Try:
CultureInfo en = new CultureInfo("en-US");
Thread.CurrentThread.CurrentCulture = en;
string format = "dd/MM/yyyy";
string Podate = txtPODate.Text.Trim().ToString();
DateTime DT = DateTime.ParseExact(dt1, format, en.DateTimeFormat);
cmd.Parameters.Add("@PODate", SqlDbType.DateTime);
cmd.Parameters[0].Value = DT;
Or add the parameter like this:
cmd.Parameters.Add(new SqlParameter
{
Value = DT,
SqlDbType = SqlDbType.DateTime,
ParameterName = "@PODate"
});