The Hormone traps work great, if you set them on the outer edges of the property. The japanese beetle comes in from neighbouring properties homing in on the scents of plants and flowers. The hormone trap triggers reproductive attraction.
I have used them with great success in protecting commercial nurseries, berry farms and garden centres.
You must empty the traps every day.
Spraying the grapes with Ortho, Bug B Gone, etc,,, may not be advisable, if you plan on eating the grapes.