Calling all AVOCADO EXPERTS - Is this sun burn on avocado?

[xshen]

My coworker have a huge avocado tree , possibly a seedling of a fuerte, that produces large and delicious avocados prolifically.  However, a lot of the fruit have this black patch on one side of the fruit and it is inedible.  Could this possibly be sunburn?

[xshen]

No one knows why?

[barath]

It could be sunburn or fungal.

Here's a good description of Avocado problems:

http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/DAMAGE/avofruitdam.html

Another great reference is Integrated Pest Management for Avocados (though I don't take their non-organic recommendations):

http://www.ipm.ucdavis.edu/IPMPROJECT/ADS/manual_avocados.html

Update: thought I should mention that if it is Phytophthora Fruit Rot then here's a good page on what to do:

http://www.ipm.ucdavis.edu/PMG/r8100811.html

[xshen]

Thank you Barath for your input.  I found the same info in one of your link that this could be Phytophthora fruit rot but the site mentioned that the rot usually develops after harvest.  All the fruit affected by this disease are rotting while still hanging high on the tree so I was a bit confused.

[barath]

Agreed, that is a bit odd -- how does your coworker water the tree, and is the tree well mulched?

[xshen]

The tree is probably around 20-25 years old with a trunk around 15-18 inches.  It doesn't get regular watering and it's only watered when the lawn irrigation is on.  The tree is not muched and the backyard is covered in st agustine grass.

[barath]

Maybe this isn't something he can do, but my suggestion would be to cover the grass around the tree with newspaper and then mulch on top of the newspaper (so that the tree has at least a 3 ft x 3 ft area with just mulch and no weeds/grass under it), add a few pounds of granulated gypsum, and then give the tree deep watering once every two weeks.  I don't know if this will resolve the issue you're seeing, but it's worth a shot.

[gnappi]

My coworker have a huge avocado tree , possibly a seedling of a fuerte, that produces large and delicious avocados prolifically.  However, a lot of the fruit have this black patch on one side of the fruit and it is inedible.  Could this possibly be sunburn?

Mine will get the sunburn spot if I prune around the fruit and leave it no shade. I never got it if the fruit had leaves around it. If those you show are shaded by leaves it's probably not sunburn.