Disorders producing symptoms mainly on recently matured leaves

Deficiencies

Manganese deficiency produces a light green to yellow interveinal chlorosis which appears first on recently matured leaves, but in severe cases it may affect almost all leaves on a plant (Photo 12a).

The chlorosis develops initially at the leaf margins (Photo 12b) and then spreads between the main veins towards the midrib leaving only a small zone of healthy green tissue either side of the veins (Photo 12c). As the deficiency becomes more pronounced, the zone of healthy tissue recedes even further towards the veins so that eventually only the veins remain green (Photo 12d).

Frequently, the tissue between the minor veins is ridged upwards and the affected leaves may have a shiny waxy appearance (Photos 12c and 12d). Leaf size is not noticeably reduced (Photo 12a), nor is there any necrosis of the leaf tissue (Photos 12b and 12d).

Manganese concentrations in fully expanded leaves of healthy plants sampled in the field at mid season usually range from 50-150 µg/g dry matter. It has been found that manganese deficiency can severely reduce fruit yield^4,37. Concentrations of manganese below 30 µg/g dry matter in the youngest fully expanded leaves on non-fruiting canes were associated with large reductions in the number and total weight of fruit per vine.

Manganese deficiency of kiwifruit is widespread in parts of Gisborne and Hawkes Bay and is usually associated with soils which have a pH exceeding 6.8. Under these conditions, the solubility of plant-available manganese is greatly reduced.

In addition to those areas where the pH of soil is naturally high, manganese deficiency has occurred in kiwifruit where excessive applications of lime have been applied to the soil, where vines have been grown on sites of old lime or cement dumps, and on old Maori middens (large accumulations of discarded sea shells) which supply abundant lime in the vicinity of roots.

In most cases, manganese deficiency of kiwifruit grown on high pH soils in New Zealand can be corrected readily by applying sufficient quantities of compounds which will acidify the soil thereby releasing previously unavailable manganese to the plant. Such acidifying compounds include finely ground elemental sulphur, aluminium sulphate, or ammonium sulphate.

The quantities of these acidifying compounds required to lower the pH have been estimated for a range of soil types common in the Gisborne and Hawkes Bay regions¹¹.

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12a	12b
12c	12d