Disorders producing symptoms mainly on the older leaves

Toxicities

Excess nitrogen readily reduces the growth of kiwifruit (Photo 10a). Symptoms appear first on the older leaves as an interveinal scorching which spreads from the leaf margins towards the midrib (Photo 10b). Leaves on affected plants are very much darker green than usual.

As the disorder becomes more pronounced, the leaves lose turgor and become very limp giving the plant a wilted appearance (Photo 10a). In the field there may be an upward rolling of the leaf margins (Photo 10c). In this respect, the symptoms are similar to those produced by potassium deficiency. However, an important point of difference is that no interveinal chlorosis develops on plants affected by excess nitrogen.

Nitrogen concentrations in fully expanded leaves of healthy plants sampled in the field at mid season usually range from 2.2 to 2.8 per cent of the dry matter. Results from the solution culture experiments and analysis of leaf samples taken in the field, indicate that symptoms of excess nitrogen do not usually appear until the concentration in the youngest fully expanded leaves exceeds 5.5 per cent of the dry matter. However, it should be noted that it is usual for leaf nitrogen concentrations to exceed 6 per cent of dry matter shortly after bud break, and at this early stage these high nitrogen concentrations fall rapidly to a level which remains relatively constant from December to the end of the growing season.

While excess nitrogen is not a common disorder of kiwifruit in New Zealand, it occurs most often when large quantities of nitrogen fertiliser are banded close to the plant. For most situations, it has been recommended that nitrogen fertilisers should be broadcast over the entire orchard³⁶. For further information on nitrogen fertilisers see section on nitrogen deficiency.

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10a	10b	10c