Leyland cypresses with fungus?
Dear experts, I have 10 cypresses forming a fence. They are around 10 years old. They show signs of stress, such as dead branches and dark areas (see photos). I would say that 80% of the branches look fine, but 20% are dead, mostly in areas with less light. I wonder if this is a fungus and what should I do to improve the health of the trees. Thank you very much in advance for your help!
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. New growth this spring may flush out and the old needles will drop out. You can always prune out any brittle, dead wood that you see. (The trees cannot grow green tips or branches back from the trunk area.)
There are multiple reasons for problems, but just like for us humans, stressful conditions like drought or cold winters can make them 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 a recent 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.
There is not much you can do other than to prune out affected areas and keep the trees well watered and mulched in times of drought. Avoid pruning when the trees are damp.