What is the role of boron in apple production?

Boron is responsible for pollen germination and pollen tube formation and activation. Thus, poor boron supply results in poor flower and fruit formation. In severe cases, it causes ‘blossom blast’ where flowers dry out and are shrivelled at bloom.

Boron effect at growth stages

Boron deficiencies in apples

Symptoms are frequently found in the fruit with little sign of deficiency in the leaves unless the deficiency is severe.

The most common symptom in apples is small, clear, water-soaked areas in the flesh of the fruit. These may dry out, turn brown and leave spongy lesions in the fruit.

In some cases, deep cracks in the skin may occur. The skin is rough and heavily russeted.
When boron deficiency occurs in combination with a lack of calcium, the fruit is of poor storage quality and bitter pit is more common.

In severe cases, dead areas appear on the bark of young branches (apple measles).
Boron toxicity results in chlorosis of leaf margins and tips, followed by necrosis. In fruit, high levels lead to a reduction in storage quality – fruit softening.