Dead Leaves on an Ornamental Orange Tree

Parasitic Disease

• Phytophthora foot rot, or Phytophthora gummosis, is produced by two species of soil-borne fungi. As it affects the inner bark of the orange tree, it restricts the ability of the specimen to circulate water and nutrition to the leaves properly, resulting in dead leaves and premature defoliation.

  Hendersonula Branch Wilt, also called sooty canker or limb wilt, invades the tree through wounds in the citrus bark. As it spreads through sapwood, leaves turn brown, wilt and die.

Virus Disease

• Citrus Tristeza Virus is a lethal disease that initially displays as a yellowing and distortion of citrus leaves, followed by a girdling, or strangling, of infected twigs and branches that leads to the death of leaves and often the entire tree.

  A virus called Stubborn disease affects North American trees exclusively in hot, dry areas of California and Arizona, but has not been found in Texas or Florida. It may severely damage or kill leaves but normally is not fatal to the tree.

Citrus Nematode

• The citrus nematode, or Tylenchulus semipenetrans, feeds on the root system of an orange tree, damaging it to the extent that the roots are unable to absorb sufficient levels of water and nutrients. Previously healthy trees may suffer only a slow decline with symptoms requiring significant time to manifest. Those symptoms display as a yellowing of leaves and their premature death followed by defoliation of the tree. This normally shows in the upper branches of the tree first.

Drought and Freeze

• Water stress caused by drought or improper irrigation of the ornamental orange tree is a common reason that leaves will die. Defoliation and dieback occurs following long periods of drought and hot, dry winds exacerbate this. Temperatures in excess of 110 degrees Fahrenheit cause significant sunburn damage to leaves. Water loss and water usage are dictated by the species of orange tree and the environment in which it exists. Meanwhile, freeze damage will also manifest in the spring or summer as dead leaves.