Sick Leyland Cypress tree
I have several Leyland Cypress trees. Two of them look very sick. I'm not sure what is wrong. One is worse than the other. Is there anything I can do to save these two trees? I planted them about five years ago. 15 went in - 8 on one side of the property, 7 on the other side. Both of these trees are on the east side of the house with a southern exposure.
There are likely multiple things going on. 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, poor drainage (the root systems will be affected in soils that drain poorly or standing water), 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. Here is an article from our plant pathologist that addresses some of the common problems with Leylands: https://marylandgrows.umd.edu/2018/04/11/why-is-leyland-cypress-turning-brown-winter-took-its-toll/
In addition, bagworms are an insect pest of Leyland cypress. If not controlled, these can also lead to browning and decline. https://extension.umd.edu/hgic/bagworms-trees-and-shrubs
There is not much you can do other than prune out dead branches and wait to see if new growth will develop. (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. Also, see if you can improve the drainage in the area.
The best plan is to diversify the planting in the area when a tree declines. A mixed planting will be more forgiving if you start losing them to poor site conditions, insect , or disease issues. Plan for mature height and width based on the site.