sort a combined date/ string field

I have a form that I'm viewing service history with a drop down list. All of the information I need is stored in the Service_Request form. I would like to pull out the service date, the type of service and a description of the request.
Below is the code to pull the data from the form assemble it, sort it and place it in the drop down list.

for each rec in Service_Request [Site_ID == ThisAccount.ID]
{
    ThisRequest = rec.Schedule_Date + " - " + rec.Request_Type + " - " + rec.Description_of_Issue;
    ServiceList.add(ThisRequest);
    ServiceList.sort(false);
    Service_History:ui.add(ThisRequest);
}

I would like to sort the list by newest to oldest service dates.

Can anyone point me in a direction to accomplish this?

Alan