Determine how much boron the soil amendments you use may contain. Pit gypsum can have varying quantities of boron in it. A ton of this gypsum may contain as much as 20 pounds of boron. Actively growing, vigorous trees may dilute the concentration of boron in the leaf tissue through the production of a thick canopy. Old leaves tend to accumulate boron and drop.
Adequate nitrogen ensures that nitrogen is present for production of new leaves.
Increasing the nitrogen fertilization rate can encourage vegetative production and enhance this effect, but too much nitrogen may be associated with adverse fruit quality characteristics like regreening of Valencias, later maturity of early navels or higher yields of smaller fruit. Keeping other nutrients in the leaf in balance is important if boron is present at excessive concentrations. Maintaining high concentrations of phosphorus and calcium in the leaves through an appropriate soil fertilization program should be beneficial as these nutrients have been shown to reduce absorption of boron.