Q. The fruit on my citrus (especially my navel oranges) is splitting. What is causing this?
A. Fluctuations in the weather, temperature and watering cause fruit split in citrus, especially in navel oranges. A period of high humidity followed by a dry period can trigger the splitting effect. Usually only a few fruit on any given tree are affected. Monitor for extreme or sudden climate changes and keep the soil under citrus trees evenly and consistently moist, not soggy, to alleviate the problem as much as possible. Irrigate when the top 3-4 inches of soil have dried out.
UC Publication 8038 Navel Orange Split