What's causing the brown edges to leaves of our Tulip Poplar

Question: Our @ ten-year-old tulip poplar has newly developed brown edges to virtually every leaf. What is the likely cause? What should I do about it? How serious or fatal could this be for the tree?  We're in Talbot County -- the tree has been getting plenty of rain in the last month - since June's drought. Once or twice a week in light and/or sometimes heavy doses. It's been very humid too. Thanks in advance for your help on this!

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 July 17, 2023, 4:36 PM EDT
response: We can consult with our plant pathologist as soon as he's back from an out-of-state conference, but these symptoms appear to be abiotic. (That is, not due to a living cause like a pest or disease, but rather environmental conditions or physical damage.) In the meantime, several questions will help us narrow-down a possible cause:Has anything changed in the plant's environment since just before these symptoms began?Is its trunk base uninjured, such as from mowers or weed-whackers if it is surrounded by lawn?Is anything tied to the trunk that is getting tight or causing an abrasion or wound, like ties to a stake or an old plant tag from the nursery? (A tag wouldn't likely last that long to not have degraded in weather and fallen off, but it doesn't hurt to ask.)Was anything applied to the ground/soil near the tree recently, like fertilizer or a pesticide?Is it receiving more or less water than it used to, such as from a redirected roof downspout outlet or changed drainage patterns in the yard?Was any digging done near its root zone in the past year? For example, utility work or re-grading done to address a moisture problem near the house or other parts of the yard. Can you share a photo of the tree overall so we can see how it's growing and if there are any other concerning symptoms?  Miri

responder: The Question Asker Replied July 17, 2023, 4:59 PM EDT
response: Miri – Thanks for your super-prompt response. Answers to all the questions – NO. Although there does look like some superficial scarring on one side of the trunk from lawn guys’ weedwhackers. It’s not even ¼ inch deep, though.     The tree may not be happy about the weather  - but everything else is as it has been since we planted it.     Please let me know if you prefer I resend this back through the website – or whether the photo gets blocked by your email?    Look forward to hearing more. I’m worried about our tree (grown from a seed from a tulip poplar at Mount Vernon – planted by George Washington! I used to work at American Forests, which had a Historic Tree program at the time).    Thank you again,    Lea

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 July 18, 2023, 9:56 AM EDT
response: We received the photo, thank you. (We can't enlarge it but it should suffice.) A close-up of the scar you mention might be useful.  Is there any mulch around its base? We don't see any, but it's hard to tell. If not, it will be at greater risk for trunk injury and the roots are competing with the turfgrass, so ideally it should have a ring of mulch around the trunk base, perhaps about 2 to 3 feet out in all directions given the tree's current size and no thicker than about 3 inches deep. (Keep mulch from touching the trunk itself.)  Miri

responder: The Question Asker Replied July 18, 2023, 10:24 AM EDT
response: Miri – Many thanks for the info – though I don’t think that’s necessarily the answer. I just checked and yes, about a third to half the circumference of the trunk has been girdled about ¼-1/2” deep by lawn service weed-whackers. I have put a chicken-wire plant cage around it (4” – 6” wider than the trunk itself, to keep them from getting close. Will add mulch around that – if desirable?     I’m sending pix of the entire tree and of the girdling – for further scrutiny. They’re larger size so I hope they go through ---  THANK YOU for your attention to this!    Lea

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 July 18, 2023, 3:01 PM EDT
response: Thank you for the other photos. That is a concerning amount of girdling or bark damage, but it might not have cut into the sapwood yet (hard to tell); sapwood is vital tissue that lies just underneath bark and it cannot be treated if injured or infected. Yes, mulch is still advisable even if a protective cage is used because not only does it act as a buffer from lawn equipment and any herbicide applications made there, but it also replaces the turf closest to the tree which should reduce how much competition it faces for moisture and nutrients. If deer visit the yard, the cage shielding the trunk will also reduce the risk of "buck rub" (autumn antler rubbing on young tree trunks that bucks do to remove velvet), which can be similarly very damaging or fatal for a young tree.  For the time being, continue to monitor the tree's watering needs by feeling the soil about six inches deep and watering well if it becomes somewhat dry to the touch at that depth. Our rainfall hasn't yet caught up with the year-to-date drought and not all rainstorms are soaking in well enough to rehydrate stressed plants. (To be fair, Talbot County is not as badly affected by our rainfall shortage as most of the state.) We'll be in touch again once we have feedback from our plant pathologist, even though a disease being responsible for these symptoms is unlikely.  Miri

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 July 19, 2023, 12:10 PM EDT
response: Hi Lea,  Our plant pathologist agrees the scorched leaf margins point to root stress (possibly root damage) but in lieu of any digging or drastic moisture changes around the roots then the trunk damage is definitely suspect as at least a partial contributing factor. We can't tell if the pictured damage is serious enough below the bark to be a sole cause of the canopy stress, but it should be prevented from worsening by the protective measures you're now taking. No treatment can be applied that will remedy the situation for now, but if nothing worsens, the tree will probably recover sufficiently well on its own. New foliage growth to replace the damaged leaves (which can't heal) is unlikely this late in the growing season on trees but next year's leaves should emerge normally. Fortunately, enough of the leaf surface on those burnt leaves is still functional and able to photosynthesize to feed the plant, so despite being an eyesore they at least are still beneficial for the tree to keep.  Miri

responder: The Question Asker Replied July 19, 2023, 1:24 PM EDT
response: Thank you, Miri! On Jul 19, 2023, at 12:10 PM, Ask Extension <<personal data hidden>> wrote:﻿

responder: Answered by theHome 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 July 21, 2023, 9:21 AM EDT
response: You're welcome.