How was the weather before this happened? Did you have hot, dry winds? Any severe temp. changes?
Avocado trees are self thinning. Its probably a natural thing. The new leaves makes me think this.
Remember, water sparingly.
Read the CRFG and Perdue Univ. web sites. It should give you more info. E-mail the CRFG people. They are good, knowledgable people and will help you.
You don't mention where in SoCal your located. If your in the desert area, you might contact CRFG in Phoenix.
I hope this will help you,
John

i grew a 3ft avocado tree from a pit. it was doing great while i lives in california then i moved out to nebraska and within days all the leaves fell off and died and now the tree just sits there looking like a skeleton. when i 1st got to nebraska it was below freezing so i kept it in the garage, then it looked like it died now the temp is up and iwater it and it gets tons of sun everyday and still nothing. and also all over the tree, like on the branch times there is some sort of white powdery stuff. what is that? did my tree die? or isthere something i can do for it???