Orange trees are prone to numerous problems, including pests, diseases, nutrient deficiencies and other disorders. You can avoid some of the problems with the proper planting procedures, irrigation and fertilization. Orange trees should be planted in the full sun in well-drained loamy soil and be spaced far enough apart to allow good air circulation. Fungicides and pesticides for orange trees applied at the schedule and rate recommended by the manufacturer can prevent or control some diseases and pests.
Aphids, fruit flies and scale insects attack orange trees, but normally do not cause serious damage to the foliage or fruit. Asian citrus leafminers and citrus psyllids attack the new flushes of growth, which happens four times a year. Young trees may be stunted, but mature trees are usually not damaged.
Indications of pest infestations include distorted or curled foliage, twig dieback, discolored foliage or fruit, and general decline of affected trees.
Some diseases affect the appearance of the foliage and fruits of orange trees, and may reduce the amount of fruit produced. Leaf and twig blights, twig dieback, cankers and defoliation are some symptoms of diseases that affect orange trees.
In extremely wet and warm conditions, brown rot can cause premature fruit drop.
Other diseases cause sunken spots or corky growths on the oranges. Sooty mold is a fungus that grows on the honeydew secreted by aphids on the leaves and small twigs. Fungal diseases also cause discolored or greasy spots on the leaves.
Orange trees need the proper amount of nutrients to grow and bear fruit. Discolored foliage and fruit problems are common symptoms of nutrient deficiencies. A lack of potassium can cause the fruits to develop thin skins that split, or cause premature fruit drop.
Pale green leaves indicate a lack of nitrogen, while light green foliage that is almost white indicates a lack of iron. Lack of manganese causes the tissue between the veins of the leaves to turn yellow. Zinc deficiency causes the leaves to turn light yellow to white with green bands along the midribs and main veins. A lack of magnesium causes irregular yellow blotches on the foliage.
Environmental stresses can also affect the health of orange trees. Fruits that have been damaged by insects or other means may drop prematurely.
Drought or temperatures in the low 20s can cause leaf and twig damage. The fruits will freeze if the temperatures drop below 27 degrees for more than 3 to 5 hours.
Oranges that are exposed to direct sunlight for prolonged periods will scald and develop dried areas of peeling and pulp. Sunscald is more common in thin-skinned fruits. High temperatures and humidity can cause the skin of oranges to split.