Ошибка при фильтрации

procedure TForm7.BitBtn1Click(Sender: TObject);
var filtr, add:string;
begin
if Length(Edit1.Text) > 0 then
filtr:='Code_plant LIKE '+#39+Edit1.Text+'%'+#39;
if Length(Edit2.Text) > 0 then
begin
  if Length(filtr) > 0 then add:=' and ' else add:='';
  filtr:=filtr+add+'Name_plant LIKE '+#39+Edit2.Text+'%'+#39;
end;
if Length(Edit3.Text) > 0 then
begin
  if Length(filtr) > 0 then add:=' and ' else add:='';
  filtr:=filtr+add+'Field_name LIKE '+#39+Edit3.Text+'%'+#39;
end;
if Length(DateToStr(DateTimePicker1.Date)) > 0 then
begin
  if Length(filtr) > 0 then add:=' and ' else add:='';
  filtr:=filtr+add+'[Date_planting]>= ' + QuotedStr(DateToStr(DateTimePicker1.Date))+ ' AND [Date_planting]<= '+ QuotedStr(DateToStr(DateTimePicker2.Date));
end;
if Length(Edit5.Text) > 0 then
begin
 if Length(filtr) > 0 then add:=' and ' else add:='';
 filtr:=filtr+add+'Size_plant LIKE '+#39+Edit5.Text+'%'+#39;
end;
if Length(Edit6.Text) > 0 then
begin
 if Length(filtr) > 0 then add:=' and ' else add:='';
 filtr:=filtr+add+'Yield_plant LIKE '+#39+Edit6.Text+'%'+#39;
end;
if (Length(filtr) > 0) then begin
  Form1.DBGrid2.DataSource.DataSet.Filtered:=False;
  Form1.DBGrid2.DataSource.DataSet.Filter:=filtr;
  Form1.DBGrid2.DataSource.DataSet.Filtered:=True;
  Close;
end;
if CheckBox1.Checked=False then filtr:='';
if (Length(filtr) = 0) and (CheckBox1.Checked=True) then
Application.MessageBox('Заполните хотя бы одно поле','Ошибка',MB_OK);
if (Length(filtr) = 0) and (CheckBox1.Checked=False) then
begin
  Form1.DBGrid2.DataSource.DataSet.Filtered:=False;
  Close;
end;
end;