Question
My Chinese Pistachio Tree was planted about 13 years ago and is now approximately 18 feet tall. The last couple of years I have had a lot of limbs dying. I do not see any insect or scale on the tree. I do not do any deep root fertilizing. I do have a irrigated lawn but do not over water. What can I do to stop the dying?

Roy

Answer
The problem that you describe may be due to environmental stresses or Botryosphaeria canker.  Chinese pistache trees will show dieback during periods of drought and high temperatures.  Given the weather situation in your area this summer, this may partially explain the problem.

Botryosphaeria canker is a disease that causes dieback on limbs and is found basically everywhere.  Botryospheria is a somewhat opportunistic pathogen because it can only enter the tree through wounds.  These wounds may be freeze cracks, hail damage, etc.  Sometimes, they are too small or too high up in the canopy to notice.  The pathogen will enter the wound and start invading the wood.  During stressful periods for the tree, the pathogen will take advantage and invade more quickly.  The result is dieback and dead limbs.

There is no cure for Botryosphaeria canker.  The best recommendation is to remove dead wood by pruning and discard it.  Spores will develop on the bark surface, so it is best not to keep the wood for long periods.  You should maintain proper fertility by fertilizing with a tree and shrub fertilizer during late winter or spring.  It is also helpful to water during periods of drought.  The tree may survive for many years if cared for although it is likely you will continue to have dieback.

If you notice that the leaves are wilting, there may be a different problem.  If you cut into the branches and notice large patches of browning, it may suggest Verticillium wilt.  The internal browning is usually in a ring and is seen in the vascular tissue.  If you search for this disease, you will see images of this discoloration.  There is no cure for this pathogen and usually death happens in 1-2 seasons.  The tree should be removed before it becomes hazardous.

Good luck with your tree.