I have a nine-year old leland cypress. It is planted about four feet from a lake and gets good sun. A few months ago, portions of the tree branches began to turn a rust color and die. It appears to be spreading throughout the tree. I took a sample and pictures to the St. John’s Agricultural Center and was told that leland cypress trees begin to die at about eight years old. Upon some internet research, I did not find any info that confirmed that. I did find that there were two cankers that can affect the tree. I also noted that there is no known cure or control for them. An arborist told me that it should be sprayed with horticultural oil. I don’t know if I should have the tree removed or if there is some way to save it. Can you help me?
Branch dieback on leland cypress is commonly caused by canker disease and this is the likely causal agent for the problem on your trees. Trees that are stressed by drought or excess soil moisture are more susceptible to this disease. We also find that trees that have been planted too deep and have soil over the top of the root flare are more prone to disease.
Pruning out diseased branches and identifying and correcting any stress inducing factors will help prevent further decline. Many homeowners choose to replace leland cypress with more durable species. I recommend that you consult a local arboretum/botanical garden for suitable replacement species.
Horticultural oil will not help the situation unless there is an insect infestation present that is causing plant stress. Leyland cypress can be infested with spidermites and scale insects that can be suppressed with properly timed treatments of horticultural oil.
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