Florida orange trees require routine care to maintain tree health and fruit quality. Homeowners and growers must monitor insect levels and look for three main types of disease that affect all kinds of orange: environmental, fruit disease and leaf disease. Most disease can be treated once diagnosed, and Florida's common orange tree diseases are easily distinguished from one another.
Florida orange trees experience two types of environmental disease that can be prevented with proper planning and care: sunburn and root rot. Sunburned trees have peeling fruit and their interiors dry out, reducing the quality of the orange crop. Thin-skinned orange trees are more susceptible, especially when exposed to sun at all times. Consider planting trees in dappled shade or avoiding thin-skinned orange varieties.
Root rot occurs when trees are planted in poor-draining soil. Amend boggy or clay soils, or plant orange trees in containers to ward off this disease.
The most commonly occurring leaf disease in Florida is a fungi known as Alternaria brown spot, which hits oranges and tangerines. Affected leaves develop yellow discoloration and dark brown spots; they may eventually fall from the tree. As the disease worsens, fruit can develop brown spots on its skin. Growers should use copper fungicides to treat Alternaria brown spot.
Greasy spot also affects oranges, notably the Valencia, Pineapple and Hamlin varieties. Affected leaves appear greasy due to blisters; they also turn yellow and can fall off the tree. Copper fungicides and horticultural oil combat greasy spot.
Citrus scab is the major fruit disease in Florida, affecting oranges and other types of citrus trees. Fruit develops pink or brown scabs that turn yellow or gray and develop a bumpy appearance. Severe scabbing can distort the fruits' appearance; affected fruits are not commercially viable because of their disfigured, diseased appearance. Growers can use a copper fungicide to control this disease.
A symptom of severe aphid or other insect infestation, sooty mold grows on fungus produced by the slime these insects leave behind. The result is fruit that looks like it's been rolled in soot, giving the disease its name. Gardeners can remove the mold coating with horticultural oil, which will also reduce the insect population. Monitor pests to avoid a buildup of sooty mold, and treat pests before infestations become serious.
Gardeners should provide Florida orange trees with adequate care year round to cut down on the likelihood of orange tree disease. Pruning dead or damaged wood and removing excess growth so air circulates through the tree can push out fungus and bacteria, eliminating infection. Growers should rake up fallen, diseased leaves to avoid contaminating other trees. Fertilize the orange trees regularly, using an appropriate dosage for the trees' age, to help keep citrus trees healthy. Provide adequate water to avoid stressing the tree. Water the tree when the soil becomes dry and crumbly, and fertilize following the suggested type and amount for your trees' age, using the University of Florida's fertilizer guidelines.