UGA Cooperative Extension

Jones County Extension Office:
Agriculture & Natural Resources

Release Date: May 30, 2012

By: Frank Sears, County Extension Coordinator, Jones Co.

Canker Diseases on Leyland Cypress Trees

If you are growing Leyland Cypress trees around your home and landscape you should be aware that we have primarily two different fungus diseases that can kill the branches on the trees and sometimes the entire tree. These diseases are Bot Canker and Seridium Canker.

Many people like to grow Leyland Cypress trees because of their pretty evergreen foliage and their fast growth rate. In many sites Leyland Cypress trees do well and in some other sites they seem to die right and left. Drought stress plays a major role on disease occurrence in Leyland Cypress trees so those trees that are planted on sites that have eroded hard clay soils are more prone to stress and eventually disease.

Another problem we see often in Leyland Cypress plantings is that people plant them too close together so they will serve as a screen to screen off the neighbors or the road. They grow fast and do make a good screen but as soon as they get big enough for the branches to start rubbing together from tree to tree and touching one another this also seems to provide wound openings on the branches for disease to enter the tree. Leyland Cypress trees should actually be planted 8 to 10 feet apart to allow space for the trees to grow and not grow together where they will touch and rub each other but eventually grow into a solid line for screening. If you have Leyland Cypress trees that are planted too close together – 5 to 6 feet apart – you can go in and take out every other tree to allow the adequate space for the trees to grow and not be too close together.

Finally, we have been told that even the lenticels in the bark that open and close will open up more during periods of drought stress and this allows a natural opening for disease to enter the tree. The best advice that we can give to prevent disease infection in Leyland Cypress trees is to keep them watered at least once a week during dry periods in the absence of rainfall.

The two main diseases that we see on Leyland Cypress trees are Bot Canker and Seridium Canker. Both of these diseases will usually start out killing individual branches on Leyland Cypress trees. The following information is just about a surefire way for you to tell which one of these diseases is attacking your Leyland Cypress trees.

With Bot Canker (we see this more often), you can run your fingers across the newly affected dying branches on the tree and the needles will remain attached and will not fall off easily. Bot Canker will girdle the branch quickly and so the needles remain attached to the branch after it dies. Bot Canker tends to affect one or two branches in a localized area such as at the base of the tree or where the tree branches have been pruned or injured. Bright rust colored brown branches usually occur with Bot Canker and the newly infected shoots will turn yellow and then brown. The actual canker itself can be seen on the branch and will appear sunken or cracked with a darker color than surrounding healthy tissue. Little or no resin will be seen at these canker sites.

Seridium Canker causes symptoms that more resemble drought stress. The upper branches and lateral branches tend to show signs of infection from Seridium Canker the most. The infected branches will turn yellow and then brown and eventually may become a grayish color. They don’t seem to be as reddish brown in color compared to branches killed by Bot Canker. Seridium Canker produces cankers that are longitudinal in shape and they interfere with water flow causing the branches to wilt and then die. If you run your fingers across the infected branch and the needles come off easily it will 99% of the time be Seridium Canker. Infected branches will be randomly seen throughout the tree with some being yellow, some light tan, and some brown in color. Also, resin will be seen running down the branches or tree trunk and will be coming out of the cankers where Seridium Canker infects the tree.

Always prune off and destroy infected limbs to prevent more disease infection on Leyland Cypress trees. Cut off infected branches flush with the tree trunk and paint the fresh wound with a white water based latex paint to prevent a fresh infection into the tree trunk at the pruning wound site.

Again, the best way to keep Leyland Cypress trees from becoming infected with these diseases is to purchase trees that are disease free (check limbs and trunks of young trees for cankers before buying them), space the trees 8 to 10 feet apart, and provide adequate water for your trees during drought periods.

For more information on Leyland Cypress and other trees in your landscape, call the Jones County Extension Office at 986-3958.