Arborvitae problems

Asked August 28, 2019, 12:17 AM EDT

We have a row of very well established arborvitae that have been looking good for many years. One died last summer and then earlier this summer another died, and a third just went from green to brown within a week. I had someone look at them and found they were infested with some kind of bug that probably bore into the branches and left two more plants with hollow sounding trunks. They may be spider mites, but I'm not sure. There are lots of white spots on many of the branches. I'm not sure if the white spots are related to the bugs on the inside or not. There are spots and clumps of white stuff on most of the rest of the arborvitae. I'm afraid the rest of them will die and I REALLY don't want that to happen. I read that a good start to address this problem is to blast the trunk and branches with a sharp spray of water. I tried that tonight, but the spots and clumps are still there.

In a different, but possibly related issue, another plant across the yard started dying. The trunk and branches turned black. Upon further inspection, I found white spots that look like the ones on the arborvitae.

I'm including pics of the arborvitae and then the other plant with blackened branches. If anyone knows what's going on with these plants, we'd really appreciate any info.

Thanks in advance!

Clackamas County Oregon arborvitae

1 Response

Thank you for your question. First, the white spots appear to be lichens, which don’t cause any damage, but are often found on woody plants that have problems. Second, we need to see a photo of the entire plant to spot trends in the problem(s). Third, we cannot diagnose the trunk and branch blackening on a plant without knowing the plant species and seeing the entire plant. I suggest you take these photos, more as described above, and plant samples into one of the 3 metro Extension offices for help. Here are the 3 possible sites: https://extension.oregonstate.edu/mg/metro/have-gardening-question Good luck!