Leyland Cypress Diseases

The Leyland cypress (x Cupressocyparis leylandii) has been a popular landscape tree in North Carolina over the past ten to twenty years, especially for screens and hedges. Several diseases affecting them are becoming more common. Many homeowners are now seeing problems with their trees, such as browning or bronzing of the needles. Some possible disease culprits include Seiridium and Botryosphaeria cankers, Cercospora needle blight, and Phytophthora and Annosus root rots.

Cankers

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 the angle between branches. This can cause twig, branch, or — on smaller plants — stem dieback. Cankers appear as sunken, dark brown or purplish patches on the bark, often accompanied by extensive resin flow. Keep in mind that resin can ooze from the branches and stems of otherwise healthy plants of Leyland cypress, thus resin flow by itself does not necessarily mean that a Seiridium canker is present. Look for other signs as well.

Scattered twigs or branches killed by the fungus turn bright reddish brown 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 happen 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 (drought or under watering) 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 one part chlorine bleach to nine parts water. Tools should be cleaned and oiled after using bleach to prevent rusting. Severely affected plants should be removed and destroyed.

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 this disease on Leyland cypress. There are options for general use chemicals on ornamentals.

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 settings. It 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. Nurseries can control the disease by treating with Subdue Maxx fungicide. 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; 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.

Leyland cypress is no longer the tree of choice to plant. There are many other trees that will give privacy screens with fewer disease problems. Before future plantings, investigate trees and their characteristics. The North Carolina State Extension Gardener Plant Toolbox is a great resource at http://plants.ces.ncsu.edu.