16 yr.old locust tree, leaves are Yellow/Brown and falling off the tree

Question: Leaves were first healthy, looking and bright green. Then in the past 3 weeks, sections of tree the leaves turned yellow brown, and  have fallen off.
And this condition has spread to other parts of the tree.
I don’t see any signs of insects or sap running from tree.
Any help would be appreciated
Thank you

responder: An Ask Extension Expert Replied July 12, 2024, 10:43 AM EDT
response: I'm sorry to hear about your tree! From the photos it's tough to narrow down the cause--a few different things could cause symptoms like this.  Can you tell me, please, in what conditions the tree is growing (a lawn, mulch, etc), how it is watered, and what is on the other side of the fence? Cordially, John

responder: The Question Asker Replied July 12, 2024, 1:13 PM EDT
response: Good morningThe tree (trunk is about 12inch diameter) is planted in rock and about 5 feet away goes into the lawn. On the other side of the fence is rock and then goes into neighbors lawn. This morning, I noticed some yellow leaves, this usually happens in the fall before the leaves fall off. I normally do not have to water the tree, in the past it seems to be growing just fine. This is the first year I ever had any issues. Again, any helpful suggestions would be appreciated. If you Need any further, information please let me know. Thank you,  Sent from my iPad On Jul 12, 2024, at 8:43 AM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: An Ask Extension Expert Replied July 12, 2024, 3:17 PM EDT
response: Thank you. This could be caused by root damage or possibly by the honeylocust spider mite (or perhaps also the honeylocust right mite).  During heavy mite infestations, large portions of the crown may turn off-yellow and the leaves will drop prematurely.  Mites are usually problematic for trees in dry sites; if the tree is getting water from turfgrass they are less likely to be the culprit.  If you are able to look closely at the yellowing leaves you can check for the presence of the mites, which are light green/yellowish, and quite small.   Root damage may have been caused by under- or over-watering, though if this is the first year for damage and your watering practices have not changed, this seems unlikely as well. Another possible cause for root damage or leaf-drop like what you're seeing is damage from herbicides.  Do you know if any herbicides have been used in the rock areas on either side of the fence? John

responder: The Question Asker Replied July 12, 2024, 3:34 PM EDT
response: I have not used a herbicide But I cannot say if my neighbor has on his side of the fence or not. Since we’ve had some hot and dry weather, Would it be a good idea to feed and deep water the tree around the drip line with a deep water needle attached to a water hose? Thanks again for your help    On Fri, Jul 12, 2024 at 1:17 PM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied July 15, 2024, 11:39 AM EDT
response: Hi Nick, Watering is almost always helpful in Colorado--though you don't need to bother with a "deep-root" wand or anything--just set a low hose or low sprinkler to water the tree's rooting area, which includes several feet beyond the dripline.   Fertilizer may make things worse--a stressed tree will at best not be able to use the resources; at worst it will respond by trying to push a lot of growth, ultimately deepening its stress.  If the tree recovers, you could consider a very light fertilizer application next spring. Were you able to check for mites or other possible causes of root damage? Cordially, John

responder: The Question Asker Replied July 15, 2024, 2:50 PM EDT
response: Hi againI accidentally sent the first response to you Here are some pictures of the base of the locust tree  about a foot to a foot and a half from the tree trunk seems to be slightly raised Does this mean that the base of the trunk is bulging? And cause a problem? By the way, I did water  Thanks again for your help Sent from my iPhone On Jul 15, 2024, at 9:39 AM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: The Question Asker Replied July 15, 2024, 2:50 PM EDT
response: Thank you for getting back to meDid check for mites, and there doesn’t seem to be any visible issues.  Sent from my iPhone On Jul 15, 2024, at 9:39 AM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: An Ask Extension Expert Replied July 15, 2024, 3:23 PM EDT
response: Hi Nick, The ground swelling is likely not a sign of problems, though I do notice that you have weed fabric surrounding the tree, which can restrict water and airflow to the root zone.  Consider removing it from beneath the rocks from the area around the tree.   Another thing to examine closely is where the trunk of the tree enters the ground--the side toward the photograph looks like it has good trunk flare, that is, the trunk begins to spread out just before transitioning to roots at the soil line.  On the side nearer the shrub, though, it looks like the trunk may enter the ground straight (like a telephone pole), which could indicate either a rot, or possibly a girdling root that could be damaging the canopy as well.  If you find that the trunk flare does not go all around the tree, gently excavate until you find the flare, and look for girdling roots or signs of decay. More information about girdling roots can be found on page 4 of this document: https://cmg.extension.colostate.edu/Gardennotes/659.pdf Cordially, John