Question
In the past couple of days my tree's leaves are turning yellow and some are
falling off.  The weather has been hot and humid but the ground is wet. We have
a sprinkler system that goes off everyday.  It is in direct sunlight. What could be
the problem?

Answer
Check the fallen leaves and those that are yellow for small holes in the leaf surface that go all the way through.  This would be a condition called shot-hole caused by a fungus.  This is usually not too severe and will cause maybe up to 20% defoliation.  Although not desirable, this will not kill the tree.  The problem could be caused by the change in the environmental conditions as well.  Going from cool, moist to hot and humid conditions can cause this to happen as a normal response of the plant to compensate for the changed environment.  Cut the sprinkler system off so that it only gets watered once per week and then quite well.  Then do not water any more for a week.  You may be stressing the plant in the hot weather with the cool sprinkler water.  I hope changing a couple of these items will stop the problem.  Good Luck.