Answer: I'm sure you appreciate how difficult it is to diagnose a problem without seeing it, but Cupressocyparis leylandii, the Leyland Cypress is subject to two common problems, one a disease and the other is an insect. Here's the rundown on both problems: CYTOSPORA CANKER (Cytospora cenisia ) Symptoms: Girdling cankers on branches. Young branch cankers are smooth, reddish brown, and slightly constricted. Foliage on girdled branches turns yellow and finally brown. Control: Avoid wounds. Prune out diseased branches in the dry season, cutting well below visible infection (6 inches where possible). Remove and shred (chip) prunings; dispose of prunings away from cypresses. The cypress tip moth feeds on a wide variety of cupressaceous trees but most notably on Lawson cypress, Leyland cypress, Monterey cypress, Italian cypress, Oriental cedar and some species of juniper having scalelike leaves. Other closely related species of the genus Argyresthia also cause similar damage to these and other cupressaceous trees. Summer and fall feeding larvae hollow out and kill individual scale leaves, but more severe damage occurs during early spring when entire twigs and branchlets are mined. Repeated heavy infestations may eliminate any apparent growth. Heavily infested trees suffer considerable dieback, imparting a scorched appearance to the foliage. Trees are seldom killed but their attractiveness is marred. If neither of these descriptions matches the symptoms, why not take a sample of the problem to your local Cooperative Extension office? If OSU has ruled out pathogens, perhaps they were not looking for insect activity. A third possibility is a root problem, obviously affecting only part of each plant. Hope some of this information will head you in the right direction and you can discover what the problem is! Best wishes with your landscape!
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