Fruit that splits is a problem in many types of fruiting plants, including citrus, blueberries, and grapes. The splitting is often caused by too much rainfall (or irrigation). The symptoms are typically seen when heavy rains (or excessive/irregular irrigation) occurs after a significant dry spell. Although this type of situation is the most common cause of split fruit, it certainly is not the only one. I received a photo this morning showing kumquats that have split open (see photo below). Now, here in Mississippi we have not had any of that significant dry weather recently, but what we have had is a lot of rain — first with Hurricane Isaac and then another 5 inches (or so) this past weekend. What happens is that the flesh takes up water faster than the skin (rind) can accommodate. Fruit types with thin skins are often more susceptible to this problem. Other causes such as insect depredation and nutritional imbalances can also lead to fruit splitting, but are less common than water uptake.