Everygreen dieback

Asked September 23, 2019, 3:31 PM EDT

We have several evergreen trees (arborvite?) that are dying from the base. I don't see any obvious insect activity or other obvious problems - other than the dead branches. Any ideas, and any recommendations?

Anne Arundel County Maryland

1 Response

Evergreens have been having a tough time of it. There have been multiple and repeated stressors to them, including the tremendously wet weather last year which can compromise roots, and lately it has been droughty and dry. The spiral nature of your dieback suggests a root stress or injury.

For evergreens, winter injury or dessication is always a possible problem.
For winter damage, there is not much you can do other than wait to see if new growth will develop then prune out areas that haven't recovered. Prune only to where there is green growth. (Do not cut into the wood with no foliage. It will not regrow.) Keep the trees well watered and mulched in times of drought. Avoid pruning when the trees are damp.
We wonder if your trees are Leyland Cypress. Leyland Cypress was the 'go to' landscape plant for many years for evergreen screening in yards. In recent years it has become evident that they look great for the first 15 years or so, and then start to decline. Very often we see them planted too closely together, which leads to competition for water and nutrients. As the trees mature, lack of sunlight to the interior of the tree leads to the decline of the inner branches.

Stressful conditions like drought or cold winters can make Leyland cypresses susceptible to different insect pests and diseases. Common problems include 'winter burn', which is a browning desiccation injury from drying winter winds. We have seen a lot of this type of injury in Leylands this year. Here is an article from our plant pathologist about this: https://marylandgrows.umd.edu/2018/04/11/why-is-leyland-cypress-turning-brown-winter-took-its-toll/

Much more serious are canker diseases and needle blight. Here is a page about these diseases and the symptoms to look for: http://extension.umd.edu/hgic/plants/seiridium-and-botryosphaeria-canker-leylands-trees No fungicides are effective for these diseases.