In both avocado and citrus there can be a rapid collapse of tissue brought on by a host of related fungi. The pathogen was once lumped as Dothiorella, but lately University of California extension plant pathologist Akif Eskalen has been able to tweeze out more species which mainly belong to the Botryosphaeria genus. The collapse can be quite rapid, so fast that the leaves continue to hang on to the tree. This disease is more common in years of low rainfall, where inadequate water is being applied (especially when Santa Ana winds are blowing), and where salinity build up has occurred. In the last 2 months, I have been called out to diagnose this problem five times. In each case, they were trees that had been sidelined and neglected or the grower was trying to save money by saving water. Luckily for a mature tree, there can be recovery as long the tree is protected from sunburn that occurs with defoliation. White wash the exposed parts, and wait for recovery. When it is clear what part is recovering, cut into fresh wood to remove the dead parts. For a more detailed discussion of this blight, see our 2009 Topics in Subtropics.
Stem and Leaf Blight
Jun 15, 2012