Branch Canker and Dieback Of Leyland Cypress

Disease Information

Branch Canker and Dieback

this tree is particularly susceptible to a branch canker or branch dieback. This disease may be actually caused by two fungi, Seiridium unicorn or Botryosphaeriadothidea. Seiridium canker is perhaps the most significant and damaging disease on Leyland cypress.This fungus is commonly associated with both twig cankers and twig dieback. Left unchecked, the fungus can move into the main trunk killing the entire tree. Botryosphaeria canker produces symptoms similar to Seiridium canker. This canker disease affects many woody ornamentals.

Symptoms and damage

 Both disease organisms attack plants that are stressed by environmental factors, such as wounds,drought and freezing .The mostobvious indication of the disease is thebrowning and subsequent dieback of a leader or major side branch .Sunken, dark brown cankers or patches develop on the affected branches near the transition area of healthy and diseased tissues. Small, black fruiting bodies of both fungal organisms can often be seen within these areas. Affected branch tips  turn yellow or brown.

The affected branches are usually randomly distributed on the tree. This random distribution of branch dieback is useful in disease diagnosis. Underlying woody tissue in the cankered areas is often gray or brown. Extensive resin ooze or “bleeding” on diseased branches may also occur. This symptom resembles sap flow or gummosis­type symptoms.When branches are wet from rainfall or overhead irrigation, the fungus advances rapidly, killing tissue in its wake. Entire trees may be killed if the fungi are allowed to advance into larger branches and stems.


Cultural practices are important in disease management. All infected branches should be pruned about 3 to 4 inches below the cankered area and destroyed as soon as symptoms are observed.As an added precaution, disinfect pruning blades after each cut with either 10 percent household bleach or  70 percent alcohol.Since these two canker diseases are often associated with environmental and cultural stresses, plants should be irrigated properly during lengthy drought periods. Field observations suggest that trees grown in shady conditions are more prone to develop these canker diseases. If the plants are irrigated by overhead means, this should be done during the early morning hours. By minimizing overhead water, the level of disease spread can be reduced. In nursery situations, container­grown trees should be protected from prolonged periods of subfreezing temperatures, which may create wounds on the stems. Do not take and propagate cuttings from infected plants. If Leyland cypress is to be grown as a screen, be sure to have a minimum of 12 to 15 feet between plants. Currently, fungicides are not effective for controlling this disease. Because of the widespread occurrence of this disease on Leyland cypress, homeowners may wish to consider an alternative tree for the landscape. For a list of suitable landscape trees, see FSA6126, Landscape Trees for Specific Uses, at Early detection and identification are important for effective disease management strategies. For further information about Seiridium canker and other diseases of Leyland cypress, contact your local county Extension office. 

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