sample to the PPDL, I would recommend reading the following publication: https://www.extension.purdue.edu/extmedia/BP/BP-28-w.pdf