Arborvitae browning branches

Asked June 14, 2018, 5:58 PM EDT

Hello, My husband and I moved from south Corvallis to Lewisburg area and our new home came with 30 arborvitae. They seem to have been here for about 10-15 years and all are in excellent health. Or, they were. Suddenly, after two years of living here, I can see branches dying. A branch here, a branch there, several on one tree. A few other brown patches scattered among 6-8 of the trees. This is happening fairly quickly, too. We don't water them. They've seemed to have been fine with little care...just an occasional pruning. They aren't being over-watered or under-watered. I can't tell what the cause might be. It doesn't seem to be a spider mite or caterpillar damage. These are a very important part of the landscape and we're really scared that we could lose a hugely valuable and needed THIRTY trees. They provide privacy for us and habitat for wildlife, plus their aesthetic value. Any advice is more than appreciated. I'll include images (one of a dead section, one of some sections dying and one possibly beginning the dying process). I did cut out one large branch, but couldn't diagnose anything. It just looked.....dead. :( Thank you very much. [New info....6/15/2018...I finally got the largest dead branch sawed out and I *think* I found a couple of tiny holes. So, possibly 'bark beetles'? My research says bark beetles mean we most likely will lose some, or many, trees and there's few to no treatments. These are very healthy trees! Not sure what to do now. Insecticides don't work, they spread before you know they're there. By the time you see brown death, the tree's a gonner. This is awful. Is there *anything* to be done?]

Benton County Oregon

2 Responses

I'm so sorry to hear that you are losing trees! Know that you are not alone, we have been receiving reports of stressed woody plants from all over the valley.

I know you're not a small woodland owner, but I'll refer you to the OSU Extension blog called TreeTopics for a long version of what's going on. The short version is that our summers have been extremely hot and we've been under drought conditions for several seasons.

Even an established tree or shrub may have needed irrigation to thrive. It takes a while for woody plants to show the stress unlike the herbaceous plants in the landscape. If you can provide irrigation (drip line, micro emitter, etc.) that may be beneficial as we are following a very dry May.

You mentioned possibly seeing insect damage from bark beetles. Many insects are attracted to stressed trees, so the insects may be a symptom of a problem but not the primary cause of the tree stress/death.

Good luck and thanks for reaching out to Ask An Expert!

Many...MANY thanks for your response Brooke. We are so grateful and are now working on a drip irrigation for our arborvitae. Cheers!