Disease of Leyland Cypress

Mike Benson, Plant Pathologist
Larry F. Grand, Plant Pathologist
Ronald K. Jones, Professor Emeritus

[Seiridium Canker] [Botryosphaeria Canker] [Cercospora Needle Blight] [Root Diseases]

Leyland cypress (x Cupressocyparis leylandii) has become increasingly popular as a landscape tree in North Carolina, especially for screens and hedges. Although relatively free of serious disease problems, several diseases are becoming more common. These include Seiridium and Botryosphaeria cankers, Cercospora needle blight, and Phytophthora and Annosus root rots.

Seiridium Canker

Seiridium canker, caused by Seiridium unicorne, is probably the most damaging disease on Leyland cypress. Plants of all sizes and ages are affected. Cankers may form on stems, branches and in branch axils causing twig, branch or, at least on smaller plants, stem dieback. Cankers appear as sunken, dark brown or purplish patches on the bark, often accompanied by extensive resin flow. It should be noted that resin exudation often occurs from the branches and stems of otherwise healthy plants of Leyland cypress thus resin flow by itself is not a diagnostic characteristic for Seiridium canker. Scattered twigs or branches killed by the fungus turn bright reddish brown, and are in striking contrast to the dark green healthy foliage. Fruiting bodies of the fungus appear on the bark surface of the cankers as small circular black dots barely visible to the naked eye. Spores of the fungus are spread to other parts of an infected tree, or from tree to tree by water splash from rain or irrigation. The fungus also can be spread from tree to tree on pruning tools. Long distance spread appears to be through the transport of infected cuttings or plants.

Currently there are no chemical control measures recommended for the disease in the landscape or nursery. Avoiding water stress and tree wounding may reduce infection. Infected branches or twigs should be pruned and destroyed as soon as symptoms are noted. Prune at least one inch below the canker, and sterilize the pruning tools between cuts by dipping them in rubbing alcohol or in a solution of 1 part chlorine bleach to 9 parts water. Tools should be cleaned and oiled after using bleach to prevent rusting. Severely affected plants should be removed and destroyed.

Botryosphaeria Canker

The outward symptoms of Botryosphaeria canker, caused by Botryosphaeria dothidea, are similar to those of Seiridium canker; that is, scattered bright reddish-brown dead twigs and branches occurring in otherwise healthy foliage. Cankers on small twigs and branches are also similar to those caused by S. unicorne, except that extensive resin exudation usually does not occur. Unlike S. unicorne, however, B. dothidea may produce long, narrow cankers on the trunk that might extend for a foot or more in length. These cankers rarely girdle the trunk, but will kill any branches that may be encompassed by the canker as it enlarges. Fruiting bodies of the fungus, perithecia and/or pycnidia, are produced just beneath the bark, but their presence can be discerned as tiny raised pimples scattered over the surface of the canker. Spread of the fungus is similar to that described above for S. unicorne, except that ascospores of B. dothidea may be spread by wind.

Botryosphaeria canker most often occurs on plants that are under considerable stress, and an effective control strategy should include keeping the plants growing as vigorously as possible. Mulch plants yearly and provide adequate water during extended dry periods. Avoid heavy fertilization and severe pruning of established plants. Prune out and destroy dead branches. Effective chemical control is not available.

Cercospora Needle Blight

Cercospora needle blight, caused by the fungus Cercosporidium sequoiae (syn. Asperisporium sequoiae; Cercospora sequoiae), is a relatively new disease on Leyland cypress. However, it a common disease on species of Juniperus, Thuja, Cupressus, Taxodium, Cryptomeria, Sequoia and other genera. The first symptom of Cercospora needle blight is a browning of the needles in the lower crown next to the stem. The disease slowly spreads upward and outward until, in severe cases, only the needles at the tips of the upper branches remain green. In a general way, these symptoms mimic those caused by severe stress where the interior needles turn yellow and fall off. Fruiting bodies of the fungus appear as tiny, greenish pustules on the upper surface of the needles or on small twigs. Spores (conidia) are present throughout the spring and summer and are spread by wind. Infection usually occurs during periods of wet weather.

Cercospora needle blight can be controlled by spraying with copper-containing fungicides. There are no fungicides registered specifically for the disease on Leyland cypress, but Kocide is registered for general use on ornamentals. Spray plants at 10-day intervals from bud break until new growth matures.

Root Diseases

Two root diseases may affect Leyland cypress; Phytophthora root rot caused by Phytophthora cinnamomi, and Annosus root rot caused by Heterobasidion annosum. Phytophthora root rot can be a problem in both the nursery and landscape, and primarily affects smaller roots on plants. Large established trees in the landscape are rarely affected by Phytophthora root rot. The disease is usually more damaging in situations where soil drainage is very poor. Plants with severe root damage may exhibit a general yellowing of the foliage and some tip dieback. Phytophthora root rot can only be diagnosed with certainty by laboratory analysis of affected roots. Control of the disease in nurseries can be obtained by treatment with Subdue Maxx. Chemical control is not recommended for landscape trees.

Annosus root rot is usually associated with landscape plants. Initial infection by the fungus is by spores on the freshly cut stumps of conifers, most commonly pine. The fungus grows through the stump and its root system and may infect adjacent trees through root contact. The larger roots of the newly infected plants are killed and decayed. Top symptoms may include a yellowing and slow decline, followed by death of the tree; or the foliage on the entire tree may suddenly turn a reddish-brown color. Some trees may fall over before any crown symptoms are present. Fruiting bodies of the fungus may form at the base of the tree, usually beneath the mulch or leaf litter. These are usually small, irregular in shape, brown on the upper surface and white on the lower surface. There are no effective control measures once the tree is infected. As a preventative measure, stumps of felled, living conifers should be either removed completely, or the stump surface treated with dry granular borax immediately after the tree is felled.

Other Links

Plant Disease Information Notes Home Page
North Carolina Insect Notes
North Carolina Agricultural Chemicals Manual
CALS Home Page
NCCES Home Page

Published by North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

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Webpage revised March 2001 by A.V. Lemay