Answer: The pittosporum dieback sounds like a lower fungal stem canker and/or a fungal crown rot. This is an obvious blackened to gray discoloration in the lower stem or crown area of the plant. Infection damages the vascular tissue in that critical area, interfering with the movement of water to the upper portion of the plant, causing limb and branch die back. If the entire crown is involved, the entire plant usually declines and dies. There is no control other than to keep the plant non-stressed and actively growing. Try feeding your pittosporum with a general purpose 10-10-10 and pruning them back a little each spring to encourage healthy new growth. Best wishes with your shrubs.
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