Citrus fruits, most often navel oranges and lemons, can be damaged by a disease called stylar end rot or black rot. The stylar end, or the navel, of the fruit may crack, become discolored, and begin to decay because of infection by a pathogen. Protect your citrus crop by creating an environment for healthy fruit to develop.
What is Stylar End Rot?
Stylar end rot is also called black rot in navel oranges, but is also sometimes referred to as Alternaria rot. The stylar is the end of the fruit that we usually call the naval. When the stylar is cracked or damaged, an infection can get in that causes the damage and rot.
Stylar end breakdown causes include a few different pathogens of Alternaria citri. Unhealthy or damaged fruit is susceptible to the infection. The infection may occur while the fruit is still on the tree, but much of the resulting rot and decay occurs while the fruit is in storage.
Symptoms of Stylar End Rot
Fruit that have been infected with this fungus may start to change color prematurely on the tree, but you may not see the more obvious signs until you have harvested the fruit. Then, you may see darker spots at the stylar end of the fruit. If you cut into the fruit, you will see rot that may penetrate right to the center.
Preventing Fruit with Stylar End Rot
Once you see the end rot in your fruit, it is too late to save it. But, with complete stylar end rot information, you can take steps to prevent the infection. Stylar end rot is most common in fruits that are not healthy or that have been stressed.
If you can provide your citrus trees with the best growing conditions and take steps to manage stress, you can prevent the disease: well-drained soil, plenty of sun, occasional fertilizer, adequate water, and pest control.
Fungicides used preventatively have not been shown to work.
Stylar End Breakdown in Limes
A similar phenomenon is described in limes, in which limes left on the tree too long develop yellow to brown decay at the stylar end. This is not attributed to the Alternaria pathogen. Instead, it is simply over-ripening and rotting. It happens if you let your limes stay too long on the tree before harvesting them. To avoid, simply harvest your limes when they are ready.