Are My Leyland Cypress Trees Healthy?

Asked May 20, 2018, 6:50 PM EDT

Hi - Thanks for providing this service. We have some Leyland Cypress tress along a part of our home's boundary line. Their height varies from about 20 feet to 30 feet. We believe they were planted about 8 to 10 years ago, although we are not sure as they were planted by our home's previous owner. The reason why I am writing is that this year, they seem have gone dry/brown but only on the inside. They are green on the outside perimeter of the trees. (Except one tree that has gone almost all dry on one side.) I have included some pictures, both close-up a from distance. Is this something to worry about? Is there something that we need to do to bring them back to health? A couple of years ago, one of our trees had a few branches that had gone completely brown. But over the summer, they grew back to full health. We are hoping it's something similar here. Also, we have a couple branches that have come out and are bending low. I think this happened when we had some snow/sleet weather events this last winter. Is that something that we need to do something about - trim them, for example? Ultimately, our real concern is the overall health of our trees. We don't know what we need to keep them in good health, if anything at all. Thank you in advance, Bhavesh.

Montgomery County Maryland disease issues abiotic issues trees pest insects and mites

1 Response

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 close together, which leads to competition for water and nutrients. As the trees mature, lack of sunlight leads to the decline of interior 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 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.

In addition, bagworms are an insect pest of Leyland cypress. If not controlled, these can also lead to browning and decline. In your third photo, it looks like there are bagworm cases. Here is more information about this insect and what you can do: https://extension.umd.edu/hgic/bagworms-trees-and-shrubs

For winter damage, there is not much you can do other than wait to see if new growth will develop (as you observed in the past) and then prune out affected areas and keep the trees well watered and mulched in times of drought. Avoid pruning when the trees are damp.

The bottom line is that Leyland cypresses look good for about 10-15 years and then they start to decline.

ckc