Trees, Shrubs and Conifers: Palm tree help?, 1 by Chiefengineer

Chiefengineer wrote:
I may be in the wrong forum so maybe someone can direct me.
The attached picture is a washingtonia robusta growing in 9A in a row
of 16 next to my driveway. All the others are perfect, and this one was
one of my best. They are all 5 years old, 2 in the ground. In one day the
whole thing browned and slumped. It was after the first rain in 6 months.

I can find no mold or rot, bugs or disease. Just radical rapid browning.
All the others are green. Even the crown is beginning to brown. It had been
fertilized with palm tree spikes the same as the other trees...being a smaller
tree I cut spikes (maybe root burn?). I sprayed the crown with anti-fungal
agent, flushed the roots, and fertilized with manganese and some time-release
balanced granules. I have never seen anything go down so fast. I have
queens, pindos, and canaries thriving. Anyone know what happened?