Disease of Leyland Cypress on the Rise

by | Jun 13, 2018

Seiridium canker causes branch dieback in Leyland cypress and is on the rise in 2018. Image: Jennifer Olson, Oklahoma State University, Bugwood.org

Leyland cypress is a popular tree in North Carolina landscapes. Desired for its fast growth and evergreen needles, it makes an ideal wind or privacy screen. However, it can’t serve that purpose very well if branches are dying. Unfortunately, that’s just what happens when seiridium canker takes hold.

This spring and summer, there are more reports than usual of seridium canker on Leyland cypress. Seiridium canker is a fungal disease that causes branches to die. When the fungus infects a branch, a canker (the name given to a dead area of the bark) forms. As the canker slowly expands, it eventually girdles the branch entirely, causing it to die from the canker to the tip of the branch. This branch dieback typically begins at the bottom of the tree and gradually moves upward through the canopy, however it could occur anywhere.

Cankers themselves can be hard to notice. Bark may be cracked or swollen, or there may be a sunken area on the stem. Often, droplets of resin are on the canker, a good indication that seiridium canker is the culprit.

Unfortunately, there is not much that can be done to control the disease. The best option is prevention; keeping trees healthy and reducing other stress agents can minimize prevalence of seiridium canker. In addition, it is recommended to prune out infected branches, cutting several inches above the canker. Between cuts, sterilize pruning shears so the fungus is not spread via equipment. Removing branches may also increase air circulation, reducing the humid conditions ideal for fungal growth. In some cases, Leyland cypress may not be the optimal selection for a site. For hardier ornamental evergreens in your area, contact your local extension agent.