Sick Japanese Maple Tree

Question: We just noticed parts of our Japanese Maple is dying.  Other parts leaves seems a little unhealthy on close examination, but look fine from a distance.  
We are not sure when this issue started. We hope this is treatable and request your expert opinion and advice so we can hopefully save this tree.  Thank you very much for your assistance.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 28, 2024, 11:59 AM EDT
response: Hi,  Have you watered the tree last summer and through the heat of this summer? The leaf symptoms on the leaves that are still alive look scorched from either sun, heat or drought stress and given our extreme heat days this summer that makes sense.  Japanese maples can be susceptible to a canker disease called Botryosphaeria. It is a fungal disease that can affect woody plants especially when they are stressed from insufficient watering. (The link provided shows rhododendron shrubs but Japanese maples have similar die back).  Many plants can still live a long time with the fungal disease. Just prune out the dead branches. You will want to examine the inner part of the branch and cut 6 inches below any darkened wood. Here is a link from a Virginia Tech article on Botryosphaeria in trees and shrubs and it has some photos of what to look for.  Alternatively it could be root die back from a variety of causes. Again drought stress could be a main factor. You can examine around the base of the tree and into the liriope and pachysandra ground cover to see if there are any burrowing holes or chewing you may notice at the base or on roots slightly under the ground level. It could be vole damage.  Is the root flare exposed at the base where the trunk meets the soil? It should look like the stem of a wine glass coming straight down then flaring out at the bottom. If it is buried in mulch or planted too deeply it could have grown a girdling root that is now cutting off the flow of nutrients in the trunk to the upper branches, causing die back. This can be sometimes fixed but if there is a girdling root, sometimes it is too late to correct with out harming the over all tree. You could dig out some soil and mulch and around the roots to see if you notice one. The link shows a photo of girdling roots and explains how this can harm a tree. If you can prune out the dead branches and mitigate stress for the tree by watering in times of drought and making sure it isn't buried too deeply, it should hopefully be ok for years to come.  If you notice further symptoms, feel free to send in additional photos.  Emily

responder: The Question Asker Replied September 09, 2024, 3:24 PM EDT
response: Hi Emily, Thank you VERY MUCH for the very informative and detailed response. We have watered throughout Summer via our irrigation system, but it may not have been adequate possibly due to presence of the ground cover directly under it possibly preventing enough water to get to the root system. We moved to this house in January and are unfortunately new to gardening.  When I was trying to see where we may need to cut the dead branches off, I noticed an area on the trunk which is upstream of all the dead smaller branches.  I am including a few photos showing the dark discoloration and bark peeling off in that area.   Is this what Botryosphaeria is expected to look like or could this be another disease?    With respect to this area with no bark, where should we cut the branch?  Should we start the first cut right below where the bark is peeling, then continue cutting small sections and inspecting the interior of the cut surface to see where the internal discoloration ends (assuming this is Botyrosphaeria) and then make the final cut at 6 inches below the section which didn't have discoloration in the cross-section?Thanks again for your expert advice!

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied September 10, 2024, 12:26 PM EDT
response: Our pathologist saw the photos and confirmed it looks like Hypoxylon canker which can effect hardwood species such as maples and oaks, hickory etc. (Oklahoma State web resource) You can prune this out and keep moving back with pruning cuts until you reach inner wood that looks healthy and clear (so white or greenish on the interior and no black legions). To keep it from spreading it is recommended that you prune back 18-24 inches into the healthy branch. If you can't do that because of how they bend to the trunk just go back as far as you can into healthy wood.  You can refer to our page on proper tree pruning to help, and I have included a photo of examples where you can try cutting, starting at 1 and working to 3 if needed. The yellow circle could be early stages of it as well before it ages to black but it is difficult to see in the photo angle and lighting to know for sure. Let us know if you have further questions.  Emily

