[Arid_gardener] Question from Home-Hort WWW page

[styrrel at cox.net]

85281
styrrel at cox.net

I have a dieing palo verde,precox. 
The symptoms are no leaves, no flowers and the tips of entire tree dieing back three to four feet from outer edge.  
I planted it almost 20 yrs. ago from a 5gallon container. It is in a desert yard. It gets water every 2 weeks in the summer and once a month in the winter IF we don't get rain. I don't fertilize it. I have seen an OCCASIONAL p.v. beetle over the years but there are no signs of holes under the tree for these to have exited. The truck is still green and branches to about 2" diameter. There has always been a scaly crust on the bark, this can be rubbed off and in appears ramdumly throughout the tree. There are no open wounds or sap ozzing from tree.  
There are many plants in the vicinity that seem to be fine.
I can't think of anything else to add that might give a clue. I've asked several nursery people and the only suggestion I received was possible gumosis but there is no sap bleeding. 
Thanks for your help.