What has happened to the soil around this tree in the last 4 to 5 years? What is the soil like where this tree is growing now compared to what it was like a few years ago?
The vast majority of the time when a fruit tree stops producing and the leaves start to look not too good the reason is found in the soil.

The soil -- nothing in particular. It was planted in 1/2 soil, 1/2 fertilizer, with mulch on top 2 years ago. Since then, we've been fertilizing it with those pellets (for fruit trees) from home depot since then. We've done nothing else to th soil. I've noticed a slightly white film on the mulch that has developed in the mulch/soil around the plant.

Thanks.

1/2 soil and 1/2 fertilizer could be the cause if the fertilizer used was synthetic. The trees roots were burned.