Growers are still calling in about avocados with thinning canopies, fruit drop and sunburn and leaf death. Coastal avocados are always difficult to irrigate.  Mild weather followed by dry windy conditions means growers have to scramble to get water on.  If the trees are on some sort of calendar schedule, it usually means the trees get stressed.  If trees are on a slope where pressure is not properly regulated, some of the trees are going to get stressed.  If emitter clogging is not addressed, then more trees get stressed.  And lack of rains to leach salts from the root zone, and more trees are stressed. 

This stress sets up the trees for disease and a very common one in an avocado orchard that is filled with lots of leaves where decay fungi are working is stem and leaf blight.  The disease causes defoliation and exposed fruit sun burn and drop.  In an orchard, it's possible to see healthy trees and sick ones at the same time.  This may be due to the differences in soil type from tree to tree or the fruit load on trees - more fruit, more stress.  Looking out over the orchard there may be a polka dot of sick trees.  And it might all happen at once in a week or gradually.

So, this is a problem that is out there, if the irrigation issue is corrected, the trees usually recover.  It might require white washing and pruning out dead tissue.  If it is a young tree under two years, it might actually kill the little tree, but the disease is not usually fatal, just loosing the fruit.

This is a disease that goes to many different tree species - redwoods, eucalyptus, pine, Brazilian pepper, CITRUS.  The cause is the same, water or salinity stress.  To read more about this disease, go to:

http://www.ipm.ucdavis.edu/PMG/r8101311.html

A common sight in an orchard with stem and leaf blight.  Healthy tree in foreground and thinning canopy in back.  Another photo showing the blighted stems on a canopy with surrounding healthier trees.  The die back characteristic on the leaves and random dieback in the leaf.

A common sight in an orchard with stem and leaf blight.  Healthy tree in foreground and thinning canopy in back.  Another photo showing the blighted stems on a canopy with surrounding healthier trees.  The die back characteristic on the leaves.