Browning Arborvitae Trees
Hello, I planted arborvitae trees approximately 10 years ago and they have done well until now. We traveled on vacation in Aug 2019 and when we returned home, one of the arborvitae trees was half brown. We thought it may have been the drought that Maryland experienced in Aug/September, however, after visiting the farmer's co op store, I was advised it was not diseased, but perhaps the drought. He gave me watering instructions, for once a week, however, they appeared dry and they were probably watered more frequently. The one brown tree, became two, then three and now, I think it is spreading to my Leyland Cypress (in photo). Are there any steps I can take to preserve all the trees, or should I remove the failing trees to prevent them from spreading to the others? Should I wait it out through the fall and winter to see if they rebound? Thanks for your attention to this matter.
This looks like a root issue on the arborvitae. The root system may have been subject to too much moisture, poor drainage, poor site conditions, etc. Last season and this spring we had abnormal rainfall and this can affect the root system. The saturated soil reduces oxygen and the root system declines. We also had a drought and this affects the roots as well.
All you can do is check the drainage in the area, make sure mulch is no thicker than several inches and away from the trunk of the trees. Water established plants during dry periods. The trees will have to be replaced.
Take a look at our page on planting new trees and care after planting https://extension.umd.edu/hgic/topics/planting-process
Leyland cypress - We are hearing of many problems and declines of leyland cypress, which begin to show up at the 15-20 year mark. They are not really well suited to our climate long term. Stresses such as winter injury, too much shade, planting too deeply, etc.)
can lead to disease and insect (bagworms) issues. Your tree looks like it is located in too much shade and there may be root competition for moisture and nutrients.
Here is more information, from our Maryland Grows blog recently written by our plant pathologist:
and the diseases most prevalent: https://extension.umd.edu/hgic/topics/seiridium-and-botryosphaeria-canker-leylands-trees
All you can do is prune out dead branches. Keep watered during dry periods and make sure mulch is no thicker than several inches and keep away from the base of the trunk. The tree will most likely limp along but will not return to its former glory.