responder: The Question Asker Replied September 11, 2024, 5:25 PM EDT
response: Hi Emily, Thank so much for the additional information and great resources. The pruning reference is very informative. It seems like the new diagnosis is even worse than we thought. It is devastating to see the demise of this beautiful tree. We cut at #1 location (per your annotation) and I think I see some minor discoloration on the cross-section, but it is a lot better than what we saw on the cut made where the bark was missing and the dark patch was visible. Cutting further down at #2 will remove a very large area of the canopy ( more than half at least). Should we perhaps hold off and do more cutting only when/if additional sections of the canopy also dies? Is there a possibility if we provide better condition the infection could possibly be contained?  I put a container under it last night and after this morning's irrigation, there was less than one quarter inch water in it, if even that. So it seems like the irrigation wasn't doing much for this tree. I wish we had realized this a lot sooner. Going forward we will water it manually. Should we do a soil test to see if it needs amendment/fertilization?  When we made the cut, the cross section on the branch that came off immediately developed a very dark/black section (like ink seeping inside) from under the bark in 2 distinct areas. This didn't occur on the cross-section attached to the tree. What is this? Is it a different organism than the hypoxylon? I am including a photo of both cross-sections. I don't know what normal bark for this type of Japanese Maple looks like. I have included 3 images in the PDF. Some places there is a silvery bark towards the upper part of the branch (facing the sun or outwards?), and the lower part is green. There are other patches that look like mosaic-not sure that is the best description. These look very different from each other. Hopefully this is how normal bark looks like? Thank you for reviewing the images and commenting. Thanks so much for all your expert advice.  Morvarid

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied September 12, 2024, 11:56 AM EDT
response: Hello Morvarid,  You can wait to prune more if the current branch removal showed no substantial inner wood discoloration, which appears to be the case in your photo. Various canker infections can cause very similar-looking outward symptoms, and sometimes it's hard to determine exactly which was the culprit. In some ways, that doesn't matter too much, since there is no fungicide remedy for them and pruning out the damage is all that can be done once they manifest.  We often see irrigations systems programmed incorrectly (in terms of how their use would best benefit plants). A common occurrence is systems programmed to run too often and too briefly; watering should be infrequent enough to allow the soil surface layers to dry a bit between waterings (to avoid over-watering), and the system run long enough that about an inch of "rain" is provided. You test was a good one, and perhaps the system is only running, say, fifteen minutes every couple of days or so. In either case, manual watering can be a good way to spot-water plants that need it and avoid plants that don't, which an irrigation zone would otherwise water uniformly (for better or worse based on soil drainage differences or plant needs).  When watering manually, soak the root zone well but only when needed, which can be determined by feeling the soil about six inches deep and watering only once the soil becomes somewhat dry to the touch at that depth. (If damp at that depth when checked, watering is probably not needed.) Maples appreciate more even soil moisture levels, but like many plants, do not want to stay damp/wet for long periods. If a roof downspout outlet happens to empty near the plant's root zone, that's something to take into consideration, since in rainy periods, that will put extra water into the root zone. (This summer, that wasn't as much of an issue for most areas, since it was so dry.)  A laboratory soil test is always informative, though might not be needed for this situation. Still, it will assess nutrient content, acidity level (pH), and organic matter level. Fertilization of established plants is usually not needed, and plants suffering from a pest or disease issue (or environmental stress) generally are best not fertilized, since the added nutrients (which might not be deficient in the soil) could further stress the roots. If mild fertilization will help to encourage regrowth after the loss of some branches/foliage, then wait until spring to apply it. We can help to interpret soil test results if desired. Soil nutrient deficiencies drastic enough to cause poor tree or shrub growth aren't very common, though sometimes pH could use some tweaking. We do not see indications that pH is affecting the maple, since different leaf symptoms (that we don't see) would be present. Lab soil testing won't be able to diagnose a dieback issue due to infection, but if you want to have one done, there is certainly no harm in it.  We can't quite tell what caused the inky black residue, but it looks to small and contained to be a symptom of infection, especially since it wasn't on both sides of the cut. (Could it have been residue from the saw itself?)  Bark characteristics can vary with wood age and tree species/variety. In this case, none of the pictured areas look immediately concerning, so you can just monitor the tree for changes. Early stages of Hypoxylon infection can look silvery and smooth, but not quite like the images you shared, a bark feature which we've seen often with what appear to be healthy Japanese maples. Bark often does go from greenish and smooth to more gray/brown and textured as branches and trunks age and increase in girth, so over time you will see some changes in its appearance, which are usually normal. Moss and lichen could also grow on the bark at some point in the future, which is fine if they do, since they don't cause damage to the tree.  Miri