Brown Rot on citrus trees appears on the fruit as light brown or dark brown spots on the skin. The spots may cover only a small part or almost all of the fruit. The markings appear as serious bruises on the fruit. As the infection progresses, it is common to see mold develop on the brown spots and for the fruit to drop. Leaf and twig die back can also be visible, as well as cankers on the tree trunk from which sticky ooze may seep.
The disease is caused by a fungus which inhabits the earth around the tree. The fungus is part of the Phytophthora species. It is most prevalent in wet soil and during periods of excessive rain. The fungus attacks the fruit as it is splashed up on the tree by rain or irrigation spraying.
To control Brown Rot it is important to remove all leaves and damaged fruit when it falls to the ground; prune off all lower branches of the tree so that the tree branches are more than 2 feet from the ground; spray the tree with a fungicide when the disease is identified and again the following spring to prevent re-infection. There are two fungicides that are recommended to control the Brown Rot fungus: Agri-Fos Systemic Fungicide and Captan Fungicide. Repeat spraying every 14 to 21 days as needed.