Diagnosing and Managing Branch Canker in Leyland Cypress

Evergreen Tree

Identifying the Problem

A homeowner noticed their 10-year-old evergreen showing significant dieback, with branches turning yellow then brown, predominantly on the west side. Despite regular watering and a previous bagworm treatment, the tree declined. Sap seepage from the trunk raised concerns about insect activity, though no obvious infestation was found.

Expert Diagnosis: Branch Canker

The tree was identified as a Leyland Cypress, a species highly susceptible to Branch Canker (caused by Seiridium or Botryosphaeria fungi). This disease causes flagging, browning, and death of individual branches, often starting on one side of the tree. The provided University of Arkansas extension publication (FSA-7536) offers detailed identification and management guidance.

Contributing Factors and Immediate Actions

• Water Stress: Drought stress predisposes trees to canker. Maintain consistent soil moisture—deep, infrequent watering is best.
• Mechanical Injury: Check the base for string-trimmer or mower damage. Bark wounds create entry points for pathogens.
• Pruning: Remove dead branches during dry weather, cutting 6–8 inches into healthy wood. Sanitize tools between cuts.

Follow-Up: Bark Loss at the Base

The homeowner later reported bark sloughing off at the base (not from equipment). The expert clarified that Branch Canker typically affects upper branches, not the trunk base. Possible causes include animal chewing (though no tooth marks were seen) or abiotic cracking. Since the wound interrupts vascular flow, recovery is uncertain. Recommendations:

• Encourage vigorous growth with proper watering and mulching (≤3 inches deep, pulled back from trunk).
• Avoid wound dressings—they can trap moisture and hinder natural compartmentalization.
• Consider installing hardware cloth around the base to deter animals.
• If the tree declines further, replacement with a more resistant species may be necessary.

Long-Term Outlook for Leyland Cypress

Leyland Cypress grows rapidly (40–50 ft) but is prone to canker, especially in dense screen plantings. Diversifying with multiple species reduces disease risk. Regular monitoring, prompt removal of infected material, and minimizing stress are key to prolonging tree health.