The early symptoms of faint mottling of young leaves generally appears when plants are half term and intensifies and spreads to the remaining parts lending deficient plants a drab rusty appearance. Deficiencies of this element are comparatively rare. Tomatoes are occasionally affected, the terminal shoots adopting a conspicuous creamy appearance. Magnesium deficiencies are very common overseas where soils have been cropped for a long time but they are rare in NZ where soils have only recently been cropped. Instances are common in tomatoes apparently without detrimental effects.
Older leaves develop interveinal yellow patches which eventually turn brown as the leaves desiccate.
No other cases of deficiency disorders due to this element are known in NZ, though examples are common overseas. Copper deficiencies have occurred in lettuces and onions in peaty swamp reclaimed soils. Sound cultural practices based on observation, experience and planning will in most cases avoid the need for measures to correct a nutritional stress. Prevention is better than cure. Regular applications of commercial fertilisers prevent deficiencies of nitrogen, phosphorus and potassium from occurring, though supplementary dressings at the middle stages of growth beneficial for luxuriant or intensive plantings in the case of nitrogen or potassium.