In the fall of 2016 growers in the Coachella desert have been experience very puzzling symptoms on their grapefruit trees. One incident, symptoms the tree had gumming oozing from the branches (Fig. 1). Usually if it were oozing from the stump it would be a root disease such as Phytophthora spp. After photos and branch samples were taken to the Plant Pathologist at University of California, Riverside, Dr. Akif Eskelan, results determined that the trees had branch canker and Hendersonula Disease.

Symptomology

Infection by Nattrassia mangiferae (Hendersonula toruloidea) causes bark cracking and peeling or dead bark that remains tightly attached to dead limbs. Black, sooty growth may develop beneath infected bark. Brownish moist areas appear on limbs during the first stages of disease, then the bark in these areas cracks or peels away revealing black masses of fungal spores (Fig 4.). In advance stages, the injured limbs may “bleed” profusely, oozing a sap like sticky

 substances (fungal spores) (UC IPM 2017). Leaves on infected limbs suddenly wither, turn brown, and dry up. This may ad to the ends of the branches getting sunburned (Fig. 2). However most dead leaves typically remain attached to the twig. Black sooty spores that can survive for long periods under hot dry conditions are spread by wind or rain throughout the year. The disease, however, can only develop under warm temperatures growing best at 90^oF. The southwest side of the tree is the most likely place to find branch wilt because of a higher frequency of sunburn injury.

 

 

 

 

 

 

Management

Trees weakened by a disease, water stress, nutritional deficiencies, excessive pruning/mechanical damage create a are more susceptible. As many of these stressors can cause a tree to get sunburned and creates wounds that can serve as infection sites for this pathogen.  Prevent sunburn by maintaining vigorous canopies through best management practices http://fruitandnuteducation.ucdavis.edu/generaltopics/ .  Proper irrigation, fertilization, pruning, and pest control. Look for symptoms annually right after harvest while there are still healthy leaves on trees. Remove diseased limbs, cutting back to a lateral branch into healthy wood that shows no discoloration. Burn all infested wood, do not chip and use infected wood as mulch.

Additional Resources can be found at:

http://eskalenlab.ucr.edu/handouts/desertdieback.pdf