Chelate forms of iron have given variable results. Annual applications appear necessary. The avocado is particularly sensitive to salts. It accumulates chlorides and sodium more readily than most other tree crops. An accumulation of chloride manifests itself as a tip and marginal burn of the older leaves, premature defoliation, and sometimes a progressive mottled yellowing behind the burn.
Excess sodium shows up as an interveinal leaf burn along with twig dieback.
A rapid burn of the leaves at the tips or at the base of the leaf followed by defoliation suggests either an excessive fertilizer application or inadequate irrigation. The ranges of elements in avocado leaves have been established ten-tatively, as shown in Table 5. These are useful as guides to fertilization and orchard management, but should not be taken as the absolute values for all varieties under all conditions. Leaf analysis from trees prior to coming into commercial production are more difficult to in-terpret, particularly for nitrogen. In the absence of other deficiencies or excesses, zinc and iron deficiencies may be diagnosed from visual symptoms.