Remove Datepicker Function dynamically

I want to remove datepicker function depending on the dropdownlist selected value. I try the following codes, but it still shows the calendar when I put the cursor in the text box. Please give me a suggestion.

$("#ddlSearchType").change(function () {
    if ($(this).val() == "Required Date" || $(this).val() == "Submitted Date") {
        $("#txtSearch").datepicker();
    } else {
        $("#txtSearch").datepicker("option", "disabled", true);
    }
});