Question
I live in east central Pa , have several medium size 25' high mulberry trees (red) . the last few years they have gradually had what appears to be a white substance that covers the the majority of the small branches increase. Nothing on the trunk of tree still fruits canopy has noticably thinned . Appears to be some sort of fungus or mildew any ideas what it might be ?

Answer
Michael:
This white stuff may represent a fungus that is merely present on dying or declining tissues, not as a primary cause, but a secondary or opportunistic organism.  The real source may be some level of decay within the internal portions. You are welcome to send me a closeup photo of this stuff on the twig and I may offer you a suggestion.

Regards
Steve