Description: Seridium canker is caused by a fungus and is the most damaging disease of Leyland cypress. The fungus will destroy the cypress’ form and eventually kill the tree if not controlled. Symptoms: The most noticeable symptom of Seridium canker is yellowing or browning of the foliage on one or more top or lateral branches. The yellowed foliage is in sharp contrast to the dark green healthy foliage. This discoloration can appear at any time but mostly in spring. Seridium canker often invades the tree through wounds on the twigs, branches and trunk. Fruiting bodies of the canker appear on the bark as small black dots about the diameter of pencil lead. When the bark surface is moist, masses of spores ooze from these fruiting bodies and are washed down the tree or splashed from tree to tree by rain or overhead irrigation. New infections develop when spores lodge in bark cracks and wounds. Action: In residential and commercial landscapes, proper establishment and maintenance are the best defense against Seridium canker. Proper spacing should be maintained when planting to avoid overcrowding, which can help spread the fungus. During prolonged drought, thoroughly soak the soil around the base of the Leyland Cypress weekly. To minimize competition for water between trees and neighboring lawns, use a two inch layer of mulch, extending it several feet past the lowest limbs. Tools must be sanitized between each cut by dipping them in rubbing alcohol or in a solution of one part chlorine bleach to nine parts water. Always destroy diseased plant parts and try to avoid physical damage to plants. There is no cultivar of Leyland cypress that is currently available known to be resistant to Seridium canker. Healthy trees are the best defense. Thank you for reviewing this information. Schneider Tree Care is committed to preserving and enhancing the quality of your property through tree care education and services. We employ professionally trained and certified arborists who are available to meet with you for a consultation at no charge. If you have any questions or need additional information regarding the health of your trees, please contact us.