Blossom and fruit drop and fruit splitting are fairly common problems for fruit trees. While losing blossoms and small fruit from your fruit trees can be disturbing it is usually a natural process. Trees which bloom profusely like the mango and avocado could not possibly hold all of the fruit which forms on each limb and so it sheds the excess. You can also remove some small fruits yourself which will increase the size of those allowed to mature. This is actually a good idea for young newly planted trees to allow the tree to use its energy for growth rather than fruit production.
Or other stresses could be affecting the tree. A proper fertilizer program should be maintained throughout the year. With little or no fertilizer the tree will not have the essential nutrients for growth and fruit production. A balanced fertilizer containing the proper micro-nutrients and the basic macro-nutrients should be applied several times a year. When nutrition is responsible for blossom and fruit drop, nitrogen deficiency is usually the problem, although phosphorus and zinc deficiencies can also be a problem. The best way to treat a nutritional deficiency is to prevent it using a fertilizer containing all the elements necessary for proper growth. Look for a fertilizer labeled as a fruit special. This blend will have the micro nutrients necessary for fruit production.
Improper watering is one of the primary causes of blossom and fruit drop. The roots of a citrus tree spread outward, just below the soil surface. The bloom period occurs during the dry season so it is easy for your tree not to receive an adequate supply of moisture. Observing the weather conditions and watering at regular intervals during the dry periods will help prevent fruit loss, not just in citrus but in all fruit trees.
Poor pollination can also cause problems. Often two types or cultivars of a particular fruit tree are necessary for proper pollination. You can check the subtropical fruit literature at the public library to determine whether your tree requires a pollinator or not.
Finally, strong winds will cause blossoms and small fruit to drop. Even mature fruit will fall if the winds are strong enough as those who cleaned up after Hurricanes Andrew and Wilma can attest.
Fruit splitting usually occurs in September and October. This can happen when not enough copper is available to the tree. Splitting also can be a problem when there is an acute deficiency of other fertilizer elements necessary for plant growth. During certain times of the year there may be periods of heavy rainfall or drought. The problem is often accentuated just after a period of moisture stress followed by heavy rains. The tree takes up considerable moisture and forces it into the fruit. As the fruit nears maturity the rind becomes less pliable and fails to expand properly. Some varieties and young trees are more susceptible to this problem than older bearing trees. There is nothing you can do for the current crop. Next year splitting can be lessened by a balanced fertilizer program containing the necessary minor elements and by more uniform irrigation during the fruiting season. You should remove the affected fruit as it can attract insects.
And finally, many fruit trees have a habit of bearing a large crop of fruit one year, while resting with a smaller crop the next year. Keep your trees well fertilized and watered and enjoy the “fruits of your labor”. Sorry I could not resist.