Ask Extension

Granulation usually occurs on rapidly growing fruit and excessively large fruit. While Valencia oranges are most frequently affected, other oranges, grapefruit, and tangerine cultivars are subject to this malady as well, especially when budded on rough lemon and trifoliate orange rootstocks. Good fertilization and nutrition practices and early seasonal harvesting may help alleviate this problem

1. An excess of potassium or nitrogen in the fertilizer might be the cause. Both are essential for normal growth, but too much of either can cause dry fruit.
2. Lack of irrigation and/or rainfall.
3. Minor element deficiencies, especially zinc, iron, and manganese. The soil pH may be too high making these elements unavailable.
4. Fruit is overly mature. Harvest earlier next year.

Additional Resource 

http://edis.ifas.ufl.edu/HS122

 

.