· Brent Wilson's Answer
· It could be seiridium canker...the most damaging disease of Leyland Cypress. I think this disease is caused by poor air circulation and high humidity that becomes trapped in the interior of the trees...when trees were planted and are growing too close together. Many folks bought small leyland cypress, a foot or two in height, and planted them 3 or 4 feet apart. Eventually, the cypress trees become seriously overcrowded and the trapped humdity leads to the onset of Seiridium unicorne, a fungus that leads to Seiridium canker. Leyland Cypress should be spaced a minimum of 8 to 10 feet apart.
The cankers 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. It's the scattered twigs or branches killed by the fungus that turn bright reddish brown, and are in striking contrast to the dark green healthy foliage, that indicates the presence of the disease.
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. As Brooks said, if you catch it soon enough, affected stems, twigs and branches can be removed in an attempt to save the tree and prevent spread of the disease.)