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DEFICIENCIES

Calcium

Photo 16a (26K)

Photo 16b (13K)

Symptoms of calcium deficiency first appear on the immature leaves of the plant. The symptoms include a yellow-brown interveinal chlorosis, downward cupping of the leaf, and a thickening of the tissues of the blade (Photo 16a). The leaf also becomes brittle and malformed (Photos 16a and b). Die back of the leaf tip and margin results in a tearing of the leaf blade midway along its length (Photo 15b). Soon after the appearance of these symptoms the terminal bud dies inducing the auxiliary buds at the junction of the petiole, and the stem to develop (Photo 16b). Stem lesions may also occur on seriously deficient plants.

The concentration of calcium in the leaves showing severe symptoms ranged from 0.1 to 0.6% dry matter.

Iron

Photo 17a (18K)

Photo 17b (20K)

Photo 17c (18K)

Iron deficiency is characterised by a distinctive change in colour from snow white of the youngest leaves, through yellow, to near normal green of the oldest leaves (Photo 17a). At first the main veins on the youngest leaves remain light green but later even these may become chlorotic (Photo 17b). At this stage large dark brown necrotic patches quickly develop between the main veins on the recently matured leaves (Photo 17c). Occasionally, distinctive bands of green tissue may remain on either side of the main veins of the more mature leaves. Iron deficiency severely restricts growth.

The concentration of iron in the leaves showing symptoms ranged from 30 to 65 ppm dry matter.

Boron

Photo 18a (19K)

Photo 18b (17K)

Photo 18c (14K)

Photo 18d (13K)

Death of the growing tips is the first visible symptom of boron deficiency (Photo 18a). The youngest leaves develop a khaki-yellow chlorosis over most of the leaf except a small zone either side of the main veins. These symptoms quickly spread to most other leaves on the affected plant. Irregular brown necrotic zones develop on the most chlorotic tissue giving a scorched appearance to the leaf. Boron deficient leaves are abnormally thick and leathery in texture, as well as being shiny. Affected leaves may be more rounded in shape than normal (Photo 18b). In severe cases of this disorder, stem lesions may occur (Photo 18c). Deficient plants are also likely to be stunted due to a reduction in the elongation of the stem (Photo 18d).

The concentration of boron in the leaves showing symptoms was 15 ppm dry matter.

TOXICITIES

Zinc

Photo 19a (14K)

Photo 19b (9K)

Photo 19c (15K)

The youngest leaves are the most affected by a toxicity of zinc. A distinctive feature of this disorder is that while most of the leaf tissue becomes chlorotic, the veins remain dark green (Photo 19a). There is also a distinctive pink discoloration of the youngest developing leaf which disappears as it matures (Photo 19a). Irregular patches of necrotic tissue may appear on the more mature leaves (Photo 19b). The oldest leaves usually remain green but necrotic lesions may develop on the main veins, particularly along the midrib; the tissue between these veins may also be slightly ridged upwards (Photo 19c).

The concentration of zinc in leaves showing symptoms was in excess of 1800 ppm dry matter.