Yellowing Arborvitae

Question: Hi! We have a very old arborvitae hedge (70 years old?) that has one spot that is yellowing. It happened over the course of just a few days, but so far it seems to only be one small section.

Last year we removed a great deal of grapevine that had begun to threaten the health of this hedge, but other than that, no change has been made to our yard care or hedge care. We have not experienced this in our 7 years with this property. Any advice? We’d be heartbroken to lose this amazing privacy shield!


In appreciation,
Tasha

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied September 20, 2024, 6:05 AM EDT
response: Hello Tasha, Thank you for submitting your question to the UVM Extension Master Gardener Helpline. You have a beautiful hedge there. It is interesting that it only seems to be this one area so far, though there is some loss from the middle of other trees.  There are several possibilities. Seasonal needle drop is normal where older, inner foliage turns golden brown to rust brown, without any spots. Foliage drops, usually in September or October. I assume you have not seen it to this extent before so let's consider other possibilities. Is there grapevine left on this tree? Was more pulled off this particular tree? Is that tree in a depression where it is particularly wet or is it too dry? Dig a hole near the base of the tree and put your finger down about 4 inches to try to determine if it is muddy or too dry. Browning of leaves can be caused by either Arborvitae diseases should also be considered. Please look at the affected areas for fine silk between needles (spider mites) or black, brown or gray powdery patches or coating on foliage and twigs (sooty mold). I am including a link to a U Minnesota Extension site that walks you through a variety of symptoms to look for in pull-down menu format to help diagnose and treat your problem.  https://apps.extension.umn.edu/garden/diagnose/plant/evergreen/arborvitae/index.html I will also pull in a collaborator who may have other thoughts.  Thank you for including a photo. A close-up photo of one of the affected areas could be helpful as well.

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied September 20, 2024, 12:22 PM EDT
response: Hello Tasha, Thank you for submitting your question to the UVM Extension Master Gardener Helpline. You have a beautiful hedge there. It is interesting that it only seems to be this one area so far, though there is some loss from the middle of other trees.  There are several possibilities. Seasonal needle drop is normal where older, inner foliage turns golden brown to rust brown, without any spots. Foliage drops, usually in September or October. I assume you have not seen it to this extent before so let's consider other possibilities. Is there grapevine left on this tree? Was more pulled off this particular tree? Is that tree in a depression where it is particularly wet or is it too dry? Dig a hole near the base of the tree and put your finger down about 4 inches to try to determine if it is muddy or too dry. Browning of leaves can be caused by either Arborvitae diseases should also be considered. Please look at the affected areas for fine silk between needles (spider mites) or black, brown or gray powdery patches or coating on foliage and twigs (sooty mold). I am including a link to a U Minnesota Extension site that walks you through a variety of symptoms to look for in pull-down menu format to help diagnose and treat your problem.  https://apps.extension.umn.edu/garden/diagnose/plant/evergreen/arborvitae/index.html I will also pull in a collaborator who may have other thoughts.  Thank you for including a photo. A close-up photo of one of the affected areas could be helpful as well. Dr. Hazelrigg weighed in to say that fungal diseases may be involved due to the wet weather we've had this and the past few years. Heavy clay soils would also retain more water. She suggests pruning out dead parts late fall or winter and the tree may recover.

responder: The Question Asker Replied September 20, 2024, 2:10 PM EDT
response: Thank you for your thoughts! Everything is dry right now, but as these trees are so old, I’m surprised they’re being so affected. We’ve never watered them in the past, and we’ve never seen this much yellow happen!There was quite a bit of grape within the hedge, but it was removed last fall and we were starting to see the trees thinking about filling in the thin spaces left by the vines.None of the pictures on the great website you directed me to match this problem. It seemed to come on very suddenly and progress quickly.On Sep 20, 2024, at 12:22 PM, Ask Extension wrote:﻿

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied September 22, 2024, 4:57 AM EDT
response: Hi Tasha, Thank you for the close-up photos. I am not seeing mold or spider mite either. This may be normal fall leaf drop, and affecting this tree earlier of more severely for one or several of a variety of reasons (planted at different depth, more prior grapevine). See this reference on normal fall leaf drop https://ag.purdue.edu/department/btny/ppdl/potw-dept-folder/2022/normal-needle-drop.html If the branches are still flexible and not dry and brittle, they are likely OK. This part of the reference may be particularly helpful to you. "How can you tell if the branch will survive? "First check to see if the branch with the browning needles is alive. Scrape off a small area of the "bark" of the branch with a sharp knife. There should be green tissue immediately under the bark. This green cambium layer is quite thin with the underlying woody tissue being white. If there is no green at all, the branch is dead. Also check the ends of branches. Dry, brittle twigs indicate that at least that part of the tree is dead. Dead branches should be removed".  I also wanted to mention that given the age of this hedge there could be some loss as the trees reach the end of their lifespan, though some arborvitae live to be 100 or so. The foliage does tend to thin as they age. https://extension.psu.edu/the-mighty-arborvitae Good luck with this and I hope the information is helpful.