What kind of foliar feed?

this year you added extra fertilizer, could be over fertilization which stressed the tree and cause it to drop all the fruit.

have you noticed any bugs, or tiny insects, etc?

here's something i found

"Certain insects that feed on citrus trees can cause fruit drop. For example, leaf-footed bugs inject an enzyme into citrus fruit causing a tree to lose most of its fruit in a very short period of time, according to a Texas A&M University System Agricultural Program report.

Read more: Why Do Citrus Trees Drop Fruit? : eHow.com http://www.ehow.com/facts_5768931_do-citrus-trees-drop-fruit_.html#ixzz1OUPPuQpM
"

Thanks for the insights. The foliar feed I've been using is Spray-n-Grow, and it seems to be doing great for the foliage and certainly seemed to have boosted blooms on it.

I've seen no insect damage at all but it could have been too much fertilizer combined with early heat stress as this has been a record-breaking hot Spring.