jQuery Grid Plugin - jqGrid

I use form edit. I want to disable a field ('Date of Lab Confirmed Diagnosis') based on the value of another field ('Report Type'). The field 'Report Type' data type is select. I use dataevents "change". But I don't know the syntax of disabling a field.

Please see my codes below. Any help is highly appreciated!

-Maggie

jQuery(document).ready(function(){
      jQuery("#communicableDiseaseGrid").jqGrid({
           url:'servlet/communicableDiseaseByDateGrid',
           datatype: 'xml',
           colNames:[

                'Report Type',
                'Date Time of Report to HD',
                'Date of Lab Confirmed Diagnosis'
                ],
           colModel :[
              {name:'reportType',
               index:'reportType', 
               editable:true,
               edittype:'select',
               editoptions:{
               value:{'Active_Report':'Active_Report', 'Information_Request':'Information_Request'},
              dataEvents :[
              { type: 'change',
              fn: function(e) {
                                   var thisval = $(e.target).val();
                                   if (thisval=="Active_Report") {
                                          alert ("it is Information_Request, diable Date of Lab Confirmed Diagnosis ");
                                           //how to disable the field  'Date of Lab Confirmed Diagnosis'?
                                                    //?????
                           
                                   }
           }//end func
           } // end type
          ]  // dataevents
               }
          },
          {name:'dateTimeHD', 
            index:'dateTimeHD',  
            sortable:true, 
            sorttype: "date",
            editable:true,
            editrules:{required:true}
          },
             
           {name:'dateLab',
               index:'dateLab', 
               sortable:false,
               editable:true}],
          

          viewrecords: true, 
          caption: 'Communicable Disease'
            }).setGridHeight(150); 

$("#communicableDiseaseButtonEdit").click(function(){
       var gr = jQuery("#communicableDiseaseGrid").jqGrid('getGridParam','selrow');
       if( gr != null ) {
        jQuery("#communicableDiseaseGrid").editGridRow(
         gr,
         {   top: 0,
             left: 0,
             width: 500,
             height:280,
             modal:true,
            drag: true,
            editCaption:  'Edit Record',
            bSubmit: "Submit",
            bCancel: "Cancel",
            url:'servlet/communicableDiseaseByDateGrid?userAction=update',
           processData: "Processing...",
           closeAfterEdit:true,
          reloadAfterSubmit:true,
         }
       
        });
       }
       else alert("Please Select Row");
     });