Mark from Las Vegas, Nevada writes
I would suggest inspecting the tree for a sucking pest such as aphids or thrips which produce the by-product of honeydew, which can be confused with sap. Otherwise, we would recommend contacting your local Cooperative Extension and speaking with a Master Gardener or an Arborist who would b more knowledeable about the most common pests or diseases that could cause this problem in your area. You could certainly also look for damage pictures online to try to assist you in identifying the problem.
Answer last updated on: 05/24/2016