Why Are Leaves Falling Off Citrus Trees & Twigs Dying?

Hendersonula Branch Wilt

• Hendersonula Branch Wilt, also known as sooty canker or limb wilt, is brought on by a pathogen, Hendersonula toruloidea, and only affects citrus trees that have experienced injury to their bark via mechanical devices, freeze damage or sunburn. The fungus causes a sooty canker underneath the tissue of the bark that leads to the leaves of the tree turning brown, wilting and dying. The branches die back to the canker area with the dead sections falling to the ground.

Wood Rot Fungus

• Wounds to the tree also make citrus more susceptible to two wood rot diseases caused by the fungi Antrodia sinuosa and Coniophora eremophila. These pathogens cause branches on lemon trees to die and fall off as the wood of the branches and twigs is weakened by the rot from within. Before falling to the ground, twigs will often crack open, displaying a white fungus if the tree is infected with the Antrodia disease; however, citrus trees afflicted with Coniophora will not display any white fungal material.

Citrus Nematode

• The citrus nematode, Tylenchulus semipenetrans, infests 50 percent to 60 percent of citrus-growing areas in California and Florida and 90 percent in Texas and Arizona, reports the University of Arizona. The nematode is responsible for the slow decline of the citrus tree -- infected specimens may appear healthy for several years -- as it gradually attacks the root system of the tree and reduces its vigor. Leaves will yellow and begin to fall from tree, cascading first from the upper branches of the citrus.

Leaf Drop and Environment

• Some instances of leaf drop in a citrus can be chalked up as a normal phenomenon. The citrus is an evergreen specimen and sheds leaves slowly -- and naturally -- throughout the year, replacing them just as gradually. This physiological event happens most often during the spring. Citrus trees are also especially susceptible to water stress -- often exacerbated by hot, dry winds. An extended drought will lead to premature defoliation of the citrus tree.