What is Citrus Alternaria Rot?
Citrus alternaria rot, or black rot, is most commonly found in oranges, tangelos, and lemons. However, it may occur in other citrus as well. During periods of rainy and/or humid weather, a fungus called Alternaria citri may begin to grow on damaged or dead citrus tissues. The fungal spores are then released and are able to spread to citrus blossoms and immature fruits. The spores enter the fruit through naturally occurring cracks early in fruit development and begin to cause rot.
Symptoms of Alternaria on Citrus
In many cases, alternaria of citrus is not discovered until after the harvest. However, there are few key observable symptoms which may indicate a cause for concern. Some fruits may show early signs of infection, such as premature coloring, while others may not show signs of rot until after being stored. Infected fruits that have been stored may begin to develop brown or black spots at the bottom of the fruit. Slicing into the fruit will reveal even further damage. A citrus tree with alternaria is also much more likely to drop fruit before it has ripened.
Preventing Citrus Alternaria Rot
While there are some treatments available for commercial growers for fruit post-harvest, the best option for the home gardener is prevention. Unhealthy, stressed citrus trees are far more likely to have issues with alternaria of citrus. To prevent black rot on citrus trees, maintain a proper care schedule which includes watering and fertilizing regularly.
