APPLES: How to deal with bitter pit in apples

This condition results from low levels of calcium in the fruit, which can be exacerbated when the apples are large or picked too early.

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Bitter pit, which affects apples and, to a lesser extent, pears, was first identified in Germany in the 19th century.

The most obvious signs of this disorder are dark spots, about 0,5cm in diameter, on the skin or in the flesh of the fruit. The cells in these spots are necrotic (dead) and brown-black in colour, and the flesh has a dry, spongy or corky texture and a bitter taste.

Bitter pit is not actually a disease; it is a disorder caused by low levels of calcium in certain parts of the fruit.

NUTRIENTS AND IRRIGATION

Prevention is the key to controlling bitter pit. Your first step is therefore to consult records to establish which cultivars and orchards are more susceptible.

There are three main aspects to managing bitter pit:

• Provide adequate levels of calcium;

• Irrigate regularly;

• Avoid over-thinning the trees, as this may result in large fruit, which can cause calcium to be withdrawn from the fruit or become diluted during fruit growth.

Most mineral nutrients are taken up by the roots of the tree. For this reason, you should ensure that soil conditions are ideal for calcium uptake before planting, and maintain these conditions throughout the life of the orchard.

In addition to this, apply calcium by means of spraying. Give the younger trees smaller applications more regularly, and apply relatively more nitrogen to promote growth, while still maintaining a balance between the nutrients.

When the trees have begun bearing, apply nitrogen and potassium in spring, nitrogen in autumn, and calcium sprays during the fruitexpansion phase. Correct pH and soil phosphorus levels in autumn.