Crabapple yellow leaves
This tree is probably 40+yrs.....now dropping leaves at random which are yellow. They do not appear spotted, just yellow. Can this be a combination of excess heat and too much water? Soil is clay and tree is surrounded with irrigated grass which has been getting heavy watering during this very warm spring and summer.
Denver County Colorado crab apple trees
It's possible the tree pushed a lot of growth in the spring when we had abundant moisture and cool temperatures. Then when temperatures soared a few weeks ago the tree started shedding some of that lush canopy because the roots couldn't support it. We've seen this on other trees this month in Denver, especially Hackberry.
However, overwatering also causes leaves to turn yellow and drop, and if the overwatering continues, the tree can drown, so adjust your irrigation to water no more than every third day and back off if the heavy rains continue.