Use T-Code PPIC.
enter you OM infotype
Click on Extend icon
now select Include screen" and give your correct screen number.
in the next screen select layout editor . here you can hide the field.
Note: this is and ABAP task.Pls ask your ABAP consultat to do this and test it properly wether your requirement is fulfiled. if yes trasport it to PRD.
Regards,
Dinesh
