Damage to peak branches on healthy arbor vitae

Question: Hello, we live in Rockville. We have had arbor vitae in our backyard for over ten years. I spray them several times of year with deer repellant and we have been spared the deer eating the lower limbs. We were surprised this weekend to find a hole in the top of one of the trees as if something had ripped out some of the branches. The rest of the tree is healthy as are the other trees.
Do you have any thoughts as to what might have caused this damage?
Anything we need to do to enhance growth to repair the defect?
Thanks,

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, 1:43 PM EDT
response: This is surprising damage being so high and localized and we're not quite sure what caused it. Too high to be deer browsing, maybe other wildlife chewed branch tips instead. Squirrels, for example, gnaw on lots of tree twigs either for gathering nest-embellishing materials or to simply wear-down their ever-growing teeth, though we don't recall seeing examples of squirrels climbing into Arborvitae in this manner since they have fairly thin and dense branches except for the main trunk. (To be fair, gray squirrels are day-active and more noticeable but flying squirrels are reclusive and nocturnal and also found state-wide.)  Bagworms would be visible as they matured and their bags got bigger, and would tend to cause a bit of browning as the foliage they ate into dried out. We don't see obvious bagworms in the photo, but can't rule them out as they are not yet full size at this point in the summer. If you have binoculars you can periodically inspect this part of the plant with, that might help reveal the presence of any bagworms if they are the culprit.  Nothing can be done to repair the defect, but in time, as long as the gap doesn't worsen, the surrounding growth can gradually fill in and cover that area up. There is no need to fertilize and you can just continue to periodically monitor the plants for watering needs given our region-wide shortage of rainfall to date this year.  Miri

responder: The Question Asker Replied July 17, 2023, 6:19 PM EDT
response: Miri:Thank you for getting back to us so promptly. We remain baffled.    We will monitor the other trees in the interim.   We very much appreciate having this resource available to us at the Univ of Maryland.   Best regards, Anthony and Kathleen

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, 9:40 AM EDT
response: You're welcome!

responder: The Question Asker Replied July 31, 2023, 6:56 PM EDT
response: Good evening: We thought it would be useful to provide you with a followup regarding the branch removal on our arborvitae. The defect appears to be getting larger. I had sprayed the area with insecticide for bagworms (although none were seen), a fungicide, and a deer repellant that repels small animals as well (e.g.  squirrels, raccoons). While my wife was sitting in our kitchen this weekend, she noted a squirrel climb up to the area that is denuded and rip small branches away dropping some and running away with some, possibly for a nest. Why this particular tree? We suspect there was a birds nest in that tree as we found small robin eggs in our garden that were split in half, possibly from a nest invasion. This is very annoying. I have sprayed the animal repellant again in that area and I will trying to place some netting over the defect to see if it can recover. Hopefully the squirrel will not be incentivized to look at another one of our trees. Thank you, Anthony

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 01, 2023, 3:48 PM EDT
response: Hello Anthony,  Thank you for the follow-up. It's interesting that a squirrel was indeed the presumed culprit, based on what she witnessed. Perhaps it finds something in that foliage appealing for nest construction (maybe leaf chemicals that help repel pests like lice or something...birds sometimes do the same with certain leaves). Unfortunately, squirrels are very hard to deter or exclude from any plant, so we don't have a suggestion beyond repellent spray use and maybe trying some reflective material to scare it away, like Mylar strips that blow in the breeze. Your attempt at using netting is certainly fine try also since generally a physical barrier stands the best chance of excluding it, though hopefully the squirrel (or a bird) won't get caught in it since some types of netting catches on just about anything fairly easily and can be hard for animals to detect until they run into it. (We acknowledge that either Mylar strips or netting may be impractical to try to get up into the tree, though.) A squirrel could very well have preyed-upon a bird nest, but as to why it seems to be favoring that one tree above the others, we don't know.  Miri