Growers should fertilize their trees to meet the TOTAL demands of the tree throughout the complete development process. From flowering, fruit set, fruit enlargement, maturity, the next vegetative flush, and especially when a crop remains on the tree during bloom and the fruit set of the next crop. Low biuret urea would help with providing some of the energy the tree needs in producing the carbohydrates (the tree's food) to produce branches, leaves, flowers and fruit. It certainly would not hurt. In order to help, the spray should be made a month before the expected bloom date of your tree, also do not apply the spray directly on the flowers while the tee is still in bloom. I should say at this point that I don't know all that much about the botany and physiology of the particular cultivar Lee x Nova. The problem could be inherent with that particular cross, or it could be that the die off is due for some reason that the tree after producing the present vegetative flush and flowering does not have enough stored carbonates to carry the process to completion or even a variety of other concerns. Always remember foliar sprays do no replace regular fertilization through the root system. If you do apply the low biuret, come back and tell us the results.