I am located in Los Angeles County about 40 miles inland from the ocean. We have had severe drought conditions until this past rainy season (Nov-March). Of 40 pittosporum undulatum trees on our property, 7 have died in the last 10 months. The foliage on the trees that died started to wilt and then the trees died within 3-4 months. I could not find any evidence of the cankers described in your article, "Botruosphaeria Canker Treatment". Starting in June,'16 I soaker hosed the pittosporum for 36 hours every 16 days. I checked with a soil probe before each watering to make sure the soil has dried from the previous watering. Do you have any suggestions for further preventive treatment? Does watering encourage this fungus similar to what happens with phytophera?
Pittosporum Undulatum Trees
Certified GKH Gardening Expert
From my research the Pittosporum Undulatum is considered quite drought tolerant; especially in older specimen.
If you see no other signs of disease, I would suspect that the plants were effected and died from lack of oxygen--due to the heavy rain and or poor drainage.
Well drained soil is needed for the success of your trees.
Check the soil drainage.
This article will help you.