Error while importing data type string to datetime in C#

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C#

I wrote a code to import excel data to SQL. There first I m importing excel data into a data table and that data table i am saving into SQL database.I am having one field data type data time. while importing I am taking all values as a string.I am Saving them with the help of one stored procedure. Saving time I am facing error at date time field.


here is the code.

foreach (DataRow xrow in dt.Rows)
               {


                   string siteid = xrow["siteid"].ToString().Trim();
                   string site = xrow["site"].ToString().Trim();



                   DateTime asd = DateTime.Now;

                   asd = Convert.ToDateTime(xrow["asdate"]);//here I got Error



                   string address = xrow["address"].ToString().Trim();
                   string city = xrow["city"].ToString().Trim();
                   string district = xrow["district"].ToString().Trim();
                   string zone = xrow["zone"].ToString().Trim();
                   string rpname = xrow["rpname"].ToString().Trim();
                   string phno = xrow["phno"].ToString().Trim();
                   string lessor = xrow["lessor"].ToString().Trim();
                   string phone = xrow["phone"].ToString().Trim();

                   string fse = xrow["fse"].ToString().Trim();
                   string contact = xrow["contact"].ToString().Trim();
                   string remark1 = xrow["remark1"].ToString().Trim();
                   string remark2 = xrow["remark2"].ToString().Trim();
                   string prodate = xrow["prodate"].ToString().Trim();
                   string restatus = xrow["restatus"].ToString().Trim();
                   string doctype = xrow["doctype"].ToString().Trim();


                   SqlCommand addrow = new SqlCommand("ProductBulkInsertion", con);
                   addrow.CommandType = CommandType.StoredProcedure;
                   //addrow.Parameters.AddWithValue("@company", company);
                   addrow.Parameters.AddWithValue("@siteid", siteid);
                   addrow.Parameters.AddWithValue("@site", site);
                   addrow.Parameters.AddWithValue("@asdate", asd);
                   addrow.Parameters.AddWithValue("@address", address);
                   addrow.Parameters.AddWithValue("@city", city);
                   addrow.Parameters.AddWithValue("@district", district);
                   addrow.Parameters.AddWithValue("@zone", zone);
                   addrow.Parameters.AddWithValue("@rpname", rpname);
                   addrow.Parameters.AddWithValue("@phno", phno);
                   addrow.Parameters.AddWithValue("@lessor", lessor);
                   addrow.Parameters.AddWithValue("@phone", phone);
                   addrow.Parameters.AddWithValue("@fse", fse);
                   addrow.Parameters.AddWithValue("@remark1", remark1);
                   addrow.Parameters.AddWithValue("@remark2", remark2);
                   addrow.Parameters.AddWithValue("@prodate", prodate);
                   addrow.Parameters.AddWithValue("@restatus", restatus);
                   addrow.Parameters.AddWithValue("@doctype", doctype);
                   addrow.ExecuteNonQuery();

error is

string was not recognized as a valid datetime

What I have tried:

I tried tryparse, tryparse extract and all but failed.I searched net but no suitable answer. So I posted Here.