As fruit gets heavier and heavier on a tree, does the tree use more water?  Or is it sensitive to more water stress?  It's not clear if there is a difference.  We've all seen a lemon tree sigh in relief after the crops been pulled off.  And avocado trees last summer that got hit by the Santa Ana seemed to be more affected the more fruit they had.  In fact, about two weeks after the wind blew, many trees with a heavy fruit load showed clear signs of salt burn or leaf blight.

Now according to work done on olive, the trees actually need more water to avoid stress.  In an Israeli study they measured water use by olive trees with and without fruit and found that there was significant more water use when fruit was present.

http://treephys.oxfordjournals.org/content/early/2016/01/22/treephys.tpv138.full

This is a lot more than we usually allow for in our irrigation scheduling.  Often we don't adjust at all for fruit load.  As fruit sizes most growers do recognize this as a period when stress might cause fruit drop and pay more attention to the trees, but may not alter the irrigation cycle. 

Fruit have stomata just like leaves do, so they do lose water.  Losing too much water leads to flaccid fruit and in the case of avocado easy fruit dehydration and drop.  So we know it's a sensitive period, but maybe we need to be irrigating more frequently.  That's where soil moisture measuring devices help adjust the schedule.  If they are using more water, then irrigate more frequently.

We'll be doing some work over the next few years to verify this.  Stay tuned.