"Watering the grass and plants in the hot summer afternoons will kill the plants!"  Many homeowners live by this statement and arrange their whole schedule as not to be watering when the sun is out.  However, death of the plant can be a slight overstatement.  If that is the case, how do quick rainfalls not kill plant life?  However, watering the turf in the hot weather can cause an outbreak of fungus from the humidity.  Water droplets sitting on the leaf surfaces when watering plants and trees can cause sun burn spots.  If you must water the trees/plants in the warm temperatures, water at the base of the plant, avoiding the leaves.