What is the primary cause of internal cork disease in apples?

The primary cause of internal cork disease in apples is linked to calcium deficiency rather than magnesium deficiency. Internal cork is a physiological disorder that often arises when there is insufficient calcium available to the apple tree, which is essential for maintaining cellular structure and plant health. Calcium plays a critical role in the development of cell walls; without adequate calcium, cells can weaken and become more susceptible to disease and disorders.

When the trees experience calcium deficiency, it can lead to necrosis of the cortex tissue, resulting in the characteristic corking symptoms that manifest inside the fruit. In many cases, the observed corking correlates with periods of rapid fruit growth that may outpace the tree's ability to uptake calcium from the soil.

While magnesium, potassium, and iron deficiencies can cause other physiological disorders in plants, they are not the direct cause of internal cork disease. Each of these nutrients serves different roles in plant health: magnesium is crucial for photosynthesis, potassium regulates various metabolic processes, and iron is essential for chlorophyll production. However, in the context of internal cork disease specifically, calcium deficiency stands as the primary culprit.