The fungus known as botryosphaeria dothidea has symptoms similar to seiridium canker. Branches will turn yellow to brown in color. However, the needles will not easily fall off by running your hand down the branch. Much deeper cankers will be visible as the tree dies. These cankers are often v-shaped and girdle the branch to kill it on a more rapid level. The affected branches will be darker in color than that of a healthy branch. Botryosphaeria canker will have a dark brown presence when cutting into a branch.
This fungal pathogen quickly disperses throughout the bark and healthy tissue. Raised black dots appear on the top of the canker (only visible with a magnifying glass). These spores are spread by rain and overhead irrigation.
Prevention and Treatment
Remove and destroy infected plants including the entire root system. KnowTrees llc can easily help you determine the problem with your Leyland Cypress and remove it if necessary. There is no practical chemical control for home gardeners. Improve soil drainage by adding organic material to heavy, clay soils and avoid overwatering. If replanting, do not plant a Leyland cypress or other susceptible species where Phytophthora is known to be present.