Why Are Orange Tree Leaves Yellow?

Identification

• Orange trees are susceptible to phytophthora root rot caused by Phytophthora parasitica and P. citrophthora. The fungus infects and destroys tree roots. The disease is most common in citrus trees growing in overly moist soils and during cool weather.

Damage

• As the fungus starts to rot the roots, affected trees start to go into a steady decline. Foliage discoloration is among the earliest symptoms characterized by the light green to yellow leaf color. This is accompanied by leaf drop. Fruit production is reduced and roots become soft. The tree's reserve energy store is depleted.

Control

• Avoid overwatering trees and improve soil drainage. Use resistant varieties including trifoliate orange and sour orange. Chemical control options include chloropicrin, mefenoxam or fosetyl-al.