Q: I have two beautiful, mature Leyland cypresses in my yard. I noticed that their tips are turning brown in spots. I see the same phenomenon on my neighbor’s evergreens that border my yard. Is this a disease? Do the trees need to be treated?
A: The brown tips on Leyland cypresses at this time of year are a symptom of Seiridium canker, a fungal disease. When these trees are stressed due to drought, poor planting techniques, and/or poor drainage, they can be susceptible to disease and insect issues. If the trees are planted too close together, there is a lot of root competition for moisture and nutrients, and the trees will also suffer from a lack of sunlight and poor air circulation.
There is no treatment for Seiridium canker. The brown tips will drop off naturally. Prune any dead branches during dry weather. The best recommendation is to keep the trees well-watered during dry periods. Keep mulch no thicker than several inches deep and away from the base of the trunk. Avoid over-fertilization. Leyland cypresses grow best in full sun with plenty of air circulation and appreciate moisture during dry periods.
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