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Diseases of Leyland Cypress

Publication Number: IS1658
View as PDF: IS1658.pdf

Leyland cypress (Cupressocyparis x leylandii) is a feathery-leaved evergreen that has rapidly gained popularity in Mississippi. A reputation for rapid growth and hardiness have made Leyland cypress a popular choice for Christmas trees, privacy hedges, and windbreaks. These uses, coupled with the climate and site conditions common in Mississippi, can reduce the vigor of Leylands and make them more susceptible to certain diseases.

Diseased Leylands in Mississippi often are seen growing on low-lying sites or sites that have heavy clay soils and poor drainage. Leylands require well-drained soil and do not appear to tolerate “wet feet.” Poorly drained soils increase plant stress and susceptibility to disease. Trees on sites with poor drainage often have severe twig dieback problems, whether they are open-grown or in hedges.

When planting Leylands, check that the root ball is not pot-bound. Roots that are pot-bound have hit the inside wall of the pot and, unable to continue growing outward, grow in a circular pattern around the inside of the pot. Roots also may be j-shaped from hitting the bottom of the pot and turning back toward the surface. When potbound plants are installed in the landscape, the roots will not grow outward unless they are cut and straightened. Instead, the roots will continue to grow as they did in the pot. Eventually, the roots become too deformed to function and the tree suffers from water and nutrient deficiencies. Pot-bound Leylands are more susceptible to winter foliage burn and diseases and will eventually die.

Needle and Twig Dieback

Several fungi, including Cercospora sp. and Pestalotiopsis sp., can cause browning of foliage and dieback of twigs and branches. These fungal pathogens favor moist, humid leaf conditions. Air circulation often is poor in hedge and Christmas tree plantings, providing an ideal environment for fungi to thrive. 

Damage from Cercospora is characterized by leaf browning that begins near the branch base and progresses toward the branch tip. Infections usually begin near the base of the tree. Cercospora infections can be severe and lead to tree death if left unchecked.

Damage from Pestalotiopsis is usually minor and is characterized by brown spots that progress backward from the tip of the needle.  


Space trees adequately. Leylands grow quickly, so consider tree growth when spacing plantings. You can thin dense plantings by removing every other tree. Proper spacing promotes air circulation and reduces stress from root competition. 

Applying a copper fungicide such as Badge SC, Kocide 2000, or SePRO CuPRO 5000 is helpful in prevention, especially when environmental conditions encourage disease. You should apply fungicides every 7 to 14 days from bud break until the new growth is mature. Commercial growers may wish to use azoxystrobin (Heritage) or myclobutanil (Eagle) applied according to label directions.

Canker Diseases

Two cankers occur on Leylands grown in Mississippi: Seiridium and Botryosphaeria. Both cankers are caused by fungi that grow beneath the bark of the tree, disrupting the water flow. Eventually the fungus will completely circle (girdle) the tree. As the canker grows, everything above the canker turns brown and dies from lack of water and nutrients.

Seiridium Canker

Cankers caused by Seiridium unicorne appear on twigs, branches, and the trunk. Cankers are oval-shaped (longer than they are wide), dark brown to purple, and may have small, black pimple-like structures embedded in them. The black structures are the spore-producing fruiting structures of the fungus. Spores produced during moist conditions are spread by water splash and contaminated pruning tools. 

The cankers often ooze resin. Resin flow is less pronounced on older trees or trees in poor vigor. Needles on affected branches become bronze-colored as they die, typical symptoms of water stress.  

Botryosphaeria Canker

Stressed trees are more susceptible to Botryosphaeria canker, caused by Botryosphaeria dothidea. The cankers often are very long, and the surface of the canker may look flat. Fruiting bodies of the fungus are usually evident as black pustules embedded in the outer surface of the canker. Needles on affected branches become bronze-colored. Unlike Seiridium canker, resin does not typically flow from Botryosphaeria canker.


Maintaining vigorous trees is important in preventing both canker diseases. Avoid water and root stresses caused by watering too much or too little, planting too deep, and overcrowding. 

Chemical controls are not available. You should prune infected limbs at least 1 inch below the canker. Sterilize pruning equipment with rubbing alcohol or a 10 percent bleach solution between every cut to avoid spreading the pathogen.

Note: Chemical labels change; always get current information about usage, and examine a current label before applying any chemical. Always follow label directions when applying chemicals.

The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination is intended against other products or suppliers.

Information Sheet 1658 (POD-05-17)

By Clarissa Balbalian, Diagnostic Laboratory Manager, Plant Pathology.

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Portrait of Ms. Clarissa J. Balbalian
Diagnostic Lab Manager
Plant Disease and Nematode Diagnostics

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