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Arbor Vita Tree Turned Brown Overnight #480096

Asked August 22, 2018, 11:08 AM EDT

We are very concerned about one of our arbor vita trees that literally turned brown (more than half the tree) overnight. Please let us know your suggestions--we have taken very good care of this tree and are stumped by this damage. We don't want to lose it.

County Massachusetts

Expert Response

Hi,

Unfortunately with just a picture, it is really difficult to say what could have caused this. Arborvitae can have insect and disease problems. Evergreens rarely turn brown all at once - think about how long it takes a Christmas tree to brown after cutting it. The only think I can think of that would do something like this is herbicide drift or phytotoxicity from some other pesticide.I guess one other option might be root damage by voles. Do you see any digging at the bottom of the plant?

Your best bet would be to call the UConn Home & Garden Education Center, tomorrow or Friday<personal data hidden> and talk to one of the horticulturists on staff that day. They would ask you more questions than I can in this venue and may have some other suggestions.

An Ask Extension Expert Replied August 22, 2018, 1:02 PM EDT
Thank you for your response.  We are quite sure the damage was caused by spider mites because we found multiple webs on our trees.  We have been using water (hose spray) and neem oil to combat the problem.  The webs are fewer but do keep appearing on our evergreens, so we will keep after them.

I would like to know, given that spider mites are the likely cause) how should we deal with the tree that is left.  Should we prune back the brown sections or leave them as is?

Also, we live in Maryland (did they refer our question to you--or did I fill in a request to the wrong extension service)?  What other information sources do you suggest we pursue?  We do not want to lose this tree.
The Question Asker Replied September 05, 2018, 3:36 PM EDT
Hello,

Your question was originally sent to MDMaryland group, but for some reason then sent to UConn.
As for you arborvitae, brush off the dry needles to the ground, then check the branches to see if they are green and flexible inside or dry and brittle. If the wood is dead, the plant will not regenerate needles. Wait until spring to be sure and see if any new growth will be put out then. If not, then cut out dead branches and areas.

Neem and strong spray of hose water are adequate control measures for mites.

Regards,
Carol Quish
UConn

-Carol Quish Replied September 05, 2018, 4:47 PM EDT
Thank you very much.  When we brush the brown needles, very few come off, so we are hoping that is a good sign. We will take your advice, though, and wait until spring. We appreciate your response.
The Question Asker Replied September 05, 2018, 5:17 PM EDT

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