I have an Arborvitae that has been planted in a berm for about 3 years now and it is quickly turning orange and appears to be dying. I haven’t seen any little black fungal spors or visible bugs on the tree. I have also noticed some small similar looking orange branches on some of the other arborvitae in the same hedgerow. What could be killing them and is there anything I can do to stop/reverse the damage?
Jackson County Oregon
American Arborvitae (Thuja occidentalis) species grow best in well -drained soils ( you have planted on a berm, we assume, to improve the drainage), but unfortunately that excellent drainage can also produce drought, very quickly. The currrent low rain season probably has much to do with weakening the plants. They need moist air and lots of soil moisture to look their best. Drought can also invite unwanted pests, such as spider mite. These tiny, usually reddish insects can sometimes be detected by taking a sheet of white paper, holding it under an affected branch and shaking the branch over the paper. Then check to see if there are any crawling insects on the paper. Spider mites can be dislodged in the nymph (newly hatched) state by strong sprays of water. Consult the PNW Handbook on Insects (pnwhandbooks.org/insects) for further information on spider mite treatment, if necessary..