Severe cupping on Tulip Poplar trees

Question: I have Tulip Poplar trees in a small stand of forest whose leaves are all experiencing severe cupping.  Only the Tulip Poplar trees are having this issue.  All other species, oak, beech and hickory, in the area look good.  I can not find any pest or disease that would be responsible for this when searching the Internet, not to this extent.  I need help.

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 June 07, 2024, 10:44 AM EDT
response: The leaf distortion resembles that caused by certain types of herbicides. While we aren't aware of research studies confirming this, anecdotally, Tulip Poplar does appear to be more sensitive to herbicide drift than some other tree species. Could any applications of weed-killer or pre-emergent herbicide have been used in the general area in recent weeks? If not, might a neighbor or farm a short distance away been making applications? Active ingredients to be suspect of might include 2,4-D and dicamba.  Drift can occur when an herbicide evaporates just enough to move on the breeze (or even just in hot weather) or when water flow during storms or heavy rain or irrigation carries residues into other areas. Herbicide exposure to trees can occur either through root absorption or as gaseous (evaporated) residues that move on the breeze into the canopy. Depending on the chemical involved and the dosage of exposure, recovery may or may not be possible. (Individual leaves that are affected or damaged cannot recover, but new growth would emerge normally if the chemical impacts wear off.)  Some plant viral infections can also cause distorted growth, but we doubt such an event would affect this wide of an area. Aphids, leafhoppers, and some other sap-sucking insects can also be common (including on Tulip Poplar) and their feeding on young leaves can similarly cause distortion and cupping. They can also transmit some plant viral diseases, though again, this is less likely in this particular scenario. Outbreaks of high aphid populations are not uncommon and could impact a group of trees in a given area, but if all foliage visible is affected, this is less likely of a cause, at least by itself. (Plenty of predatory insects and birds eat aphids, so if they are not currently visible, it doesn't necessarily mean that they were never there.)  If new leaves are not produced soon (or if they are produced, but still look deformed or stunted), see if a certified arborist can assess the trees in person. It's possible that overlapping issues are causing decline, and they can look for indications of tree stress unrelated to a potential herbicide exposure that may be contributing to the problem. (Girdling roots, for example.) Arborists cannot treat every condition, nor can they reverse tree decline (and nothing will mitigate herbicide contamination if the exposure was too great), but they can at least help make a diagnosis with an in-person evaluation.  Miri

responder: The Question Asker Replied June 07, 2024, 11:27 AM EDT
response: Hi Miri,   Thank you for your response.  I am a certified Arborist, and I am stumped by this issue.  At least 4 different Tulip Poplars in the same area are being affected by this issue and it is not localized.  The entirety of each tree has this leaf distortion.  Other trees species growing directly next to the Tulip Poplars look fine and do not have any sign of this issue.  I have inspected the area and have found no other obvious cause for the issue.  It is not a low-lying area and the ground does not appear to be saturated.  I asked the adjacent homeowner if any herbicides had been applied and they claimed that none have been applied.  All aphid populations that I find are at, what I would consider, a normal level.  I am not finding a ton of aphids.  Furthermore, Tulip Poplars down the street look normal and don't have this issue.   I am going to assume at this point that it is a virus that is affecting the trees.   Thanks.   SAMUEL

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 June 07, 2024, 11:44 AM EDT
response: Hello Samuel,  We can have our plant pathologist examine the close-up photo when he is back in the office next week, to give his impression of whether or not it's viral. While laboratory testing of leaf samples might help to reveal a cause, the exact type of virus suspected would need to be known (since the right test kit would need to be used), as well as the type of herbicide a tree might have been exposed to, in order to screen for residues (if they are even still present).  Herbicide exposure is still our strongest suspect, as a viral outbreak this extensive (or scattered across multiple properties or acres) is highly unlikely, especially having suddenly impacted entire canopies of these trees when presumably no symptoms were present last year. Perhaps the residents were unaware of an herbicide application -- we routinely field questions from Marylanders who discover plant damage from a lawn company or landscaper who applied something they were not clearly aware of or familiar with, or even which was accidentally applied to the wrong property. It's also not uncommon for such companies to contract with several properties on the same street, making a visit to them in the same day/week, and therefore we could easily see how an herbicide application made in that way would affect multiple Tulip Poplars. We have seen herbicide damage before manifesting on Tulip Poplar, Dogwood, and Redbud leaves where other trees next to them are not symptomatic.  Miri

responder: The Question Asker Replied June 07, 2024, 12:01 PM EDT
response: Hi Miri, Thank you so much.  Any help would be much appreciated.  I will follow up again with the resident about any Herbicide application.   Thanks!   SAMUEL

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 June 07, 2024, 12:05 PM EDT
response: You're welcome. We'll wait to hear from you if you glean any info. from the residents about potential applications, and will reply again once our pathologist has had a chance to look at the photos.  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 June 10, 2024, 10:46 AM EDT
response: Our pathologist looked at the photos and can't tell what the cause is, though herbicide is still suspected. (A virus is not.) Some mites that require a microscope to see can also cause leaf cupping and distortion, particularly when they feed during new leaf expansion. Time may tell whether the issue resolves itself (as a mite outbreak might) or not (if herbicide exposure was great enough). Based on the current appearance of the canopy and how sparse it looks, he thinks the tree pictured may be a lost cause, though it's hard to tell how long it might have had what looks like canopy decline, and whether its solely due to the distortion symptoms or was building up to this point over a longer period of time.  Miri