Leaf curl of orange trees can be caused by insects or overwatering. It is normal for leaves to curl downward in the late fall and early winter.
Aphids, citrus thrips and citrus whiteflies feed on soft, new leaves in the early spring and throughout the growing season. Signs of these insects can be found inside the curls of the leaves. Overwatering can also cause the leaves to curl inward. The leaves then turn yellow and drop. If overwatering is continued, the tree may die. Very hot temperatures can cause leaves to curl inward, and very cold temperatures can also cause the leaves to curl. Orange trees should be covered if freezing temperatures are expected.