dessicated and deceased

This is - or rather, was - my beloved avocado tree.  What happened between early October, when I last saw her, green and flourishing, and now?  This would have been her fifth year in the ground - and the one when she had a chance of developing and growing little avocado pears.  I protected her from the sun - hence the strange black net arrangement, looking rather like a decapitated Hallowe'en witch with broomstick.  She had just the right amount of water, I thought.  The answer would seem to be Avocado Root Rot - which doesn't just happen, but is caused by a combination of over-watering, and oomycete, which love damp ground - oomycete being a kind of water-borne mold, with the avocado being assaulted - specifically - by Phytophthora cinnamomi. The Global Invasive Species Database counts Phytophthora cinnamomi in its list of "100 of the World's Worst Invasive Alien Species". These water molds were originally found only in tropical and subtropical countries, but are now found around the world.  And how do they spread?  It seems that - absent other ideas - it's likely through the burying habits of squirrels. Bah.  Where are the Great Horned Owls when you need them?  They were chatty enough during this evening's job talk ...