Extensive leap drop from oak tree

Question: Good Afternoon, My question is regarding a large oak tree ( I think). It started dropping leaves a couple months ago and now is very bare, starting from the bottom up. I am attaching pictures of the leaves, which seem to be mostly brown, with darker spots, as well as some that  still have some green. I also noticed a long split in the bark that may or may not be a recent development.We have not had the tree pruned or trimmed in the last 15 years. My questions are: what is your best guess of diagnosis and what are the next steps? I will be most grateful for your help. Thank you

responder: Thank you for your question!   Laura S.      Michigan State University Extension Advanced Master Gardener Volunteer You may also contact the toll free MSU Extension lawn and garden hotline at 1-888-678-3464 with your gardening questions or visit www.migarden.msu.edu for Smart Gardening resources. Replied August 20, 2024, 5:08 PM EDT
response: Hi Kathy, It would be helpful to also have a picture of the base of the trunk where it enters the soil, and a close up of a branch- from about 2 feet away. Thank you. Laura S.

responder: The Question Asker Replied August 20, 2024, 5:38 PM EDT
response: Hi Laura, I am attaching the pictures you requested but I can’t get up very close to the branches. Images also include the bark split.  On 08/20/2024 5:08 PM EDT Ask Extension wrote:

responder: Julie Crick  Replied August 21, 2024, 10:19 AM EDT
response: Hi Kathy, It may be best to call me so I can ask some questions regarding the leaf drop and the tree itself.<personal data hidden>. That said, I'll provide some information below.  First, oak wilt generally starts with leaves wilting and falling off from the top down. The tree dies within a few weeks. Because the top of the tree appears to still have leaves, I'm guessing this is not oak wilt.  The leaves that fell, and the leaves on the tree appear to be a lighter green than those on the neighboring trees. When leaves turn yellowish green, and remain green near the veins of the leaf, this is chlorosis. Chlorosis occurs when the soil pH is over 7.0 and the tree can not absorb macronutrients like iron and manganese, which are required for photosynthesis. The solution is to use a chemical approach to modify the pH of the soil near the base of the tree. Below is a publication that describes chlorosis, and how to treat it.  https://www.purdue.edu/fnr/extension/iron-chlorosis-of-trees-and-shrubs/ I'm not sure the crack in the bark has significance in this situation.   You asked about diagnosis reliability. If we are not sure about a recommendation, we will let you know. If you'd like someone to come to your house and physically examine the tree to determine the issue, you may reach out to a certified arborist. Arborists are certified through the International Society of Arboriculture, or ISA. They maintain a website that makes it easy to find a professional.  https://www.treesaregood.org/  Please feel free to reach out if you'd like via telephone or by replying to this email.   Thank you, -Julie

responder: The Question Asker Replied August 21, 2024, 1:00 PM EDT
response: Hi Julie, I’d like to thank you for your prompt and thorough response! I will read the information you  forwarded and possibly call you with my husband present to discuss the matter. In the meantime, if we were to chemically treat the tree for chlorosis, could that harm the tree? My main objective is to preserve this beautiful part of our landscape. Also, what type of oak tree is it? Thanks, Kathy  On 08/21/2024 10:19 AM EDT Ask Extension wrote:

responder: Julie Crick  Replied August 21, 2024, 1:06 PM EDT
response: Hi Kathy, The leaves look like they belong to a black oak (Quercus velutina).  Before you treat the tree, please do a simple pH test on the soil around the tree. Simple pH test kits are available at any Home Depot type store or garden center. If the pH is above 7.4, then it would be time to treat the tree for chlorosis.  Happy to talk to you and your husband. I'm in the office tomorrow (Thursday) from 9:30 - 12:30, and on Friday from 8:30 - 4:30.  Thank you! -Julie