There are a number of reasons why a deciduous fruit tree may not produce fruit. The ones that we have identified as possibly pertinent to your situation are as follows: It could be incomplete pollination if the flowers are not falling off. If the flowers are shriveling and dying on the tree then there is a pollination problem. However, you stated that there are bees around and trees adjacent to this one that produce so this seems less likely. Nectarines are self-fruitful and do not require a pollenizer tree. The tree may require more chill hours than Tucson gets - perhaps it was mislabeled when you bought it. Many nectarine varieties require 600 to 900 chill hours but Tucson typically gets 350. If you know the variety name we can look up its chill hour requirements. Fertilizing with too much nitrogen or at the wrong times - but that would seem to affect adjacent trees so that may not apply. Over fertilization stimulates excessive growth at the expense of flower production. Possibly the tree is sterile and just doesn't produce fruit - we don't know why this happens but it seems to happen sometimes. We simply get a tree that doesn't produce. Then your dilemma is whether to keep it for beauty or replace for production.