Most citrus fruit diseases are caused by fungal or bacterial infections. Infections can occur when the fruit is mishandled, accidentally poked or cut. This allows infections a way to enter the fruit. Special care has to be used when growing, handling and storing citrus. Proper sanitation is also important to prevent infections. Diseases can wipe out an entire season's crops, financially ruining the farmer and sending citrus fruit prices soaring. Some of the most common diseases are citrus canker, haunglongbing, melanose, brown rot, greasy spot, sooty mold and alternaria fruit rot.
Citrus canker is a bacterial infection that causes yellow blisters, or halos, on the fruit and its leaves. It can also create holes in the leaves. Severe canker causes leaves and fruit to fall off prematurely. It spreads rapidly by wind, birds, insects, clothing and infected equipment.
Huanglongbing is a bacterial infection known as greening disease. It is spread by an insect, the Asian Citrus Psyllid and infects all kinds of citrus trees. It causes the infected tree to yellow and die within a few years after contracting the disease. The fruit is usually bitter and misshapen. Greening is hard to detect because it has the same symptoms as nutritional deficiencies.
Melanose is a fungal infection. It infects all citrus but mostly grapefruit. It affects the appearance of the fruit but not the taste. The disease causes small, brown scabs on the fruit's rind. It occurs only when the fruit is small. Melanose is worse in older trees.
Brown rot is a fungus that attacks fruit on the tree during irrigation or heavy rains. It begins with a white growth on the fruit, along with a strong odor. It later causes decayed spots that are brown and leathery. Fruits on lower branches of the tree are most often infected because the fungus is usually in the soil. Soil mixed with water splashes on the fruit and causes the infection.
Greasy spot and sooty mold
Greasy spot and sooty mold are both fungal infections. They infect mostly the leaves but greasy spot can affect the fruit. Insect secretions cause sooty mold. The mold turns the leaves black. Greasy spot causes the fruit to become spotted and creates blisters on the leaves and leaf drop.
Alternaria fruit rot
Alternaria fruit rot is a fungal disease. The fungus affects mostly lemons and navel oranges. It causes the fruit to prematurely change color. The disease doesn't form until after the harvest and becomes a problem during storage. It causes brown or black spots on the ends of the fruit and rots the inside.