The Leyland cypress is a pyramid-shaped evergreen that has become a popular element in landscape design. It averages a growth rate of approximately 3 feet or more per year--making it perfect for windbreaks, hedges and privacy screens. The branches of the Leyland cypress have a soft, feathery appearance, and its needles when broken are extremely fragrant. It is susceptible to two branch and dieback diseases, including seiridium canker and botryosphaeria (Bot) canker. According to Alabama A & M and Auburn University's article, "Canker and Dieback Diseases of Leyland Cypress," "Seiridium canker surfaced in the mid-1920s in California. It has since migrated across the southeastern United States."
The Leyland cypress is a hybrid of the Monterey cypress and the Nootka falsecypress, as noted by Alabama A & M and Auburn Universities. The foliage is dark green in color, and it maintains this color throughout the year. A mature tree can reach a height of up to 70 feet. It prefers an organically rich, moist but well-drained soil to grow in. Leyland cypress has a shallow root system, which does not lend itself to extreme/long-lasting drought conditions. Stressed trees are more likely to succumb to disease, so it is important to maintain a healthy tree. Maintaining a healthy tree begins with proper site selection.
Seiridium Canker Disease
Seiridium canker is a fungal disease, which is caused by Seridium cardinale fungus. You will notice a yellowing or browning of the foliage/needles, which begins on the top/lateral branches of the tree. Usually this occurs during the spring season (although it can happen at any time during the year). This yellowing continues to other branches--killing a large part of the tree.
The fungus enters the tree through branch or twig wounds. Once the fungus invades tree cankers form on the twigs, branches and the trunk. These cankers are lens-shaped and gray in color. It is not uncommon to see resin oozing from the cankers. The fungal cankers also produce fruiting bodies, which appear on the cankers as black dots. These black dots are about as large as a pencil lead.
How the Disease Spreads
The Plant Pathology Extension of North Carolina State University in an article concerning diseases of the Leyland cypress tree discusses how this disease is spread--Seiridium canker is spread by fungal spores. The spores can be spread from tree to tree when it rains or through irrigation. Infected pruning tools are also a means of spreading the disease.
The best control is to maintain a healthy tree, as there are no chemical ways to control seiridium canker. Make sure that the tree receives adequate watering, mulch, and prevent wounding of the tree if at all possible (keep pruning to a minimum). When symptoms of the disease appear, prune the infected branches as soon as possible, and destroy the diseased plant material. Also, disinfect all pruning tools to eliminate spreading the disease via your pruning tools.
Bot canker's symptoms are similar to the symptoms of seiridium canker. Although oozing resin may not be seen with this fungal disease. Spreading of the disease is also very similar. However, bot canker can be distributed by the wind. Control measures are identical.