Damage to avocado tree
Please help. What is the cause of this white, powdery substance on branch?
Certified GKH Gardening Expert
That is one of countless "White Rot" fungi! They are very hard to ID without seeing the fruiting body in question. Leaving it can harm the tree in the case of a parasitic fungus, or if it is simply needing a host and is not detrimental, then it will cause no harm.
Since it is very difficult to pin down without a fruiting body, it is best to assume that it will kill your tree.
I would remove the infected branches, and treat with a fungicide to be safe.
This article will help : https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
This University website will explain further: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74109.html